Food Science and Technology
Steve L. Taylor
University of Nebraska
University of Illinois, USA
University College Cork, Republic of Ireland
North Dakota State University, USA
University of Nebraska, USA
Daryl B. Lund
Cornell University, USA
Purdue University, USA
University of Georgia, USA
Ohio State University, USA
A complete list of books in this series appears at the end of this volume.
Ronald S. Jackson
AMSTERDAM BOSTON HEIDELBERG LONDON NEWYORK OXFORD
PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO
About the author
Ronald S. Jackson received his bachelor’s and master’s degrees from Queen’s
University, and doctorate from the University of Toronto. His sabbatical at Cornell
University redirected his academic interest toward viticulture and enology. While
Professor and chair of Botany Department, Brandon University, he developed the
ﬁrst wine technology course in Canada. For many years he was a technical advisor
to the Manitoba Liquor Control Commission, developing sensory evaluation tests
to train and assess members of its Sensory Panel. He was also a long time member
of the MLCC External Tasting Panel. In addition to preparing this book, he is
author of Wine Science: Principles, Practice, Perception, 2e (2000), Conserve Water
Drink Wine (1997) and several technical reviews, including Grape-based Fermenta-
tion Products in Biotechnology: Food Fermentation (1999) and Modern Biotechnol-
ogy of Winemaking in Wine: A Scientiﬁc Evaluation (2002) and articles in the
Encyclopediae of Agricultural Science and Food Sciences and Nutrition. Dr.
Jackson has retired from teaching to devote his time to writing, but is allied with
the Cool Climate Oenology and Viticulture Institute, Brock University. For
questions or suggestions, he may be reached at email@example.com.
The text presents the practice of critical wine tasting, in the context of human sen-
sory perception. Thus, it attempts to differentiate between perception (the human
response to sensation) and sensation itself. Training and experience are usually
required to separate one’s subjective response from objective evaluation.
The techniques described are primarily designed for those involved in wine tast-
ings (judging relative quality or conformity to traditional varietal or regional styles).
These skills are required not only for professional wine evaluation, but also success-
ful winemaking. Although analytic, these procedures can be adapted by the restau-
ranteur or wine merchant, as well as individuals desiring to fully appreciate a wine’s
The reader is ﬁrst guided through the steps of tasting wine. Subsequently, the
psycho-physical and neuroanatomical aspects of sensory response are discussed.
This is followed by a discussion of the optimal conditions for wine assessment and
evaluation, the selection and training of judging ability, preparing various types of
tastings and the analysis of signiﬁcance. Wine classiﬁcation and the origins of wine
quality are covered with a brief discussion of what can conﬁdently be said about
wine and food combination.
References are largely limited to the most recent data whereas Suggested Reading
primarily covers major reference texts.
I should like to express my appreciation to those innumerable researchers who have
dedicated their lives to unraveling the mysteries of human sensory acuity and the
complexities of wine perception.
I must also thank my students, participants of sensory panel tests, and compa-
triots on the External Tasting Panel, and especially Andy Tekauz, for their insights
and views on wine quality.
It is also essential to express my appreciation for the assistance provided by staff
at Academic Press, notably Sara Gorman. Their help and encouragement have
helped bring this book to completion.
Finally, but not least, my thanks must go to my wife who has again suffered from
the author’s widow syndrome.
To the members of the Manitoba Liquor Control Commission.
As beﬁts one of life’s ﬁnest pleasures, wine deserves serious attention. Nevertheless,
no wine tasting procedure has achieved universal acceptance. Most experienced wine
tasters have their own sequence of steps they follow. Although essential for critical
tasting, these steps are too detailed for the dinner table. The difference is equivalent
to the gulf that separates the analysis and enjoyment of music. Critical tasting com-
pares one or several wines against a real or theoretical standard. In contrast, wine
with a meal is intended to be savored as a liquid refreshment. Although critical wine
assessment is ill designed for the dining room, because of distractions of conversa-
tion and the interference of food ﬂavors, the concentration involved in wine analysis
can greatly enhance appreciation.
The technique discussed in Figure 1.1 incorporates suggestions from several
authorities (Broadbent, 1979; Peynaud 1987; Johnson, 1994) and experience gained
from assessing tasters for many years. The synopsis provided is only a starting point.
No technique is ideal for everyone. Probably the most important properties of a seri-
ous taster are the willingness, desire and ability to focus attention on the wine’s
Some authorities advocate rinsing the mouth with wine before embarking on seri-
ous tasting (Peynaud, 1987). This familiarizes the senses with the basic attributes of
the wines to follow. Where tasters are unfamiliar with the characteristics of the
wines, this may be of value. Otherwise, rinsing the mouth with wine seems unneces-
sary. Peynaud also cautions against rinsing the palate between samples. He feels that
water alters sensitivity, and complicates comparing wines. In this recommendation,
Peynaud is at variance with most authorities. Only when the palate seems fatigued
does he support palate cleansing.
Most wines are best sampled in clear, tulip-shaped goblets (Fig. 1.2). The pri-
mary exception involves sparkling wines. These are better judged in elongated,
ﬂute-shaped glasses. They facilitate observation of the wine’s effervescence. All
glasses in a tasting should be identical and ﬁlled to the same level (about one-
quarter to one-third full). This permits each wine to be sampled under equivalent
conditions. Between 30 and 50 ml is adequate for most analyses. Not only are
Each sample should be poured into identical, clear, tulip-shaped, wine glasses. They should each be ﬁlled (1/4 to 1/3 full) with the
same volume of wine.
1 – View each sample at a 30° to 45° angle against a bright, white background.
2 – Record separately the wine’s:
clarity (absence of haze)
color hue (shade or tint) and depth (intensity or amount of pigment)
viscosity (resistance to ﬂow)
effervescence (notably sparkling wines)
II. Odor “in-glass”
1 – Sniff each sample at the mouth of the glass before swirling.
2 – Study and record the nature and intensity of the fragrancea
(see Figs 1.3 and 1.4)
3 – Swirl the glass to promote the release of aromatic constituents from the wine.
4 – Smell the wine, initially at the mouth and then deeper in the bowl.
5 – Study and record the nature at intensity of the fragrance.
6 – Proceed to other samples.
7 – Progress to tasting the wines (III)
III. “In-mouth” sensations
(a) Taste and mouth-feel
1 – Take a small (6 to 10 ml) sample into the mouth.
2 – Move the wine in the mouth to coat all surfaces of the tongue, cheeks and palate.
3 – For the various taste sensations (sweet, acid, bitter) note where they are percieved, when ﬁrst
detected, how long they last, and how they change in perception and intensity.
4 – Concentrate on the tactile (mouth-feel) sensations of astringency, prickling, body, temperature,
5 – Record these perceptions and how they combine with one another.
1 – Note the fragrance of the wine at the warmer temperatures of the mouth.
2 – Aspirate the wine by drawing air through the wine to enhance the release of its aromatic
3 – Concentrate on the nature, development and duration of the fragrance. Note and record any
differences between the “in-mouth” and “in-glass” aspects of the fragrance
1 – Draw air into the lungs that has been aspirated through the wine for 15 to 30 s.
2 – Swallow the wine (or spit it into a cuspidor).
3 – Breath out the warmed vapors through the nose.
4 – Any odor detected in this manner is termed aftersmell; it is usually found only in the ﬁnest or most
Although fragrance is technically divided into the aroma (derived from the grapes) and bouquet (derived
from fermentation, processing and aging), descriptive terms are more informative.
smallvolumes economic, but they facilitate holding the wine at a steep angle (for view-
ing color and clarity) and vigorous swirling (to enhance the release of aromatics).
Except for rare situations, in which color must not inﬂuence assessment, the visual
characteristics of a wine are the ﬁrst to be judged. To improve light transmission, the
glass is tilted against a bright, white background (35° to 45° angle). This produces a
curved edge of varying depths through which the wine’s appearance can be viewed.
Visual stimuli often give a sense of pleasure and anticipation of the sensations to
follow. The appearance may hint at ﬂavor attributes as well as potential faults. The
effect of color on perceived quality is illustrated in Fig. 2.5. It is well known that a
deep red color increases perceived quality, even by seasoned judges. Therefore, visu-
al clues must be used with caution to avoid unfair prejudgement of the wine.
All wine should be brilliantly clear. Haziness in barrel samples is of little concern
because it is eliminated before bottling. Cloudiness in bottled wine is considered
unacceptable, although it seldom affects the wine’s taste or aromatic character.
Because most sources of cloudiness are understood and controllable, haziness in
commercially bottled wine is uncommon. The major exception may involve some
well-aged red wines. Careful pouring or prior decanting can separate the wine from
sediment that may have formed in the bottle.
The two most signiﬁcant features of a wine’s color are its hue and depth.
Hue denotes its shade or tint, whereas depth refers to the relative brightness of the
color. Both aspects can provide clues to features such as grape maturity, duration of
skin contact, fermentation cooperage, and wine age. Immature white grapes yield
almost colorless wines, whereas fully to over-mature grapes generate yellowish wines.
Increased grape maturity often enhances the potential color intensity of red
wine. The extent to which these tendencies are realized depends on the duration of
Tasting process 3
1 – Concentrate on the olfactory and gustatory sensations that linger in the mouth.
2 – Compare these sensations with those previously detected.
3 – Note their character and duration.
V. Repetition of assessment
1 – Reevaluate of the aromatic and sapid sensations of the wines, beginning at II.3—ideally several
times over a period of 30 min.
2 – Study the duration and development (change in intensity and quality) of each sample.
Finally, make an overall assessment of the pleasurableness, complexity, subtlety, elegance, power, balance,
and memorableness of the wine. With experience, you can begin to make evaluations of its potential— the
likelihood of the wine improving in its character with additional aging.
maceration (skin contact). Maturation in oak cooperage speeds age-related color
changes, but it temporarily enhances color depth. During aging, golden tints in white
wines increase, whereas red wines lose color density. Eventually, all wines take on
tawny brown shades.
Because many factors affect wine color, it is impossible to be dogmatic about the
signiﬁcance of a particular color. If origin, style, and age are known, color can indi-
cate the “correctness”of the wine. An atypical color can be a sign of several faults. The
less known about a wine, the less signiﬁcant color becomes in assessing quality. If
color is too likely to be prejudicial, visual clues can be hidden by using black glasses.
Tilting the glass has the advantage of creating a gradation of wine depths. Viewed
against a bright background, a range of color characteristics are observed. The rim
of wine provides one of the better measures of relative wine age. A purplish to
mauve edge is an indicator of youth in a red wine, a brickish tint along the rim is
Overall height: 155 Ϯ 5 mm
Total capacity: 215 Ϯ 10 ml
Figure 1.2 International Standards Organization wine tasting glass. Dimensions are in mm (courtesy
of International Standards Organization, Geneva, Switzerland).
often the ﬁrst sign of aging. In contrast, observing wine down from the top is the
best means of judging relative color depth.
The most difﬁcult task associated with color assessment is expressing one’s impres-
sions meaningfully. There is no accepted terminology for wine colors. Color terms
are seldom used consistently or recorded in an effective manner. Some tasters place
a drop of the wine on the tasting sheet. Although of temporary comparative value,
it does not preserve an accurate record of the wine’s color.
Until a practical standard is available, use of a few, simple, relatively self-
explanatory terms is preferred. Terms such as purple, ruby, red, brick and tawny, and
straw, yellow, gold and amber, combined with qualiﬁers such as pale, light, medium
and dark can express the standard range of red and white wine colors, respectively.
Viscosity refers to the resistance of wine to ﬂow. Factors such as the sugar, glycerol
and alcohol contents affect wine viscosity. Typically, detectable differences in viscos-
ity can be found only in dessert or highly alcoholic wines. Because these differences
are minor and of diverse origin, they are of little diagnostic value. Viscosity is
ignored by most professional tasters.
Spritz refers to the bubbles that may form, usually along the bottom and sides of a
wine glass, or the slight effervescence seen or detected in the mouth. Active and con-
tinuous bubble formation is generally found only in sparkling wines. In the latter
case, the size, number, and duration of the bubbles are important quality features.
Slight bubbling is typically a consequence of early bottling, before the excess dis-
solved carbon dioxide in newly fermented wine has escaped. Infrequently, a slight
spritz may result from malolactic fermentation occurring after bottling. Historically,
spritz was commonly associated with microbial spoilage. Because this is now rare, a
slight spritz is generally of insigniﬁcance.
Tears (rivulets, legs) develop and ﬂow down the sides of glass following swirling.
They are little more than a crude indicator of the wine’s alcohol content. Other than
for the intrigue or visual amusement they may cause, tears are sensory trivia.
Odor – in-glass
Tasters are often counseled to smell the wine before swirling. This exposes the senses
to the wine’s most volatile aromatics. When comparing several wines, it is easier to
position oneself over the glasses than to raise each glass to one’s nose. It makes the
taster aware of one of the wine’s most ethereal attributes.
The second and more important phase of olfactory assessment follows swirling of
the wine. Although simple, effective swirling usually requires some practice. Until
comfortable with the process, start by slowly rotating the base of the glass on a level
surface. Most of the action involves a cyclical arm movement at the shoulder, while
Tasting process 5
the wrist remains stationary. Holding the glass by the stem provides a good grip and
this permits vigorous swirling. As they become familiar with the motion, people usu-
ally shift to swirling by wrist action. Some connoisseurs hold the glass by the edge of
the base. While effective, its awkwardness seems an affectation.
Swirling increases contact between air and the wine, promoting the release of aro-
matic compounds. The in-curved sides of tulip-shaped glasses not only permit vig-
orous rotation, but they also concentrate the released aromatics. Whiffs are taken at
the rim of the glass and then in the bowl. This permits sensation of the fragrance at
different concentrations, potentially generating distinct perceptions. Considerable
attention is usually required in detecting and recognizing varietal, stylistic, or
regional attributes. Repeated attempts may also be required. As the primary source
of a wine’s unique character, the study of fragrance warrants this attention.
Occasionally, glass or plastic covers1
are placed over the mouth of the glass. These
covers serve two purposes. With highly fragrant wines, they limit aromatic contami-
nation of the immediate surroundings. Such contamination can seriously complicate
the assessment of less aromatic wines. The primary function, though, is to permit
especially vigorous swirling of the wine (if held on tightly with the index ﬁnger). This
can be valuable when the wines are aromatically mild.
No special method of inhalation seems necessary when assessing wine (Laing,
1986). Inhalation for more than half a second rarely improves odor identiﬁcation, at
least of single compounds (Laing, 1982). For wines, breathing in for about 2 s seems
fully adequate. Longer periods probably lead to adaptation and loss of sensitivity.
Nonetheless, extended inhalation can be informative with some aromatically com-
plex wines, such as ports. As olfactory receptors become adapted to certain wine
constituents, masked aromatic sensations may become apparent. Although the wine
should be smelled several times, each sniff should be separated by about 30 to 60 s.
Olfactory receptors take about this long to reestablish their intrinsic sensitivity. In
addition, measurements of the rate of wine volatilization suggest that the headspace
(volume just above the wine) takes about 15 s for replenishment (Fischer et al.,
1996). In comparative tastings, each wine should be sampled in sequence. This
avoids odor fatigue from sampling the same fragrance over a short period.
Ideally, assessment of olfactory features should be spread over about 30 min. This
period is necessary to evaluate features such as duration and development. Develop-
ment is often likened to watching a ﬂower open. Development, and the ﬁnish, (see
below) are highly regarded attributes, and particularly important to premium wines.
The higher costs of these wines are justiﬁable only if accompanied with exceptional
Regardless of the technique employed, recording one’s impressions clearly and
precisely is important. This is difﬁcult for everyone, possibly because we are not sys-
tematically trained from an early age to develop verbal-olfactory associations. The
common difﬁculty in recalling odor names has been aptly dubbed “the-tip-of-the-
nose” phenomenon (Lawless and Engen, 1977).
In technical assessments, tasters are usually trained using samples speciﬁcally
For example, watch glasses, 60 mm Petri dish bottoms, or plastic coffee-cup lids.
designed for the purpose. Reference samples for the various terms used are com-
monly available during tastings (Appendices 5.4 and 5.5). Fragrance and off-odor
charts (Figs 1.3 and 1.4) can assist in developing a common and consistent wine
terminology. In a few instances, these terms help deﬁne the aromatic attributes of
varietal wines. However, inappropriate use of odor analogies can mask inability to
accurately describe a wine’s aromatic features.
Emphasis on descriptive terms can be misinterpreted, especially in wine apprecia-
tion courses. Charts should be used only to encourage focusing on the wine’s fra-
grance. Once students recognize the importance of studying the wine’s olfactory
traits, description in terms of speciﬁc fruits, ﬂowers, vegetables, etc. can become
Sulfur, Burnt match
Hydrogen sulfide, etc.
Figure 1.4 Wine off-odor chart (column at right notes examples of casual chemicals) (from Jackson,
2000, reproduced by permission).
counterproductive. For example, fanciful terms are often invented in a vain attempt
to be informative. This tendency is enhanced by the legitimate difﬁculty people have
in adequately describing olfactory sensations. It is generally more advantageous for
consumers to concentrate on recognizing the differences that exemplify varietal char-
acteristics, production styles, and wine age than verbal description. Except for edu-
cational purposes, lexicons of descriptive terms are best left for the purposes for
which they were primarily developed—descriptive sensory analysis.
Impressions (both positive and negative) should be recorded. For this, selection of
an appropriate tasting sheet is important. Figure 1.5 provides an example of a
general wine tasting sheet for wine appreciation courses. Designed for enlargement
to 11 ϫ 17 inch paper, the circles indicate the placement of six glasses of wine.
Reduced photocopies of the labels can be placed in the blank spaces above the six
comment columns. Alternatively, a simple hedonic tasting sheet, such as illustrated
in Figure 1.6, may be adequate. Tasting sheets are discussed in Chapter 5. In addi-
tion to verbal descriptions, a line drawn on a hypothetical scale can visually illustrate
shifts in ﬂavor intensity throughout the tasting (Fig. 1.7). Qualitative changes in fra-
grance can easily be noted on the graph as they occur. The process can rapidly,
clearly, and succinctly express impressions.
Taste and mouth-feel
After an initial assessment of fragrance, attention turns to taste and mouth-feel.
About 6 to 10 ml is sipped. As far as feasible, the volume of each sample should be
kept equivalent to permit valid comparison among samples. Active churning (“chew-
ing”) brings wine in contact with all regions in the mouth.
The ﬁrst taste sensations potentially recognized are those of sweetness and
sourness. Sweetness (if detectable) is generally most noticeable at the tip of the
tongue. In contrast, sourness is more evident along the sides of the tongue and
inside of the cheeks. The sharp aspect of acidity typically lingers considerably
longer than perceptions of sweetness. Because bitterness is detected later, its
increasing perception may coincide with a decline in the detection of sweetness. It
can take upward of 15 s before bitterness reaches its peak, usually in the central,
posterior portion of the tongue. Therefore, it is advisable to retain the wine in the
mouth for at least 15 s. Subsequently, the taster should concentrate on mouth-feel
sensations, such as the dry, dust-in-the-mouth aspect of astringency, and the per-
ceptions of burning (alcohol or phenol-induced sensations), or the prickling aspect
of carbon dioxide (if present at concentrations above 0.3 g/100 ml). These and
other tactile sensations are dispersed throughout the mouth, without speciﬁc
As indicated, differences in the sequence of detection can conﬁrm speciﬁc taste
sensations (Kuznicki and Turner, 1986). However, the duration of these sensations is
not particularly diagnostic. Persistence reﬂects more the concentration and maxi-
mum perceived intensity of the tastant than its category (Robichaud and Noble,
1990). Although signiﬁcant in some critical tastings, the purpose of noting sapid
Tasting process 9
Color – hue
Score (Maximum ؉/؊1)
Berry Fruit – Blackberry, Blackcurrant, Grape,
Melon, Raspberry, Strawberry
Tree Fruit – Apple, Apricot, Banana, Cherry,
Lemon. Litchi, Peach, Passion Fruit,
Dry Fruit – Fig,Raisin
Floral – Camellia, Citronella, Iris,
Orange blossom, Rose, Tulip, Violet
Nuts – Almond,Hazelnut,Walnut
Vegetable – Asparagus, Beet, Bell pepper,
Canned Green beans, Hay, Olives,
Spice – Cinnamon, Cloves, Incense, Licorice,
Roasted – Caramel, Coffee, Smoke, Toast
Other – Buttery, Cheese, Cigar box, Honey,
Leather, Mushroom, Oak, Pine,
Phenolic, Truffle, Vanilla
Score (Maximum 5)
Sweetness, acidity, astringency, bitterness,
body, heat (alcohol level), mellowness,
Score (Maximum 3)
Score (Maximum 1)
TOTAL SCORE (Maximum 10)
sensations is not as important as focusing on how they interact to generate the over-
all perceptions of balance, ﬂavor, and body.
There are differing opinions on whether taste and mouth-feel should be
assessed with the ﬁrst sip or during subsequent samplings. Tannins react with
proteins in the mouth, diminishing their potential bitter and astringent sensa-
tions. Reaction with saliva proteins partially explains why the ﬁrst sample is usu-
ally less bitter and astringent than subsequent samples. The ﬁrst taste more
closely simulates the perception generated when wine is taken with a meal. If this
is an important aspect of the tasting, it is essential that the tasting progress
slowly. This permits stimulated salivary production to compensate for its dilution
Odor – retronasal
To enhance the in-mouth detection of fragrance, tasters frequently aspirate the
wine. This involves tightening the jaws, contracting the cheek muscles (to pull the
Tasting process 11
Intensity: the perceived relative strength of the sensation—too weak or too strong are equally undesirable.*
Duration: the interval over which the wine develops or maintains its sensory impact; long duration is
usually a positive feature if not too intense.
Quality: the degree to which the feature reflects appropriate and desirable varietal, regional or stylistic
features of the wine, plus the pleasure these features give the taster.
Figure 1.6 Hedonic
wine tasting sheet for
quality assessment (from
lips slightly ajar), and slowly drawing air through the wine. Alternatively, some
tasters purse the lips before drawing air through the wine. Either procedure
increases volatilization—analogous to swirling wine in a glass. Although less effec-
tive, vigorous agitation of the wine in the mouth has a similar effect. The liber-
ated aromatic compounds ﬂow up into the nasal passages, producing what is
called retronasal olfaction. The combination of retronasal olfaction with taste and
mouth-feel generates the sensation of ﬂavor. The perceptions observed should be
recorded quickly, as they can change unpredictably. The signiﬁcance of retronasal
olfaction to ﬂavor detection is easily demonstrated by clamping the nose. This
limits the movement of aromatics from the oral cavity up into the nasal passages.
Some tasters complete their assessment of the wine’s fragrance with a prolonged
aspiration. Following inhalation, the wine is swallowed, and the vapors slowly
exhaled through the nose. Any aromatic sensations detected are called the after-
smell. While occasionally informative, it is typically of value only with highly aro-
matic wines, such as ports.
Following assessment, the wine is either swallowed or expectorated. In wine
appreciation courses, wine societies, and the like, the samples are typically con-
sumed. Because the number of wines being tasted is often small, and assessment
not critical, consumption is unlikely to seriously affect tasting skill. However,
twenty or more wines may be sampled in wine competitions or technical tastings.
Consequently, consumption is assiduously avoided. Scholten (1987) has shown
that expectoration avoids signiﬁcant amounts of alcohol accumulating in the
blood. Nevertheless, sufﬁcient tannic material may be consumed to induce a
One of the occupational hazards of wine tasting can be headaches. This appears
to be especially so in individuals producing low levels of platelet-bound phenolsul-
after 20 min
Figure 1.7 Graphic representation of the development of a wine’s fragrance during a tasting. Speciﬁc
observations can be applied directly to the point on the graph where the perception was detected.
fotransferase (PST) (Alam et al., 1997). PST inactivates the action of biogenic
amines and catacholamines that dilate small blood vessels in the brain, possibly
through the release of prostaglandins. In some people (including the author),
headache development is often prevented by the prior consumption of prostaglandin
synthesis inhibitors, such as acetylsalicylic acid (e.g., aspirin), acetaminophen (e.g.,
), and ibuprofen (e.g., Advil®
) (Kaufman, 1992). Large polymeric tannins,
such as those that form during aging, are unable to enter the bloodstream through
the intestinal wall. This probably explains why aged red wines induce fewer
headaches and suppress the action of PST than their younger counterparts.
Finish refers to the aromatic and sapid sensations that linger following swallowing or
expectoration. It is the vinous equivalent of a sunset—typically, the longer the ﬁn-
ish, the more highly rated the wine. Some tasters consider its duration a major indi-
cator of quality. Fruity–ﬂoral essences, associated with refreshing acidity, epitomize
most superior white wines; while complex berry fragrances combined with ﬂavorful
tannins exemplify the best red wines. Fortiﬁed wines, possessing more intense ﬂavors,
have a very long ﬁnish. Exceptions to the generally desirable nature of a protracted
ﬁnish are features such as a persistent metallic aspect, or excessively acidic, bitter and
After the sensory aspects have been studied individually, attention shifts to integrat-
ing the various sensations. This may involve aspects of conformity with, and
distinctiveness within, regional standards;2
the development, duration, and com-
plexity of the fragrance; the duration and character of the ﬁnish; and the uniqueness
of the tasting experience.
Many of the terms used for overall quality have been borrowed from the world
of art. Relative to wine, the term complexity refers to the presence of many, dis-
tinctive, aromatic elements, rather than one or a few easily recognizable odors.
Balance (harmony) denotes the perceptive equilibrium of all olfactory and sapid
sensations, where individual perceptions do not dominate. The complex interac-
tion of sensory perceptions in the origin of balance is evident in the reduced
fruitiness of red wines possessing excessive astringency, or the imbalance of a
sweet wine lacking sufﬁcient fragrance. Balance may appear to be simpler to
achieve in white wines because of their low phenolic content. White wines are also
typically less aromatically complex. Nonetheless, balance in white wines is no eas-
ier to achieve than in red wines. Occasionally, individual aspects may be sufﬁ-
ciently intense to give the impression that balance is on the brink of collapse. In
Tasting process 13
Like grammar, traditional quality standards are the result of historical precedent. The attributes con-
sidered appropriate for a particular wine have evolved through the cyclical interaction of winemakers and
this situation, the balance has an element of nervousness that can be particularly
fascinating. Development designates changes in the aromatic character that occur
throughout the sampling period. Ideally, these changes maintain interest and keep
drawing one’s attention back to its latest transformation. Duration refers to how
long the fragrance retains a unique character, before losing its individuality, and
becoming just vinous. Interest is the combined inﬂuence of the previous factors
on retaining the taster’s attention. Implied, but not often speciﬁcally stated, is the
requirement for both power and elegance in the wine’s sensory characteristics.
Without these attributes, attractiveness is short-lived. If the overall sensation is
sufﬁciently remarkable, the experience becomes unforgettable, an attribute
Amerine and Roessler (1983) call memorableness.
Most European authorities feel that quality should be assessed only within
regional appellations, counseling against comparative tastings among regions or
grape varieties. Although these restrictions make tastings simpler, they negate much
of their value in promoting quality improvement. When tasting concentrates on
artistic quality, rather than stylistic purity, comparative tasting can be especially
revealing. Comparative tastings are more popular in the UK and the New World,
where artistic merit tends to be considered more highly than compliance with
Baldy, M. W. 1995. The University Wine Course. 2nd ed. Wine Appreciation Guild,
San Francisco, CA.
Broadbent, M. (1979) Wine Tasting. Christie’s Wine Publications, London.
Alam, Z., Coombes, N., Waring, R. H., Williams, A. C., and Steventon, G. B. (1997).
Platelet sulphotransferase activity, plasma sulfate levels, and sulphation capac-
ity in patients with migraine and tension headache. Cephalalgia 17, 761–764.
Amerine, M. A., and Roessler, E. B. (1983). “Wines, Their Sensory Evaluation.” 2nd
ed., Freeman, San Francisco, CA.
Broadbent, M. (1979). “Wine Tasting.” Christie’s Wine Publications, London.
Fischer, C., Fischer, U., and Jakob, L. (1996). Impact of matrix variables, ethanol,
sugar, glycerol, pH and temperature on the partition coefﬁcients of aroma com-
pounds in wine and their kinetics of volatization. In: “Proc. 4th Int. Symp. Cool
Climate Vitic. Enol., Rochester, NY, July 16–20, 1996.” (T. Henick-Kling, T. E.
Wolf, and E. M. Harkness, eds.), pp. VII, 42–46. NY State Agricultural Exper-
imental Station, Geneva, New York.
Jackson, R. S. (2000). “Wine Science: Principles, Practice, Perception” 2nd ed. Aca-
demic Press, San Diego, CA.
Johnson, H. (1994). “The World Atlas of Wine.” Simon & Schuster, New York.
Kaufman, H. S. (1992). The red wine headache and prostaglandin synthetase
inhibitors: A blind controlled study. J. Wine Res. 3, 43–46.
Kuznicki, J. T., and Turner, L. S. (1986). Reaction time in the perceptual processing
of taste quality. Chem. Senses 11, 183–201.
Laing, D. G. (1982). Characterization of human behaviour during odour perception.
Perception 11, 221–230.
Laing, D. G. (1986). Optimum perception of odours by humans. In: “Proc. 7 World
Clean Air Congress, Vol. 4, pp. 110–117.” Clear Air Society of Australia and
Lawless, H. T., and Engen, T. (1977). Associations of odors, interference, mnemon-
ics and verbal labeling. J. Expt. Psychol. Human Learn. Mem. 3, 52–59.
Peynaud, E. (Trans. by M. Schuster) (1987). “The Taste of Wine. The Art and
Science of Wine Appreciation.” Macdonald & Co, London.
Robichaud, J. L., and Noble, A. C. (1990). Astringency and bitterness of selected
phenolics in wine. J. Sci. Food Agric. 53, 343–353.
Scholten, P. 1987. How much do judges absorb? Wines Vines 69, (3) 23–24.
As noted in Chapter 1, wine appearance can provide useful indicators of quality,
style, and varietal origin. Unfortunately, it can also provide false clues and prejudice
assessment. In this chapter, the nature, origin, and signiﬁcance of the visual aspects
of wines are discussed.
Color perception and measurement
The visual characteristics of a wine depend on how its chemical and particulate
nature transmit, absorb, and reﬂect visible radiation. For example, the pigments in a
red wine reﬂect (and absorb) speciﬁc wavelengths of visible radiation. These induce
reactions in the retina of the eye that generate the impression of red. The color inten-
sity depends on the amount and chemical state of the pigments present, and corre-
spondingly the quantity and quality of light reﬂected. The purity of the color
depends on the relative absorptive properties of the pigments across the visible spec-
trum. The broader the spectrum, the less pure the perceived color (indicated by a
higher “tint” value; Fig. 2.1).
Although such characteristics can be accurately measured with a spectropho-
tometer (Fig. 2.1), the relevance of the data to human color perception is far from
simple. Spectrophotometric measurements assess the intensity of individual wave-
lengths, whereas human perception combines the responses from many neurons
(cones and rods) in the retina. Each cone responds to a relatively narrow range of
wavelengths, with peak sensitivity in either the blue-violet (437 nm), green (533 nm)
or yellow (564 nm) regions. The green- and yellow-absorbing cone pigments show
considerable overlap. In contrast, the rods react nonspeciﬁcally to low-intensity light.
Color perception results from the combined impulses from the three types of cones,
while brightness and clarity are the prerogative of the rods. In addition, the eye pos-
sesses additional receptor cells (P and M) that help coordinate the stimuli from the
rods and differentiate contrast. Finally, color perception involves a comparison of
the nerve responses at the boundary where color changes. This probably is the origin
of the color constancy that occurs under most daily changes in sunlight spectral
quality (Brou et al., 1986; Fig. 5.1). Thus, color perception of natural objects is a
complex collation of responses, not a simple reaction to individual wavelengths or
their respective intensities.
There is no generally accepted classiﬁcation of wine color. It is also notoriously
difﬁcult to adequately represent the color of wine on photographic paper or ﬁlm.
Although people can differentiate thousands of color gradations by direct compari-
son, they tend to consistently differentiate comparatively few by name (Fig. 2.2).
Many terms are used synonymously (Chapanis, 1965). Therefore, the number of
color terms generally used for wine colors should be limited and kept simple to aid
consistent use. Color terms should incorporate aspects of hue (wavelength purity),
saturation (greyness) and brightness (capacity to reﬂect or transmit light). Their
combination reﬂects the difﬁculty people have in differentiating these aspects of
18 Visual perceptions
1 0 531 8.05 12.20 0.52
2 4 520 11.80 18.60 0.58
3 16 515 7.95 13.45 0.69
4 28 515 5.20 9.40 0.81
Figure 2.1 Absorbance scans of a single cultivar port (Touriga Nacional, 1981) at different ages (from
Bakker and Timberlake, 1986, reproduced by permission).
0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
Coefficient of consistancy, C
Figure 2.2 Coefﬁcients of consistency for the selections made to 233 color names (from Chapanis, 1965).
color. For example, both yellow–red and brown commonly would be described as hues.
Technically, however, yellow–red is a hue (precise region along the visible spectrum),
whereas brown is an impure yellow–red (combining yellow–red and blue spectral
elements). Equally, moderate pink is partially saturated light red. Figure 2.3 illustrates
the three fundamental characteristics of color—hue, saturation and brightness.
A readily available standard of wine colors would increase the value of color in
sensory evaluation. The Munsell color notation (Munsell, 1980) has a long history
of use in the food industry and scientiﬁc investigation. However, its expense and
unfamiliar color designation system (e.g., 5 YR 4/6—a moderate orange–brown)
has precluded its more general adoption. Genetic variability in color perception
also limits the applicability of a standard. Color blindness is the best-known exam-
ple, but more subtle deﬁciencies are widespread. Color perception also changes
with age. Yellow pigment accumulates in the lens and retina, resulting in a slow loss
in blue sensitivity.
While difﬁculties remain in correlating spectral absorbance to perceived color,
simple techniques can yield valuable data. One technique measures the absorbance
of undiluted samples of red wine at 420 nm and 520 nm (Somers and Evans, 1977).
Figure 2.3 Schematic representation of the psychological dimensions of color space (from Chapanis,
The sum of these values is a measure of color depth, while their ratio estimates tint.
Absorbance at 420 nm provides an indicator of a brown cast, while absorbance at
520 nm assesses redness. As red wines age, the level of yellowish polymeric pigments
increases, and the impact of monomeric red anthocyanins decreases. Besides the
resulting shift toward brown, there is also pigment loss and reduction in color depth.
In white wines, absorbance at 420 nm is an indicator of browning (Peng et al., 1999).
Although useful, absorbance at 420 and 520 nm is too crude to adequately reﬂect
small differences in color. Additional data, such as the proportion of colored (ion-
ized) monomeric anthocyanins, total anthocyanin and phenol contents, and the pro-
portion of anthocyanins complexed to various phenolic polymers, may be derived
from acidiﬁcation with hydrochloric acid, decolorization with metabisulﬁte, and sub-
sequent recoloration with acetaldehyde, respectively (Somers and Evans, 1977).
Because the proportion of complexed anthocyanins increases with age, it has been
described as the wine’s “chemical age.” Several studies have shown a strong correla-
tion between the amount of colored (ionized) anthocyanins and the perceived qual-
ity of young red wines (Somers and Evans, 1974; Somers, 1998).
Another means of objectively assessing wine color employs tristimulus colorime-
try. It involves taking three separate intensity measurements of light transmitted
through wine, using red, green and blue ﬁlters. This approximates the response of the
human eye. Appropriate measurements may be obtained with a spectrophotometer,
but these require complicated mathematical transformations. Tristimulus colorime-
ters directly correlate the values with color vision. Estimates of brightness (clarity),
chroma (saturation) and hue angle (shade) are generated. These are the three param-
eters normally used in deﬁning color.
Another means of estimating color response involves the CIE (Commission Inter-
nationale de l’Eclairage) system. The CIE system involves measuring light transmis-
sion at three wavelengths (445, 550, and 625 nm), and occasionally at 495 nm. These
data can be used to derive values for L (relative lightness), a (relative redness) and
b (relative yellowness). These can be used either in the Hunter L*a*b* or CIELAB
measurements. These scales have been used to measure wine color, though several
researchers have proposed changes to make the values more applicable to wine
(Negueruela et al., 1995; Ayala et al., 1997). The information is particularly suited to
determining color differences. This information can improve the blending of wines
to a predetermined color (Negueruela et al., 1990), but it has found little use in wine
Signiﬁcance in tasting
Color often affects quality perception (Williams et al., 1984a; Fig. 2.4; Fig. 2.5 ), as
well as taste perception (Maga, 1974; Clydesdale et al., 1992). For red wines, ﬂavor
intensity (and wine quality) has often been correlated with color density (Iland and
Marquis, 1993) and hue (the proportion of red “ionized” anthocyanins) (Somers
and Evans, 1974; Bucelli and Gigliotti, 1993). Wine ﬂavors, located primarily in the
skins, are likely to be extracted under the same conditions that promote pigment
extraction. Color depth is also considered an indicator of aging potential.
20 Visual perceptions
Occasionally, wines are sampled in black wine glasses, or under red light, to negate
Often tasters associate particular colors with certain wines. Young, dry, white
wines generally range from nearly colorless to pale straw colored. A more obvious
yellow tint may suggest long maceration or maturation in oak cooperage. Sweet
white wines may vary from a pale straw to yellow–gold. Sherries vary from pale
straw to dark golden-brown, depending on the style. Rosé wines are expected to be
pale to light pinkish or rosé, without shades of blue. Hints of brown, purple, or
orange usually indicate oxidation. Red wines vary from deep purple to pale tawny
red. Initially, most red wines have a purplish-red hue, especially noticeable at the
edge of the wine. Red ports, depending on the style, may be deep red, ruby, or tawny
Because wines eventually take on brownish hues, brownness is often used as an
indicator of age. This feature is indicated by a lowering of the A420
tometric ratio (Somers and Evans, 1977). However, a brownish cast may equally indi-
cate oxidation or heating. Therefore, wine age, type, and style must be known before
30 40 50 60 70 80 90
Wine quality (%, light)
Figure 2.4 Illustration of the relationship between wine quality assessed by smell and taste (in
darkness) and by sight alone (from color) compared with quality assessed by all three senses (light)
(from Tromp and van Wyk, 1977, reproduced by permission).
interpreting the meaning and signiﬁcance of a brownish hue. Brown shades are
acceptable only if associated with the development of a desirable processing or aged
bouquet. The heating of madeira, which gives the wine its brown coloration and
baked bouquet, is an example of process-produced browning. Because most wines
fail to develop a desirable aged bouquet, brown casts often mean that the wine is
“over the hill.”
Most of the data suggest that color inﬂuences are learned associations (see
explanations may be possible. Regardless of origin, the effects probably arise from
visual, taste and olfactory messages interacting in the orbitofrontal cortex (Fig. 3.8).
Anthocyanins are the primary determinants of color in red grapes and wine. In
grapes, anthocyanins occur predominantly as glucosides. These are conjugates with
one or more glucose molecules. The complex both increases chemical stability and
water solubility. The glucoside may also associate with acetic, coumaric, or caffeic
22 Visual perceptions
60 64 68 72 76 80 84
30 40 50 60
Flavor acceptance (%)
Color acceptance (%)
70 80 90
Figure 2.5 Relation between ﬂavor and odor acceptance (A) and color and ﬂavor acceptance (B)
(from Pokorny´ et al., 1998, reproduced by permission).
Five classes of anthocyanins occur in grapes—the cyanins, delphinins, malvins,
peonins, and petunins. They are differentiated relative to the number of hydroxyl and
methyl groups on the B ring of the anthocyanidin molecule (Table 2.1). The content
and relative amounts of each class vary considerably among cultivars and with grow-
ing conditions (Wenzel et al., 1987). The hydroxylation pattern of the anthocyanidin
B ring primarily controls both the hue and color stability. Free hydroxyl groups
enhance blueness, whereas methylation augments redness. In addition, the presence
of two hydroxyl groups next to each other on the B ring (o-diphenols) markedly
enhances their potential to oxidize. Therefore, wine with a high proportion of malvin
or peonin, neither of which possess o-diphenols, signiﬁcantly enhances color stabil-
ity. Resistance to oxidation is also a function of conjugation of the anthocyanin with
sugar and other compounds (Robinson et al., 1966). In most red grapes, malvin is
the predominant anthocyanin. Because it is the reddest of anthocyanins, the red hue
of most young red wine comes from this compound.
Besides the ﬁve main types of anthocyanins, each type occurs in a dynamic equi-
librium among ﬁve major molecular states in wine. Four are free forms and one is
bound to sulfur dioxide (Fig. 2.6). Most are colorless within the pH range of wine.
Those that exist in the ﬂavylium state generate a red hue, while those in the quinoidal
state give a bluish tint. The proportion of each state depends primarily on the pH
and free sulfur dioxide content of the wine. Low pH enhances redness (favors the
ﬂavylium state), whereas high pH generates a blue–violet cast (by favoring the
quinoidal state). Color density is also affected. Bleaching of anthocyanins by sulfur
Speciﬁc name R3
Cyanidin OH OH
Delphinidin OH OH OH
= glucose (bound at the glucose
= glucose (bound at the
After Methods for Analysis of Musts and Wines, MA Amerine and CS Ough, Copyright 1980 John Wiley
and Sons, Inc. Reprinted by permission of John Wiley and Sons, Inc.
Table 2.1 Anthocyanins occurring in winea
dioxide (either an additive, or produced by yeasts during fermentation) can further
diminish color depth.
In grapes, anthocyanins exist primarily in stacked conglomerates, induced by
processes called self-association and copigmentation. Hydrophobic interactions
between individual anthocyanidins (self-association) or between anthocyanidins and
other phenolic compounds (co-pigmentation) hold the aggregates together. Both
complexes increase light absorbency and color density. During viniﬁcation and mat-
uration, these conglomerates tend to disassociate. Anthocyanin molecules freed into
the acidic wine environment lose their bluish color. In addition, disassociation also
results in reduced light absorption and loss in color depth. Typical losses in color
density can vary from two- to ﬁve-fold, depending on the pH, ethanol, and tannin
24 Visual perceptions
Bisulfite addition flavene
Quinoidal base (blue–violet)
Flavylium cation (red)
Figure 2.6 Equilibria among the major molecular states of anthocyanins in wine: Gl, glucose (from
Jackson, 2000, reproduced by permission).
contents of the wine. Nevertheless, sufﬁcient self-association complexes seem to sur-
vive to generate the purple tint characteristic of most young red wines. These color
changes occur without a reduction in the absolute anthocyanin content.
During maturation, not only do anthocyanin aggregates disassociate, but individual
anthocyanin molecules tend to lose their sugar and acyl (acetate, caffeate, or
coumarate) constituents. This makes them more susceptible to both irreversible oxida-
tion (browning), and to conversion of the colored ﬂavylium state to colorless hemiac-
etals. To limit these events, it is important that the wine contains signiﬁcant quantities
This explains most the brownish shift that occurs during the aging of red wines.
The concurrent extraction of tannins with anthocyanins during fermentation is
critical to long-term color stability in red wines. These compounds begin to polymer-
ize with free anthocyanins almost immediately. By the end of fermentation, some 25%
of the anthocyanins may exist polymerized with tannins. This can rise to about 40%
within 1 year in oak cooperage (Somers, 1982). Subsequently, polymerization contin-
ues more slowly, and it may approach 100% within several years (Fig. 2.7). Thus, red
color not only reﬂects the amount, nature, and states of the anthocyanin content of a
wine, but also the types and amounts of tannin subunits extracted and retained dur-
ing and after viniﬁcation (McCloskey and Yengoyan, 1981). The poor color stability
of most red muscadine wines appears to involve the absence of appropriate tannins
and acylated anthocyanins in muscadine grapes (Sims and Morris, 1986).
Polymerization protects the anthocyanin molecule from oxidation or other chem-
ical modiﬁcations. Incidently, polymerization also increases solubility, minimizing
tannin and pigment loss by precipitation. In addition, more anthocyanin molecules
are colored in tannin complexes, because of increases in the proportion of both the
ﬂavylium and quinoidal states. For example, about 60% of anthocyanin–tannin poly-
mers are colored at pH 3.4, whereas 20% of equivalent free anthocyanins are colored
2 4 6 8 10
Age of wine (years)
Figure 2.7 Increase in the contribution of polymeric pigments to wine color density during the aging of
Shiraz wines: ᭡, mean values: ᭹, extremes (from Somers, 1982, reproduced by permission).
(Fig. 2.8). The yellow-brown ﬂavylium and quinoidal anthocyanin–tannin polymers
generate the age-related brickish shades.
Polymerization of anthocyanins with procyanidins occurs slowly in the absence of
oxygen. Nevertheless, polymerization is promoted by the oxygen inadvertently
absorbed during racking. The small amounts of peroxide generated, as oxygen reacts
with tannins, oxidizes ethanol to acetaldehyde. The subsequent reaction of acetalde-
hyde with anthocyanins promotes their polymerization with procyanidins (tannin
subunits). The initially small anthocyanin–acetaldehyde–procyanidin polymers are
thought to accentuate the violet shift so typical of young red wines (Dallas et al.,
1996). Acetaldehyde also reacts with sulfur dioxide, removing it from anthocyanins.
This not only reverses the bleaching action of sulfur dioxide, but also liberates the
anthocyanin for polymerization with procyanidins.
Other mechanisms suspected in color stabilization involve various yeast metabo-
lites, notably pyruvic acid. It can react with anthocyanins (Fulcrand et al., 1998),
generating a tawny red color. Monoglucosides and coumaroyl monoglucosides of
generating red–orange pigments (Fulcrand et al., 1997).
As red wine ages, its color reﬂects the increasing proportion of anthocyanin–tannin
polymers. Table 2.2 illustrates the various forms producing yellow, yellow–red,
yellow–brown, red, and violet shades. The reduction in color density that also accom-
panies aging may result from oxidation, structural changes in anthocyanin–tannin
polymers, and polymer precipitation with tartrate salts or soluble proteins.
Red wines can vary from deep red-purple to pale tawny red. The purplish-red hue
of young red wines may be a result of the continuing presence of anthocyanin
26 Visual perceptions
1 3 4 52
Figure 2.8 Equilibria among different forms of A free anthocyanins (A) and B combined anthocyanins
(T-A) extracted from wine. +
, red ﬂavylium cation; OH, colorless carbinol pseudobase; O, blue–violet
quinoidal base (from Ribéreau-Gayon and Glories, 1987, reproduced by permission).
complexes or anthocyanin–acetaldehyde–tannin polymers, but it may also indicate
that the pH of the wine is undesirably high (>3.8). A light color may indicate grape
immaturity or poor winemaking practices. However, certain cultivars, such as Gamay
and Pinot noir, seldom yield wines with deep colors. Spätburgunder wines from Ger-
many are typically so pale colored as to often resemble a dark rosé. Cool climatic con-
ditions are also not conducive to the production of dark-colored red wines. In these
situations, the varietal origin must be known to avoid unduly penalizing the wine.
More intensely pigmented varieties, such as Nebbiolo and Cabernet Sauvignon,
may remain deep red for decades. Dark shades often correlate with rich ﬂavors.
These are probably extracted along with anthocyanins from the skins. Standard vini-
ﬁcation procedures favor the uptake of high levels of tannins. These generate the bit-
ter and astringent sensations that take prolonged aging to soften. However, use of
rotary fermentors favors the early extraction of berry ﬂavors and intense coloration,
before tannin uptake reaches high levels.
Most red wines begin to take on a noticeable brickish red cast within a few years,
especially when long aged in oak cooperage (Fig. 2.1). Brickish red or tawny red col-
ors are acceptable only if linked to the development of a favorable aged bouquet. In
most standard red wines, these hues indicate only that the wine has lost the fruitiness
it might have had. In young red wines, brick shades may suggest overheating (as in a
warehouse where it would be associated with a baked odor), or a faulty closure (and
an associated oxidized odor).
Rosé wines are expected to be pale pink, cherry, or raspberry colored, without shades
of blue. The actual shade depends on the amount and type of anthocyanins found
in the cultivar(s) used. An orangish cast is generally undesirable, but this is charac-
teristic of rosés made predominantly from Grenache. Otherwise, hints of orange
Color Molecular weight (kDa)
AOH Noncolored 500
P Noncolored 600
T Yellow 1000–2000
T-AOH Noncolored 1000–2000
TC Yellow-red 2000–3000
TtC Yellow-brown 3000–5000
TP Yellow 5000
From Ribéreau-Gayon and Glories (1987), reproduced by permission.
A, Anthocyanin; P, procyanidin; T, tannin; TC, condensed tannin; TtC, very condensed tannin; TP,
tannin condensed with polysaccharides; OH, carbinol pseudobase; O, quinoidal base; HSO3
Table 2.2 Color and molecular weight of some wine phenolsa
usually suggest oxidation. Purplish hints often signify that the wine is too high in pH
and may taste ﬂat.
In comparison with red wines, little is known about the chemical nature and develop-
ment of color in white wine. The small phenolic content of white wines consists mostly
of hydroxycinnamates, such as caftaric acid and related derivatives. On crushing,
these readily oxidize and form S-glutathionyl complexes. These generally do not turn
brown. Thus, it is believed that most of the yellowish pigmentation in young white
wine is derived from the extraction and oxidation of ﬂavonols, such as quercetin and
kaempferol. Nonﬂavonoids and lignins extracted from oak cooperage during wine
maturation can add signiﬁcantly to the color of white wines. The deepening yellow–
gold of older white wines probably comes from the oxidation of phenols or galactur-
onic acid. However, gold shades may also develop following the formation of
melanoidin compounds by Maillard reactions, or the caramelization of sugars. Occa-
sionally, a pinkish cast is detectable in wines made from Gewürztraminer. This comes
from trace amounts of anthocyanins extracted from the skins of this pinkish cultivar.
The coloration in some so-called white wines made from red varieties also comes from
the extraction of anthocyanins from skins. In fortiﬁed sweet wines, much of the color
comes from either oxidation of phenolics in the wine, or from melanoid pigments,
formed during heat concentration of grape juice used for sweetening.
Typically, young, dry, white wines range from nearly colorless to pale straw col-
ored. A more obvious yellow tint may be considered suspicious, unless associated
with extended skin contact (maceration), or maturation in oak cooperage. The wine
takes on deeper hues with aging. If associated with the development of an appreci-
ated aged bouquet, it is desirable. If associated with accidental oxidation, and the
presence of an aldehyde odor, it is unacceptable. In contrast, unusually pale colors
may suggest the use of unripe grapes (absence of typical coloration, high acidity,
little varietal character), removal of the juice from the skins without maceration
(extraction of few phenolics and minimal varietal ﬂavor), or the excessive use of sul-
fur dioxide (which has a bleaching action). Sweet white wines generally are more
intensely colored, being straw-yellow to yellow-gold. This probably results from the
in-berry oxidation of grape constituents during over-ripening. Sherries vary from
pale straw to golden-brown, depending on the particular style (ﬁno to oloroso), and
the degree to which they are sweetened. Madeiras are always amber colored (unless
decolorized) because of the heat processing they undergo. Although white wines typ-
ically darken with age, some fortiﬁed white wine may lighten (e.g., Marsala). This
results from the precipitation of melanoid pigments.
In contrast to the complexity of interpreting the signiﬁcance of color, haziness is
always considered a fault. With modern techniques of clariﬁcation, wine consumers
28 Visual perceptions
now expect a clear product with long shelf-life. Consequently, considerable effort is
expended in producing wines stable in terms of clarity.
Young wines remain supersaturated with tartrate salts after fermentation. During
maturation, isomerization of these salts reduces solubility. Consequently, storage
under cool conditions often leads to crystallization. Crusty, ﬂake-like crystals are
usually potassium bitartrate (cream of tartar), whereas ﬁne crystals are typically cal-
As the alcohol content rises during fermentation, the solubility of bitartrate
decreases. This induces the slow precipitation of potassium bitartrate. Given sufﬁ-
cient time, the salt crystals usually precipitate spontaneously. In northern regions,
the low temperatures found in unheated cellars may induce adequately rapid precip-
itation. Where spontaneous precipitation is inadequate, refrigeration often achieves
rapid and satisfactory bitartrate stability.
Because bitartrate crystallization is concentration dependent, mildly unstable
wines may be insufﬁciently stabilized by cold treatment. Protective colloids, such as
yeast mannoproteins, may retard crystallization by masking positively charged sites
on bitartrate crystals (Lubbers et al., 1993). The interaction between tannins, tartrate
and potassium ions also retards crystallization.
Occasionally, crystals of calcium oxalate form in wine. If crystallization occurs, it
develops primarily in older wines because of the slow oxidation of ferrous oxalate to
the unstable ferric form. After dissociation from the metal, oxalic acid may react
with calcium, forming calcium oxalate crystals.
Other potential troublesome sources of crystals are saccharic and mucic acids.
Both are produced by the pathogen Botrytis cinerea and both may form insoluble
calcium salts. Calcium mucate is often the source of yellowish particles occasionally
found in bottles of Sauternes.
Although comparatively rare, the presence of salt crystals is not a legitimate cause
for consumer rejection. The crystals are tasteless and usually remain in the bottle
with any sediment. Alternatively, they adhere to the cork. Because white wines are
transparent and sold in pale to colorless bottles, crystals are more obvious in white
than red wine. In addition, white wines are typically chilled or stored cool, accentu-
ating crystal formation. Some producers mention their possible occurrence by the
euphemistic term “wine diamonds.” Consumers may unwittingly mistake elongated
tartrate crystals for glass slivers.
Resuspension of sediment is probably the most frequent source of clouding in older
red wine. Sediment typically consists of complexes of polymerized anthocyanins,
tannins, proteins, and tartrate crystals. Depending on their chemical composition,
sediment may have a bitter or chalky taste. To some wine critics, the presence of sed-
iment is considered a sign of quality. Excessive and unnecessary clariﬁcation can
remove ﬂavorants, but its avoidance does not guarantee a ﬁner or more ﬂavorful
Although a less common cause of wine rejection than crystal formation, protein
haze can still cause considerable economic loss in bottle returns. Protein haze
results from the clumping of dissolved proteins into light-dispersing particles.
Heating accelerates the process, as does reaction with tannins and trace contami-
nation with metals. Two proteins of importance in haze production in white wine
are pathogenesis-related (PR) proteins—chitinase and an acid-stable thaumatin-like
protein (Waters et al., 1996b). They occur in infected grapes and are also produced
rapidly in grapes damaged during harvesting (Pocock and Waters, 1998). Although
many yeast mannoproteins and grape arabinogalactan–protein complexes may pro-
mote heat-induced protein haze, speciﬁc ones can reduce haze formation (Pellerin
et al., 1994).
Excessive use of oak-chips in wine maturation, or the accidental incorporation
of leaf material from the grape crush (Somers and Ziemelis, 1985) can occa-
sionally induce rare forms of haze. The ﬁrst situation results in the excessive
extraction of ellagic acid, leading to the formation of ﬁne, off-white to fawn-
colored crystals. In the second situation, ﬁne, yellow, quercetin crystals, extracted
from leaf material during crushing, can induce a ﬂavonol haze in white wines
bottled before the crystals have had a chance to settle (Somers and Ziemelis,
1985). The excessive use of sulfur dioxide has also been associated with cases of
phenolic haze in red wines.
Several insoluble metal salts generate haziness in bottled wine (casse). The most
important are induced by iron (Fe3+
) and copper (Cu2+
). The pri-
mary source of troublesome concentrations of these metal ions comes from cor-
roded winery equipment.
Two forms of ferric casse are known. White wines may be affected by a white haze
that forms as soluble ferrous phosphate oxidizes to insoluble ferric phosphate. The
haze results either from particles of ferric phosphate alone, or from a complex
formed between ferric phosphate and soluble proteins. In red wine, oxidation of fer-
rous to ferric ions can generate a blue casse. In this instance, ferric ions form insol-
uble particles with anthocyanins and tannins.
In contrast to iron-induced haziness, copper casse forms only under reduced
(anaerobic) conditions. The casse develops as a ﬁne, reddish-brown deposit when the
redox potential of bottled wine falls during aging. Exposure to light speeds the reac-
tion. The particles consist of cupric and cuprous sulﬁdes, or their complexes with
30 Visual perceptions
proteins. Copper casse is primarily a problem in white wines, but it can occur in rosé
Deposits on bottle surfaces
Occasionally, sediment adheres tightly to glass. This can generate an elongated, ellip-
tical deposit on the lower side of the bottle. Less frequently, a lacquer-like deposit
may coat the interior surfaces of bottles of red wine. It consists of a ﬁlm-like tannin–
anthocyanin–protein complex (Waters et al., 1996a). Champagne bottles may also
develop a thin, ﬁlm-like deposit on their inner surfaces. This phenomenon, called
masque, results from the deposition of a complex between albumin (used as a ﬁning
agent) and fatty acids (probably derived from autolysing yeast cells) (Maujean et al.,
Haze can also result from the action of spoilage organisms (yeasts and bacteria). The
most important spoilage yeasts in bottled wine are species of Zygosaccharomyces
and Brettanomyces. Three groups of bacteria may be involved, lactic acid bacteria,
acetic acid bacteria, and Bacillus species.
Zygosaccharomyces bailii can generate both ﬂocculant and granular deposits
(Rankine and Pilone, 1973), notably in white and rosé wines. Contamination usu-
ally results from growth in improperly cleaned and sterilized bottling equipment. In
contrast, Brettanomyces spp. induces a distinct haziness. It may become evident at
less than 102
cells/ml (Edelényi, 1966). With other yeasts, noticeable cloudiness
begins only at concentrations above 105
cells/ml. Yeast-induced haziness may occur
without spoilage, but frequently it is associated with vinegary (Z. bailii) or mousy
(Brettanomyces) off-odors. Other fungi can cause clouding or pellicle formation,
but only under aerobic conditions—a situation not found in properly sealed bottled
Certain lactic acid bacteria generate a cloudy, viscous deposit in red wines, in a sit-
uation called tourne. The affected wine also turns a dull red-brown, develops a
sauerkrauty or mousy taint, and may show spritz if carbon dioxide accumulates.
Other strains may synthesize profuse amounts of mucilaginous polysaccharides
(b-1,3-glucans). These polysaccharides hold the bacteria together in long silky
chains. The ﬁlaments often appear as ﬂoating threads, generating the condition
called ropiness. When dispersed, the polysaccharides give the wine an oily look and
viscous texture. Although visually unappealing, ropiness is not consistently associ-
ated with taints.
Acetic acid bacteria have long been associated with wine spoilage. For years,
molecular oxygen was thought essential for their growth. It is now known that
quinones (oxidized phenolics) can substitute for oxygen (Aldercreutz, 1986). Thus,
acetic acid bacteria may grow in bottled wine if acceptable electron acceptors are
present. If they multiply in wine, they can form a haziness associated with the
development of marked vinegary odors and tastes. Lactic acid bacteria can induce
a diversity of spoilage problems, usually in wine at high pH values (>3.7). If this
occurs in bottled wine, their growth can lead to the development of a slight
The viscosity of wine is largely a function of its sugar, ethanol, glycerol, and soluble
polysaccharide contents. Usually, though, visually perceptible differences in wine
viscosity are uncommon. If they occur, they tend to result from high sugar and/or
alcohol contents; glycerol contents Ն25 g/l (as in botrytized wines); or the presence
of mucopolysaccharides produced by bacteria (in cases of wines showing ropiness or
Still wines may retain sufﬁcient carbon dioxide after fermentation to form bubbles
along the sides and bottom of the glass. This usually occurs if wine is bottled early,
before the supersaturated carbon dioxide has escaped. Much of the excess, weakly
bound carbon dioxide is soon liberated, and can form bubbles when the bottle is
Bubbles may also come from carbon dioxide produced by bacterial metabolism.
This may develop as a consequence of malolactic fermentation occurring after bot-
tling. It may also result from the action of spoilage bacteria, as in the case of wine
In most instances, effervescence occurs intentionally. The size, association, and
duration of bubbling is an important quality feature in sparkling wines. Slow effer-
vescence is favored by prolonged contact between yeasts (which produce the carbon
dioxide) and the wine. After several months, the yeasts autolyze (self-digest), releas-
ing cell wall constituents (colloidal mannoproteins) into the wine. The weak bonds
formed between carbon dioxide and these proteins are essential to the production of
a steady stream of bubbles following opening.
Many factors affect the solubility of carbon dioxide. Primary among these are
temperature and the wine’s sugar and ethanol contents. Increasing these factors
decreases gas solubility. Once poured, atmospheric pressure becomes the critical
factor promoting bubble formation. Pressure on the wine drops from 6 atm (in the
bottle) to 1 atm (ambient). This reduces carbon dioxide solubility from about
14 g/l to 2 g/l. This initiates the release of approximately 5 l of gas (from a
750 ml bottle). In the absence of agitation, there is insufﬁcient free energy for
to escape immediately. It enters a metastable state from which it is slowly
Carbon dioxide escapes from the wine by several mechanisms (Fig. 2.9). The ini-
tial foaming associated with pouring is activated by free energy liberated by the
32 Visual perceptions
falling wine. Pouring also generates microbubbles that slowly escape. However, the
continuous chains of bubbles, so desired in sparkling wine, are produced by het-
erogenous nucleation. The gas nuclei start to form on rough surfaces of the glass and
suspended particles in the wine. Heterogenous nucleation accounts for about 60% of
released over an hour. In contrast, gushing, the sudden to explosive release
of carbon dioxide, results from a number of separate processes. Mechanical shock
waves or rapid pouring provides sufﬁcient energy to weaken the bonds between water
and carbon dioxide. As the bubbles reach a critical size, they incorporate more CO2
than they lose, and enlarge as they rise. In addition, semistabilized to stabilized
microbubbles, previously generated in the bottle, are ready to enlarge explosively if
sufﬁcient free energy is provided.
Another important feature in assessing the quality of sparkling wines is the accu-
mulation of a small mound of bubbles in the center of the glass (mousse), and a ring
of bubbles (cordon de mousse) along the meniscus at the air–wine–glass interface.
Prolonged duration of the mousse, as in the head on beer, is undesirable. The dura-
bility of these formations is largely dependent on the nature of surfactants, which
decrease surface tension (such as soluble proteins, polyphenols, and polysaccha-
rides). They originate as degradation products of yeast autolysis. Their concentra-
tion in the wine increases two to three times within the ﬁrst year of maturation,
following the second CO2
-producing fermentation. Gravity removes ﬂuid from
between the bubbles, causing them to fuse with one another and take on angular
shapes. As their size increases so does their tendency to break.
After swirling, droplets form and slide down the sides of the glass (Fig. 2.10). These
have variously been termed tears, legs, or rivulets. They form when alcohol evaporates
(slow, continuous, bubble production
desirous in a sparkling wine)
(rapid and excessive bubbling
upon bottle opening)
attaching to rough surfaces
of the glass or suspended
particles in the wine)
(transient generation of sufficient
free energy to induce short-lived
(produced as a consequence
of recent rough handling
of the wine)
(remaining as a consequence
of former agitation
of the wine)
SOURCES OF EFFERVESCENCE
Figure 2.9 Mechanisms of effervescence (CO2
escape) from sparkling wine (from Jackson, 2000, reproduced by permission).