Like Tobias said, corn is made mostly of starch and lack any enzymes which can convert the starch to fermentable sugars.
Since you are asking for stove top, I am going to assume DME/LME and the corn will just be your adjunct. However, if you are just going for corn, you will just need a lot of it.
So back to your question! Yes, you can does this on stove top, and I suggest the Brew In A Bag method (BIAB). Get one of these Grain Bags, but one big enough to fill the pot you will be mashing in. If you have a all metal oven capable pot, this will be easier as well.
To break down the corn starches into sugars, you will need to gelatinize the starches performing a Cereal mash and then you will need Amylase Enzyme to convert the starches into sugars. Easiest way to get that is to also mash a grain that is high in amylase, either domestic 2-row or domestic 6-row. For a corn beer either is fine, but styles lean ale 2-row and lager 6-row.
How much grain do I need? You will need 50% of total corn weight in grain. So 5lbs of corn you will need 2.5lbs of 6-row + the grain for your cereal mash. See below.
How much grain do you need for the cereal mash? Aim for 20% of the total corn weight. So if you plan to mash 5lbs of corn, get 1lb of domestic 6-row this step.
You may skip the Cereal Mash if you get Flaked Maze. You can pick it up at a homebrew shop and it just makes things a bit easier for you.
What about the corn? You can use fresh corn, and all you really need to do is cut it off the cob and give it a good squish. Dry corn needs to be milled, a Corona/Cereal Mill can usually handle that, but a homebrew shop mill would be better. Remember to mill your grain as well.
The Cereal Mash
Heat up 2qts of water per pound of corn/grain going into the cereal mash to 158d^F
Take your corn and 20% grain and throw it all into the pot.
Steep for 15 minutes at this temp.
Then bring the cereal mash up to a gentle boil for 20-30 min.
Stir the cereal mash constantly so it does not scorch.
The cereal mash is done when the mash breaks down and coats the back of your spoon.
Take your pot, and fill it up with 2qt per 1lb of corn/grain you are going to use.
Fill the grain bag with your grain and cereal mash and place it in the pot. Heat it up to 140d^F for an 30min-hour depending on how dry you want the beer to be.
Raise the temp to 150d^F
Cover and maintain the temp for an hour. I have had to wait 1.5 hours before, just because there was so much startch, and not enough amylase. Just depends on how big you want to go ABV wise.
Raise the temp again to 168d^F for 5minutes
Take a gravity reading to see where you are.
If you have a oven, you can set the oven for the desired temp and put the entire pot in there for each step.
When the mash is done.
Uncover and swirl the bag around the wort for a minute or two.
Then lift the bag out and let it drain into the pot. Dont squeeze the bag or you will get tannins and lots of protein.
Put the bag back in the pot.
Repeat steps 1-3 three to five times, on the last time just let the bag drain and then throw it away.
At this point add your DME/LME in to the pot if you have any.
Boil for 90min at a vigorous boil. This is especially important with this kind of beer to avoid dimethyl sulfide (DMS)
Use a good neutral hop like Saaz and Hallertau and aim for 10-15IBUs.
Pick a lager yeast of your choice and let it go!
Hope this helps.
USING ONLY CORN TO PRODUCE ENZYME
The answer is, YES and NO and it depends on the path you take when fermenting corn. There are several things that must be addressed. I too had mixed understandings throughout the years. Only recently have I come to have a better understanding.
- A dry, mature kernel of corn, that has not been sprouted, contains a "starch sac" called endosperm and the embryo.
- For the embryo to develop (germinate .... sprout), the embryo must have food in the form of simple sugar.
The only way for the embryo to sprout into a plant is for the starch in the kernel to be converted to sugar and this takes enzymes (malt).
Dry, mature corn (shelled or dry and still on the cob) contains no enzymes which are required to convert starch to sugar but dry mature corn possesses the ability to make its own enzyme under proper conditions.
- An enzyme is a protein that nature has designed. An enzyme is an organic catalyst that drastically accelerate a chemical reaction without ever being consumed during the reaction. An organic catalyst differs from an inorganic catalyst in various ways but the following sentence is only important to understand. An organic enzyme is a protein, and because a protein is heat sensitive, not too much heat can be used when converting starch to sugar or you WILL destroy your enzyme and conversion will immediately slow to a crawl. Hence, when converting starch to sugar, care must be taken not to exceed 150F.
The following is where "the tree forks" and often confuses individuals when addressing the issue of fermenting corn.
Let's start with fermenting cracked corn
- Cracked corn is dry, mature kernel corn that has been cracked into 6 or 8 pieces. For example "chicken scratch" is cracked corn.
- The vast majority of cracked corn (by weight) is starch.
- Starch cannot be "eaten" by the type of yeast we use.
- Starch is long repeating chains of simple sugars that are connected chemically.
- Before yeast can "eat" the simple sugars found in starch, the connecting chemical bonds of simple sugars that create starch must be broken in order to release all available simple sugar molecules for consumption by yeast. This is often called "conversion".
- Before this converting process begins, corn (or even ground corn meal) must be gelatinized, i.e. cooked to soften the corn to a gelatin consistency. This will provide a greater surface area for enzymes to react and speed the process of conversion. It is important to note that starch does not dissolve in water therefore starch cannot be broken down into simple sugars by simply attempting to dissolve corn meal, cracked corn, or corn starch in water (be it hot or cold).
NOTE Cooking corn meal alone does not convert starch to sugar. Cooking will, however, cause number and size of highly organized crystalline starch regions to decrease leading to random, unorganized crystalline regions of starch. Broken hydrogen bonds create space in the crystalline structure thus allowing water to enter the space created by hydrolysis which in turn results in starch gelatinization. In no way has this converted polysaccharides to simple sugars but gelatinization improves the availability of starch for amylase hydrolysis (break down of available starch to simple sugar in the presence of an appropriate enzyme).
- Once cracked corn (or corn meal) has been cooked (gelatinized) this "gelatinous mess" is ready for conversion.
- As previously stated, conversion takes place in the presence of enzymes. Starches cannot be broken down to sugar without enzymes. If you choose to use grain as malt (little enzyme factories) rather than "store bought stuff" then you must prepare the grain and turn each kernel into an "enzyme factory".
- Malt is best produced using Barley because it contains many different enzymes that will convert starch to sugar but for the sake of answering the question I will stick with corn. By soaking or wetting shelled corn for several days, each kernel will begin to swell. Soaking or wetting fools each kernel into believing that it's growing season.
- Under the right conditions (water, warmth, and light) the miracle of life begins. Miraculously, Mother Nature devised a marvelous but complicated means for the tiny embryo to burst forth into life. Remember, I stated earlier that the tiny corn embryo needs simple sugars to develop and grow but all the sugar that's contained in the kernel is bound up as starch. The embryo cannot survive without food (simple sugar) and will surely die.
- So, in the presence of all the right conditions, the little embryo begins to manufacture enzymes that leak into the starch sac and break down the starch to sugar so it will have the energy to grow and poke it head through the soil. Once the embryo grows into a young plant and makes it to the surface, all the starch in the kernel will have been converted and consumed and sunlight and nutrients in the soil and water will provide for the plant's remaining days on earth. The umbilical chord is severed when the plant makes it to the surface.
- Now, what we want to do is capture the manufacture of enzymes in the kernel just at the right time thus capitalizing on the maximum enzyme level. If you wait too long, the embryo will have used all enzymes and starches to break free of its shell.
- When little "roots" develop at the end of each kernel of corn (approximately 1/4" long) enzyme levels are said to have reached the maximum level. It is at this time you wash the "sprouting corn", remove the little roots and "hair", grind the corn and toss it into your pot that contains gelatinized starch (cooked cracked corn or corn meal).
- When the ground malt is added to your cooked corn, you will need to elevate the temperature of your mix to between 140F and 150F degrees. Conversely, if the malt is ready and you have just finished cooking the corn, then lower the temperature of the cooked corn to 140F to 150F degrees before adding the malt. Remember, enzymes are a protein and can be easily destroyed by heat.
- After holding the mixture's temperature between 140F and 150F for 40 to 60 minutes, conversion from starch to sugar should be complete.
- Conversion can be verified by removing a small amount of "converted mix" and placing it on a saucer and adding a drop of iodine. If starch is still present the sample will turn blue and the mix will require a little more heating time. If conversion is complete there will be no blue color.
- Assuming conversion is complete, lower the temperature of the mix to around 80F degrees and toss in the yeast.
Fermenting sprouted corn
Sprouted corn will ferment if you stop germination at the appropriate time. Remember, you want to keep the embryo from eating all the sugar that has been converted. If you allow the sprouts to get longer than the kernel of corn or greater that 1/4", then you are losing sugar which is what the yeast needs in order to make ETOH.
When your sack(s) of corn has/have begun to sprout, wash the corn, remove roots & hair, and grind into a mush. Heat the mush for 40 to 60 minutes between 140F and 150F, cool to 80F to 85F degrees and then add yeast and allow to ferment.
NOTE: The reason you heat the malt and corn mix to between 140F and 150F degrees is to speed up the chemical conversion from starch to sugar in the presence of a catalyst. In theory, if you did not use heat, the reaction would still go to completion ...... but it would take much longer.
What I am about to say is purely academic and for your personal edification. With regard to organic catalyst or inorganic catalyst, I've already stated that a catalyst is used to accelerate a chemical reaction and the catalyst is not consumed during a chemical reaction. This means that as soon as the catalyst has been used to accelerate and complete a chemical reaction, it is released to be used again and again and again. So sometimes not much catalyst is necessary.
It should be interesting to point out that there is an unspoken truism in the above paragraph. Since a catalyst is used to accelerate a chemical reaction, then it's reasonable to assume that in the absence of a catalyst the chemical reaction will still go to completion but at a far slower rate. And this is true. Some complex chemical reactions may occur in the "blink of an eye" when accelerated by a catalyst but in the absence of the catalyst, the reaction may take years or even hundreds of years to go to completion.