Some practical aspects of malting and mashing related to yeast nutrition and fermentation.
Phytin exists in barley as soluble K and Na salts. During malting, phytase is produced and initiates the breakdown of phytin to orthophosphate and mesoinositol, an essential yeast growth factor. Some of the phosphate passes to the rootlet and by restricting vegetative growth this loss is minimized. Ca and Mg salts in steep water and the possible addition of bisulphite of lime react to form insoluble salts of phytin which are not available for enzyme attack in the mash tun. Optimum mash conditions for phytase action are pH 5.2 and 48 degrees C. Insoluble phytin salts are formed with Ca so excessive addition of gypsum to the mash can restrict the amount of inositol and soluble phosphates in the wort. During mashing the nucleoproteins of malt go into solution with release of free nucleic acid but this reacts with Ca to form insoluble material which cannot be hydrolysed so an excess of hardening in mash liquor should be avoided. Nucleophosphate enzymes liberate phosphoric acid, ribose and the purine and pyrimidine bases which are essential material for the synthesis of yeast nucleic acid and enzymes. The nucleotidase which splits off phosphate from the nucleotides has optimum activity at pH 5.6 and 50 degrees C so is active in the mash but nucleosidase which breaks down nucleosides to ribose and the range of bases has a much lower optimum temperature and is restricted in the mash tun so that wort contains nucleic acid with a mixture of breakdown products. Excess of gypsum in the mash gives insoluble salts of phytin, nucleic acid and nucleotides depriving the wort of bios and yeast nutrients. It is better to lower mash pH with mineral acid to secure the fullest degradation and to add gypsum to the copper to remove unreacted phytin and nucleic acid which might precipitate during fermentation or later give rise to beer haze.
Keywords: brewing fermentation malting mashing nutrient survey yeast