Yeast Nutritional Requirements
All-malt worts typically have an adequate supply of adequate supply of nutrients—fermentable carbohydrates, nitrogen sources, vitamins, and minerals—for healthy fermentation. These nutrients are naturally present in malted barley or developed by enzymes during the malting and mashing process. All these nutrients are required to produce new proteins and enzymes that will help the yeast cells grow, divide, and conduct alcoholic fermentation.
Carbohydrates are one of the biggest classes of macronutrients for yeast which include monosaccharides glucose and fructose; disaccharides sucrose and maltose; and the trisaccharide maltotriose; and nonfermentable carbohydrates (limit dextrins). Brewing yeast strains (Saccharomyces cerevisiae and S. pastorianus) can typically utilize sucrose, glucose, fructose, maltose, and maltotriose (preference for that order) (Layfield et al., 2015).
The other major nutrient class affecting brewing yeast performance is nitrogenous compounds. Nitrogenous constituents of wort influence healthy yeast growth and development as well as affect haze formation, head retention, and the biological stability of beer. Nitrogen is available for yeast growth in wort as amino acids, peptides, and ammonium salts. Yeast prefers to use ammonium salts, but these are present in wort only in very small amounts (Kunze, 1996).
Brewer’s wort is a rich source of vitamins and contains biotin, thiamine (B1), pantothenic acid, nicotinic acid, riboflavin, inositol and pyridoxine, pyridoxal and pyridoxamine. Most brewer’s yeast has an absolute requirement for biotin and many requires pantothenic acid. Biotin is obtained from malt during mashing and is involved in carboxylation of pyruvic acid, nucleic synthesis, protein synthesis, and synthesis of fatty acids.
Yeasts are unable to grow unless provided with a source of a number of minerals. These include phosphate, potassium, magnesium, calcium, sulfur, and trace elements such as zinc. Enzymatic reactions use minerals as co-factors. Minerals facilitate the cell uptake of materials, and yeast use minerals in cell structural material. Phosphate is involved in energy conservation, is necessary for rapid yeast growth, and is part of many organic compounds in the yeast cell. Potassium ions are necessary for the uptake of phosphate.
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