Brewing Yeast Nutritional RequirementsMay 17, 2012 # 9:28 PM # Brewing Chemistry # 4 Comments
The brewing yeast will be growth successfully and good vitality if adequate supply of nutrients, fermentable sugar, amino acid, vitamins and minerals. These nutrients are always enough in wort that it is not limiting the growth of yeast.
Carbohydrates (Carbon source)
Low molecular weight sugars such as glucose, fructose, maltose, sucrose and maltotriose are available for yeast growth. The bigger carbohydrates (such as dextrose) are not used by the yeast cell. The wort consists about 80% of fermentable extract. The other 20% consists of non fermentable products such as dextrose, beta-glucans, pentosans, and oligosaccharides.
Amino Acid (Nitrogen source)
The yeast cells used amino acid to synthesize more amino acids and, in turn, to synthesize proteins. Amino acids collectively referred to as “free amino nitrogen (FAN),” are the principal nitrogen source in wort and are an essential component of yeast nutrition. Three groups of essential amino acid are following…
Group A: this group will fastest taken by the yeast cell in the beginning of fermentation, but synthesized later e.g. Aspartic acid, Asparagin, Glutamic acid, Glutamine, Threonine, Serine, Methionine.
Group B: the yeast cell will be synthesis at early stages of fermentation, but prevented later e.g. Isoleucine, Valine, Phenylalanine, Glycine, Alanine and Tyrosine.
Group C: these amino acids the yeast cell only taken from wort, it’s can not synthesized it owns e.g. Lysine, Histidine, Arginine and Leucine.
Vitamins such as Choline, Thiamin (B1), Folic acid, Nicotinic acid, Calcium pantothenate, Pyridoxin and Biotin are essential for enzyme function and yeast growth. These vitamins always enough in wort that it is not limiting the growth
of yeast. In wine and cider production you may have to add nitrogen containing salts (e.g. ammonium phosphate), some times even thiamine and riboflavin.
The yeast cells are unable to grow unless provided with a source of essential minerals. These include P, K, Ca, Mg, S and trace elements. For example phosphate (P) is involved in energy conservation, is necessary for rapid yeast growth, and is part of many organic compounds in the yeast cell.
Zinc (Zn) is the most important trace element is zinc, the optimum content should be 0.15 ppm. Need of zinc depends largely on yeast strain, some yeast strain may need even more zinc and therefore some breweries add it to wort. Zinc assists in protein synthesis in yeast cells and controls their nucleic acid and carbohydrate metabolism. Also, it very important for stabilisation of proteins and membrane systems, activity of enzymes, protection of enzymes against denaturation, speeding up riboflavin synthesis, stimulation of sugar uptake. Zinc may reduce enzyme activity in mashing. High level poisonous, but seldom. To increase zinc level you can theoretically select proper malt, higher malt modification, lower mash pH, lower mashing in temperatures, shorter mashing times, use low mash concentrations and use some amount of husk or spent grain extracts.