Barley and malt are rich in vitamins and are localized in the living tissues of the embryo and of the aleurone layer. They are involved in building enzymes as part of a prosthetic group. Of the vitamins in the B complex, vitamin B1 is present in barley in amounts ranging from 1.2–7.4 mg/kg barley, dry matter. During germination, the concentration of vitamin B2 increases to 1.5 times the quantity found in barley. This corresponds to a concentration of 1–3.7 mg/kg malt, dry matter.
Aside from numerous other active organic substances, vitamins are also necessary for yeast during reproduction and fermentation. Paramount among these vitamins is thiamine (vitamin B
1), riboflavin (vitamin B
2), niacin (vitamin B
3), pantothenic acid (vitamin B
5), pyridoxine (vitamin B
6), biotin (vitamin H) and inositol. Organic growth promoters serve as functional metabolic building blocks, which allow cellular enzymes to be effective. Niacin is a component of coenzyme I, which transfers hydrogen in the phosphoglyceraldehyde dehydrogenase system during cell metabolism. Niacin is present in the form of nicotinamide, while pantothenic acid is a constituent of coenzyme A, which is vital for carbohydrate metabolism.
Pyridoxal 5’-phosphate is the active coenzyme of pyridoxine and of great significance for amino acid metabolism. In addition to biotin, which plays an important role in yeast growth and serves as a coenzyme in all ATP-dependent carboxylation reactions, thiamine and riboflavin promote yeast metabolism. Thiamin as the coenzyme for carboxylase is central to carbohydrate metabolism. Riboflavin, in the form of flavin mononucleotide, participates in oxidation-reduction reactions in the prosthetic group of dehydrogenases. Beer only contains small amounts of thiamine. However, brewing yeast is rich in thiamine, as it is very rapidly taken up by yeast from the wort. In contrast, greater quantities of riboflavin are present in beer, since this enzyme, as described above, is affected by the malting process and is primarily derived from malt. The yeast absorbs only relatively small quantities of riboflavin during fermentation.
Riboflavin supports a number of processes, which increase the rate of aging in beer, because the Strecker degradation reaction is promoted by the photooxidation of riboflavin. This results in an increase in volatile substances, among them a large number of long-chain, and in part unsaturated, carbonyl compounds primarily attributable to off-flavors associated with aging in beer. Analogous to Strecker degradation, the oxidation of higher alcohols through the influence of light in the presence of riboflavin occurs more rapidly. Oxidation reactions in the side chains of iso-humulones are also accelerated in the presence of light and riboflavin. Photoactivation of riboflavin leads to the formation of carbonyl compounds and mercaptans. The compound responsible for the lightstruck flavor (3-methyl 2-butene 1-thiol) is created along with numerous other mercaptans. However, riboflavin slows the auto-oxidation of long-chain fatty acids into shorter-chain aldehydes.
The B vitamins are abundant in beer. In addition to vitamins B1, B2 and B6, the substances biotin, niacin, folic acid and pantothenic acid can also be found.
show less