Biochemistry of malting.

Sebree, B.R.

Abstract
Topics discussed in this review include the importance of the grain size grading of the raw barley for homogeneous malt modification (since the time needed to hydrate the endosperm during steeping varies with grain size, in an ungraded batch the small kernels would have a much higher moisture content, and would become much more extensively modified, than the larger ones), the importance of air rests during steeping to allow the saturated embryo to transfer its surplus moisture content to the endosperm, the carbohydrate metabolism of the barley grain during steeping, the activation of enzyme production by gibberellic acid, the progress of modification from the scutellum to the opposite end of the grain, the enzymic hydrolysis of endosperm cell wall pentosans and beta glucans and of the protein matrix surrounding the starch granules, the importance of the precise extent of the last named process (insufficient proteolysis may impede the access of amylolytic enzymes to starch granules during mashing and also results in a shortage of wort amino acids (yeast nutrients) and beer foaming polypeptides, while excessive proteolysis can, among other things, destroy the foam polypeptides), the factors which can influence the isoenzyme composition of amylolytic enzymes (temperature, moisture, pH, etc.), the role of kilning in stabilizing the malt by suspending biochemical activity while simultaneously bringing about various nonbiological chemical reactions which form some flavouring and colouring constituents and the precursors of others, as well as polyphenol oxidation and protein coagulation (which affect the colloidal stability of the beer) and (if precautions are not taken) nitrosamine formation, and the equilibration of the malt moisture content (which at the end of kilning is concentrated in the centre of the endosperm) by storing the malt for at least one week (preferably two) before using it for brewing.
Keywords : biochemistry malting survey