Relationships between beer characteristics and the diacetyl and pentanedione content of top-fermented beers.
Multiple and simple correlation of coefficients between an independent and a dependent variable (e.g. diatyl) were calculated by stepwise multiple regression analysis, results being expressed as multiple determination coefficients (DC = rm2 x 100). Relations were examined between beer diacetyl and pentanedione and beer properties grouped under (a) conventional (b) amino acids, vitamins and miners; and (c) fermentation by-products. Of (a) pH, viscosity, dissolved carbon dioxide, dissolved O2and coagulable N were closely related to diacetyl content. Of (b) and (c), iron, sodium, thiamine, pyruvate, glycerol, ethyl acetate, acetoin, acetaldehyde, the pentanols and isobutanol, but not amino acids, showed high DCs. When all analysed constituents were combined as 'total properties', 95% of the diacetyl was attributable to pyruvate (49.0%), sodium (29.0%), acetate (10.4%), acetaldehyde (-4.5%) and manganese (-2.7%) and 95% of the pentanedione content to sodium (41.4%), malate (31.4%), pyruvate (11.9%), coagulable N (5.2%), hop bitter substances (4.2%) and pantothenate (4.3%). The biochemical basis of these findings is briefly explained. Using a summation of values for diacetyl and pentanedione to indicate correlations between vicinal diketones (VDK) and beer properties, high values of DC were obtained in (a) for anthocyanogens, coagulable N, pH, viscosity and dissolved carbon dioxide. In group (b) amino acids again gave insignificant values, but high values were obtained for sodium, iron, thiamine, pantothenate and biotin, and for pyruvate, glycerol, acetate, ethyl acetate, acetoin and isoamyl acetate in group (c). In the group of total properties, 95% of the VDK level was attributable to pyruvate (36.9%), sodium (33.8%), pantothenate (14.15) and hop bitters (12.0%), all four properties showing positive coefficients. The practical conclusions are that (1) primary and secondary fermentations should be manged so that, in the active phase, yeast forms low concentrations of pyruvate, malate acetate and acetaldehyde, low acetohydroxy acids and later absorbs these products; and (2) the final beer should be free from acetohydroxy acids and have low contents of pyruvate, malate, acetaldehyde, sodium and manganese.
Keywords: beer chemical composition correlation analysis diacetyl fermentation