The aim was to discover the effect of high gravity brewing on yeast protease activity during fermentation, on the loss of hydrophobic polypeptides from wort during fermentation, and on the foam stability ofstored beer. Tlte hydrophobic polypeptide content of low (10°Plato)gravity worts showed a steady decline throughout fermentation, but for the 20°Plato wort there was a rapid decline over the first 8 days offermentation, followed by little change over the remaining period. Vie decrease in hydrophobic polypeptides was greater in the high gravity fermentation.Proteinase A increased during fermentations with the highest levels being present at the end of fermentations. High gravity fermentations exhibited levels of yeast protease thatfrom the 3rd to 11th day offermentation were at least twice the values of the low gravity fermentations. Tlte high gravity brewed beer contained significantly higher levels of proteinase A activity than the low gravity brewed beer. The inclusion ofFERMCAP™, an antifoam, in high gravity wort did not affect either the hydrophobic polypeptide levels or foam stability of the resultant beer. This suggests that proteinase A, rather than fermenter foaming, must be the major contributor to the lack offoam stability of high gravity brewed beer. Head retention measurements conducted on the high and low gravity brewed bottled beers, over a five month period, demonstrated a steady decline in foam stability for both beers. The declines in head retention did not occur in high and low gravity beers that had been pasteurised.
Cells from stationary-phase cultures of two strains of Saccharomyces cerevisiae (3 and 20) failed to flocculate when grown in a complex or a chemically defined medium, while those of two other strains (11 and 13) flocculated when grown in either medium. Strain 30 flocculated when grown in complex but not defined medium and harvested from stationary-phase cultures. pH-electrophoretic mobility measurements on all five strains showed that mobility attributable to carboxyl groups usually increased as cultures progressed from the exponential to the stationary phase, while that caused by phosphate groups tended to decline. Acquisition of flocculating ability was accompanied in strains 11 and 30 by a slight increase in amidase activity, and greater increases compared with nonflocculent populations in activities of leucine aminopeptidase. alpha-mannosidase, and proteinase C. Activities of proteinases A and B showed no correlation with acquisition of flocculating ability.
Our aim was to examine the effect of high gravity brewing on head retention with respect particularly to the effect of high gravity brewing on hydrophobic polypeptide levels. High gravity brewed beer had poorer head retention values when compared to a similarly brewed low gravity beer. Analysis of hydrophobic polypeptide levels in both high gravity wort (20°Plato) and low gravity wort (10s Plato) produced using a lauter tun, revealed that the high gravity wort contained 8% less hydrophobic polypeptide than the low gravity wort (undiluted basis). Analysis of hydrophobic polypeptides throughout the brewing process for these 10°P and 20"P brews demonstrated that the hydrophobic polypeptide content decreased, especially during the kettle boil and fermentation. Furthermore, the high gravity brewed beer suffered the greatest loss, leaving the final beer with approximately 40% less hydrophobic polypeptides than the low gravity beer. Brewing at 10°P and 20"P using a mash filter demonstrated that these filters can improve the head formation and stability of the resultant beers at sales gravity. However, the low gravity beer still produced a more stable foam (Rudin value 93 s) when compared to the high gravity beer (Rudin value 83 s). The mash filter slightly increased the hydrophobic polypeptide extraction. It is concluded that the mash filter produced higher hydrophobic polypeptide levels in the final beers, as well as having a positive effect on reducing the levels of foam negative compounds such as fatty acids in the wort, and therefore slightly improved head retention values.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.