Yeast proteolytic activity during high and low gravity wort fermentations and its effect on head retention

The aim was to discover the effect of high gravity brewing on yeast proteas e activity during fermentation, on the loss of hydrophobic polypeptides fro m wort during fermentation, and on the foam stability of stored beer. The h ydrophobic polypeptide content of low (10 degrees Plato)gravity worts showe d a steady decline throughout fermentation, but for the 20 degrees Plate wo rt there was a rapid decline over the first 8 days of fermentation, followe d by little change over the remaining period. The decrease in hydrophobic p olypeptides was greater in the high gravity fermentation. Proteinase A incr eased during fermentations with the highest levels being present at the end of fermentations. High gravity fermentations exhibited levels of yeast pro tease that from the 3rd to 11th day of fermentation were at least twice the values of the low gravity fermentations, The high gravity brewed beer cont ained significantly higher levels of proteinase A activity than the low gra vity brewed beer. The inclusion of FERMCAP(TM), an antifoam, in high gravit y wort did not affect either the hydrophobic polypeptide levels of foam sta bility of the resultant beer This suggests that proteinase A, rather than f ermenter foaming, must be the major contributor to the lack of foam stabili ty of high gravity brewed beer. Head retention measurements conducted on th e high and low gravity brewed bottled beers, over a five month period, demo nstrated 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 p asteurised.