The effect of proteinase A on foam-active polypeptides during high and low gravity fermentation.

The ability of beer to produce good foam is influenced by the level of foam-active polypeptides. Specific polypeptides with hydrophobic domains, such as Lipid Transfer Protein (LTP1), are important components of beer foam. Although, high gravity brewing is a commercially viable technique, it has the disadvantage of producing beer with less foam stability compared to lower gravity brewed counterparts. It is thought that proteinase A plays a key role in the degradation of these hydrophobic polypeptides responsible the beer foam stability. The object of this study was to compare and quantify the loss of hydrophobic polypeptides and specifically foam-LTP1 during high gravity (20°Plato) and low gravity. (12°Plato) wort fermentations and to evaluate the effect of proteinase A on these polypeptides. The losses of hydrophobic polypeptides and foam-LTP1 were generally greater in high gravity brews. Furthermore, the results obtained suggest that proteinase A alters the hydrophobicity of these polypeptides rather than their molecular size. Approximately 20% of hydrophobic polypeptides and approximately 57% of foam-LTP1 appeared to be proteinase A resistant. These differential losses of hydrophobic polypeptide and foam-LTP1 could have implications for the foam stability of the finished product.