J. Inst. Brew. vol.108:4 (2002) The Loss of Hydrophobic Polypeptides during Fermentation and Conditioning of High Gravity and Low Gravity Brewed Beer

The Loss of Hydrophobic Polypeptides during Fermentation and Conditioning of High Gravity and Low Gravity Brewed Beer

S.E. Brey, ¹, ² J.H. Bryce ¹ and G.G. Stewart ¹
¹International Centre for Brewing and Distilling, Heriot-Watt University, Edinburgh, EH14 4AS, Scotland.
²Corresponding author. E-mail: S.E.Brey@hw.ac.uk

J. Inst. Brew. 108(4), 424-433, 2002 | VIEW ARTICLE

ABSTRACT
The object of this study was to investigate the loss of hydrophobic polypeptides, which are important for foam quality and stability in finished beer. Loss of hydrophobic polypeptide due to fermenter foaming occurs during transfer of fermented wort since a gradient of hydrophobic polypeptides towards the surface is created during fermentation. Due to higher polyphenol levels in high gravity (20°Plato) wort, more hydrophobic polypeptides are lost due to cold break (cold trub) precipitation compared to low gravity (12°Plato) wort. Another important factor affecting the loss of hydrophobic polypeptides could be proteinase A activity during fermentation, especially in high gravity fermentation where the yeast is exposed the higher stress. During high gravity fermentation, where osmotic pressures are higher, ethanol levels become greater, and nitrogen-carbohydrate ratios are lower, more proteinase A is released by the yeast. This release of proteinase A into fermenting wort could have implications for the foam stability of the finished product.

Key words:
Cold break, foam stability, high gravity brewing, hydrophobic polypeptides, proteinase A.