Low-temperature fermentation of high-gravity wort.

Takahashi, S., Ishibashi, T., Hashimoto, N. and Kimura, Y.

Abstract
Because, other things being equal, brewers' yeast proliferates more slowly and consumes less alpha amino nitrogen when fermenting higher gravity worts, breweries which practise high gravity brewing often raise the fermentation temperature to stimulate the yeast, which accelerates nitrogen uptake, cell growth and budding but also causes an increase in the formation of certain flavour active fermentation by-products, producing a beer which is often quite different in flavour from that produced by the same yeast strain from a normal gravity wort of otherwise identical composition. The results of low temperature pilot scale fermentation trials of a high gravity (15 degrees P) wort are described. It was found that although the order of consumption of the different wort amino acids by the yeast was not affected by wort gravity, the quantities of phenylalanine, valine and especially alanine taken up from the high gravity wort were smaller than the amounts of these amino acids taken up by the same yeast from a medium gravity (11 degrees P) control wort. Ester production increased, but higher alcohol production remained relatively low. Diacetyl formation was also fairly low, and it was also found that diacetyl removal during maturation was more rapid in the high gravity brewed beer than in the control. When tasted, the finished beer from the high gravity process was found to have a mild flavour, with malty, estery and sweet flavour notes and a full bodied mouthfeel. Unlike some other high gravity brewed beers described in the literature, in which the estery flavour was unpleasantly strong, the intensity of the estery flavour of this beer, though quite perceptible, was low enough to have a positive rather than negative effect on the overall flavour quality, which the taste panel considered to be excellent.
Keywords : beer fermentation flavour high gravity brewing quality temperature