Fermentation Symposium�Part II Accelerated Fermentation of High-Gravity Worts and Its Effect on Yeast Performance.

Fern�ndez, S., Machuca, N., Gonz�lez, M.G., and Sierra, J.A.

Abstract
Brewery worts of 16, 18, and 20� P were fermented with two yeast strains (J-3015 and J-2036), at three temperature programs (initial temperature of 10�C and maximum temperatures of 16, 18, and 20�C). The attenuation curves were normal with the three wort gravities. The pitching rate had to be increased proportionally to the increase in gravity. The percent of dead cells in the yeast collected after each fermentation was proportional to the gravity of the wort, and this effect was more pronounced when the yeasts were in contact with beers with an alcohol content above 4% by weight at high temperatures (18�20�C). The collected yeast was used in subsequent fermentations, adjusting the pitching rate to compensate for the percent of dead cells. The total vicinal diketone (VDK) curves were different, with strain J-3015 producing higher levels of VDK precursors during fermentation when a maximum temperature of 16�C was used. Both strains showed a tendency to produce lower levels of total VDK as the maximum temperature of fermentation was raised to 20�C.
Keywords: Diacetyl-reducing activity, Fermentation temperature, High-gravity brewing, Yeast viability