Fermentation Symposium—Part II Accelerated Fermentation of High-Gravity Worts and Its Effect on Yeast Performance.
Fernández, S., Machuca, N., González, M.G., and Sierra, J.A.
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