O-27. Reducing fermentation variation

Presenter: Peter Bouckaert, New Belgium Brewing Co., Fort Collins, CO.

Fermentation time and temperature profile consistency are important to produce consistent beer. This study focuses on fermentation time consistency. The aim of the work was to reduce the standard deviation of fermentation time by a factor 3. Most work was done on ale fermentations and then later applied to the lager fermentations within this brewery. Screening of the relative importance of different variables affecting fermentation time was initially done through modeling of existing fermentation data. Models gave a better fit (r2) when yeast vitality data from the previous fermentation and yeast storage were used instead of current fermentation data such as yeast count and methylene blue viability. Yeast vitality was quantified through the heat-up rate of the fermentation, length of the fermentation, and cool-down rate of the previous fermentation and yeast storage time. The key variable for predicting fermentation time was the rate of temperature increase in the fermenter. The most important parameter to control heat-up rate was found to be the temperature in the fermenter during filling. Other variables and interactions between variables were previous fermentation time and heat-up rate, cool-down rate of previous fermentation, yeast storage time, pitching rate, and (more for lagers) temperature of the environment. Two full factorial (two levels) designed experiment on knock-out temperature and pitching rate showed that pitching rate could be used to reduce the standard deviation of fermentation time within the range tested. Variables affecting vitality were addressed in a couple of different ways. Cool-down rate of fermentations was resolved by reserving fermenters with high variability in cooling for aging only. Yeast storage time was addressed by guidelines, a limited amount of yeast storage tanks, and monitored. Fermentation time and heat-up rate became less variable in this process. Outliers for the latter parameters were used as yeast harvest selection criteria.

Peter Bouckaert studied biochemical engineering, with specialization in brewing and fermentation technology, in Ghent, Belgium. He was brewmaster for nine years at the Rodenbach brewery, worked in the Kronenbourg and De Gouden Boom breweries, and was involved with some distilleries, all in Belgium. He started his own brewpub, De Zwingel, in 1994. In 1996 Peter changed course and became brewmaster in New Belgium Brewing Co. in Fort Collins, CO.

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