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​8. Heterogeneous fermentation method in multi-filling cylindroconical vessels for high quality beer

Yuichi Nakamura, Asahi breweries, LTD.

 

ABSTRACT: According to the results of our previous report, the impact of the wort aeration period of multi-filling CCVs, presented at Brewing Summit 2010, we changed the ways to pitch yeast and aerate wort. In our breweries, four batches of wort are filled in a 5,000 hL cylindroconical vessel. In the process before the change, the same amount of yeast and air were pitched into the first to fourth batches of wort. As for the improved process, yeast and air were pitched into the first, second, and third worts, while neither yeast nor air was injected into the fourth wort, which was just transferred to the fermentation vessel. Though this improvement raised the sensory scores as expected, the specific gravity and the number of yeast cells of the fermenting beer were largely different from the data before improvement. Therefore, we developed new equipment capable of sampling the fermenting beer at four different heights in a fermentation tank and installed it on the 5,000 hL tank in our brewery. (Detailed specifications of the equipment are separately reported by our colleague Hisao Koizumi.) Under the previous conditions, the temperature, yeast cells, specific gravity, and amino nitrogen of the fermenting beer were the same at all four different heights. In the case of the improved method, the bottommost layer and the upper three layers of the fermenting beer were not blended, and fermentation proceeded as each layer remained independent. After 50–60 hr from initiation of fermentation, convection was generated, and the 5,000 hL of fermenting beer became homogeneous. At the time just before the fermenting beer was blended, the bottommost layer contained a rich amount of remaining amino acids and monosaccharides. Meanwhile, these amino acids and monosaccharides had already been consumed and depleted in the upper three layers. When the entire fermenting beer in the fermentation vessel was blended after 50–60 hr of fermentation, the nutrients remaining in the bottommost layer, such as amino acids and monosaccharides, were supplied to the upper layers. According to the flow cytometry results on yeast budding, the bottommost layer beer before blending contained a larger percentage of currently budding yeast cells. These results suggested that the bottommost layer beer contained many yeast cells under nutrient-rich conditions that were highly active and currently budding, and such highly active yeast cells were then diffused throughout the entire fermentation tank at approximately 50–60 hr. We therefore concluded that fermentation steadily proceeded to the end without reducing the rate, and thus the beer flavor and taste were improved and stabilized.