Yukinobu Kano

The production of linoleic and linolenic acid hydroperoxides during mashing

Abstract To clarify the lipid oxidation mechanism during wort production, the production of hydroperoxides during mashing was studied using a chemiluminescence-HPLC method. Free linoleic and linolenic acids increased during mashing and their rates of increase were significantly accelerated at 65°C, indicating that lipase acts during mashing. Linoleic and linolenic acid hydroperoxides increased just after mashing-in, reached a maximum level after 10 min at 65°C, and then decreased. When malt with higher lipoxygenase activity was used or the mashing was started at a lower temperature, the production of both hydroperoxides significantly increased. When an inhibitor of lipoxygenase was added to the mash just before mashing, the production of both hydroperoxides drastically decreased. Therefore, it is suggested that lipoxygenase and lipase in malt plays an important role in the production of linoleic and linolenic acid hydroperoxides during mashing.

Effect of Pitching Yeast and Wort Preparation on Flavor Stability of Beer

Abstract To confirm the role of fermentation conditions on flavor stability of beer and to brew a more stable beer, the effect of several fermentation conditions on the sulfite content in the finished beer and the flavor stability was studied using a pilot scale brewing process. Yeast strain significantly affected the sulfite content, chemiluminenscence (CL) production which serves as an index of the susceptibility of beer to staling, and flavor stability of the resulting beer. Lower dissolved oxygen in pitching wort, higher pitching rate of yeast and clearer pitching wort led to the higher level of sulfite content, the inhibition of CL production, and better flavor stability of the resulting beers. These fermentation conditions did not significantly injure the fermentation process and change the flavor character of the fresh beer with the exception of the yeast strain. It was, therefore, expected that the flavor stability of beer could be controlled by the fermentatiun conditions without harming the fermentation process and the flavor character of the fresh beer.

Role of fermentation conditions on flavor stability of beer

Abstract To clarify the role of wort fermentation conditions on the stability of the resulting beer, the flavor stability of beers brewed at several fermentation temperatures (6–30°C) in a pilot brewing plant (30 l) was studied using chemiluminescence analysis. Chemiluminescence (CL) production in fresh and stored beers increased with fermentation temperatures. Flavor stability of the beers increased with decreasing fermentation temperatures. Sulfite content in the fresh beer decreased with an increase in fermentation temperatures. When sulfite was added to beer, the CL production in beers before and after storage decreased and the flavor stability increased with the concentration of sulfite. These data showed that it was an advantage for beer flavor stability to increase the sulfite level during fermentation. In this pilot study, the CL producing activity had a negative relationship with sulfite content in beer and with flavor stability, indicating that the CL producing pattern of beer is useful indicator for the evaluation of beer stability in the development of a more stable beer.