Bacteria, Not Just Brewers, Make the Sake

It is commonly thought that alcohol actually kills off bacteria, and in some cases this is true. However, microbes are also an instrumental part of the alcohol brewing processes, as proven by a recent study of a sake brewing facility.

Sake is a traditional Japanese rice wine that is served either hot or cold, depending on the meal and the type of sake. Much like European wine comes from fermented grapes, sake is made in a three-part brewing process using rice grain.

According to a study accepted for publication in the journal Applied and Environmental Microbiology, the prevalence of specific bacterial and fungal organisms is paramount in each of these three stages, and appears to be what truly facilitates the brewing of a good sake.

Co-author David A. Mills from the University of California, Davis, says that brewers have long known that microbes help facilitate their brewing, taking certain steps to encourage their inclusion. In the case of the studied sake facility, for instance, the brewers restrict inoculation to yeast and a single species.

"The kojii fermentation is dominated by an inoculated fungus, Aspergillus oryzae, which helps process the rice into smaller, more available sugars," mills explained in a statement. "The Kojii is then diluted with steamed rice and water to form the seed mash or moto. In this stage the alcoholic fermentation commences with yeast and various lactic acid-producing bacteria populations expanding."

According to Mills, this next stage is when local bacteria population start to play a role.

"Bacillus, Staphylococcus, Lactobacillus - they all consume available nutrients and stabilize the product."

Close analysis of the brewing facility found that these microbes - with the exception of A. oryzae - actually came from the facility's surfaces, suggesting that it is the local microbiome that helps facilitate necessary fermentation, and may vary from region to region.

"Thus, the environmental conditions are important for controlling these fermentations," said Mills.

This could imply that the brewery, not just the brewer, makes a good sake.

Mills hopes that this kind of ecological understanding will one day help ensure and improve food quality across the board.

A manuscript of the study, slated for a September release, was provided by the American Society for Microbiology (ASM).