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Kochi Firms Blend Know-How to Create New Yuzu-Based Tipple

Courtesy of Tosatsuru Sake Brewing Co.
Atsushi Kumeno of Tosatsuru Sake Brewing Co. monitors the fermentation of yuzu juice.

The Yomiuri Shimbun

17:00 JST, April 18, 2023

KOCHI — A sake producer in Yasuda, Kochi Prefecture, succeeded where others had failed in creating a base for a new “hard seltzer” alcoholic beverage, by fermenting the juice of yuzu citrus grown in the prefecture.

A hard seltzer is a type of flavored alcoholic beverage consisting of fizzy water, alcohol and flavoring. It is known for being low in calories and sugar, as well as having a refreshing taste.

Tosatsuru Sake Brewing Co., with help from talented local companies, developed the new beverage, Hakko Yuzu Hard Seltzer no Moto (Fermented yuzu base for hard seltzer), which has an alcohol content of 25%. By mixing the base with carbonated water, customers can enjoy a yuzu-flavored hard seltzer with about 5% alcohol.

Fermenting the yuzu juice reduces the fruit’s bitter and acrid taste. However, the conventional wisdom has been that yuzu juice cannot be fermented.

The brewing company launched its effort in the autumn of 2021, after getting a hint from a competitor’s product that used fermented lemon juice.

Atsushi Kumeno, who studied zymology at Hiroshima University and worked as a chief sake brewer at the firm, began research at the Kochi Prefectural Industrial Technology Center.

But he had difficulties right from the beginning — yuzu juice didn’t ferment at all. Kumeno wondered: “Lemon juice ferments, but why doesn’t the same happen to yuzu juice?”

He continued on, using trial and error, trying about 100 varieties of yeasts and changing temperatures and other conditions. But there was no sign of fermentation.

One day about six months later, Kumeno was discarding yuzu juice, totally at a loss. Then, he saw light from a window being reflected on oil. This made him realize that the fragrant oil components were hindering the juice’s fermentation.

So, he tried to ferment the juice by separating the oil components, but a new problem emerged. When the juice was heated up to more than 80 C to evaporate the oil components, the juice’s taste was damaged.

The prefecture’s industrial technology center introduced Kumeno to the microwave extracting equipment of Kanematsu Engineering Co. in Kochi City. The equipment made it possible to make oil components evaporate at about 40 C. By removing the oil components in an ideal condition, Kumeno finally succeeded in fermenting the yuzu juice.

Then he hit another wall, when he tried to put the fragrant oil components back into the fermented juice. They didn’t mingle well.

To solve the problem, a machine developed by Sakamoto Giken Co. and National Institute of Technology, Kochi College, both in Nangoku in the prefecture, proved useful.

An application of what is called fine-bubble technology made it possible to “chop up” the oil components to a size less than 0.1 millimeter by producing ultrafast swirls. As a result, it became possible to blend the oils back into the juice.

In February, the brewing company put on sale 430 bottles of fermented yuzu juice blended into the base of self-manufactured craft spirits. Through crowdfunding, they also solicited donations for the product’s future production. The beverage sold out in a few days.

The company plans to start selling the beverage to the general public in May. If it receives good customer responses, the firm may consider mass production. A 500-millimeter bottle is expected to be priced at ¥2,035, including tax.