CULTURE

While we can't determine the exact origin of yimyu in Taiwan, the operation of certain yimyu breweries into their fifth or sixth generation of owners suggests that Taiwanese yimyu has been around for at least a century.

Today, Taiwanese yimyu can be categorized into five major brewing styles, resulting in a flavor profile even more diverse than that of Japan. As an island nation with a culture built on migration, Taiwan inherited yimyu from China – but its production methods have been influenced by Taiwan's local climate and Japan's soy sauce-making techniques.

It's said that yimyu was first introduced to the island during the Koxinga Dynasty. While Chinese soy sauce was universally made with yellow soybeans, Taiwan's yimyu relied on black soybeans as its main ingredient. During the koji inoculation process, rice bran was added to increase the fermentation surface area, and the process also involved a step known as 'yim.' This suggests that Chinese soy sauce underwent at least one stage of localization in Taiwan.

Through archival research, I discovered that Taiwan's dry fermentation method for making yimyu is almost identical to the process of making Fujian's Guantou soy sauce. The main differences between the two lie in their fermentation vessels and methods: with the Guantou method, the inoculated soybean koji is placed in wooden barrels for fermentation, without exposure to sunlight. By contrast, when making Taiwanese yimyu, the koji is sealed in earthenware jars which are then exposed to the sun for fermentation.

Both methods employ either black or yellow soybeans; however, historical records provide clear evidence that black soybeans were preferred in Taiwan for making soy sauce. According to The General History of Taiwan, Volume 27, "Black soybeans are sown in April or May and harvested in August or September. They produce a particularly sweet soy sauce and are also used for yanchi (fermented black soybeans)." From this, we can see that people in Taiwan were more accustomed to the flavor of black-bean soy sauce. Yellow soybeans are only mentioned once: "Yellow soybeans are round in shape and used for making tofu,” with no mention of soy sauce production. This suggests that yellow soybeans were reserved for making tofu.

Dry-fermented yimyu is known for its captivating, mellow aroma. But it presents a major concern for all yimyu makers: the raw sauce yield from dry fermentation is extremely low, and this has a direct impact on brewers' incomes. It's theorized, then, that wet fermentation arose out of economic necessity, modifying the process to incorporate brine.

Today, wet fermentation is the dominant method among Taiwanese yimyu producers, accounting for more than half of total production. It's worth mentioning that, among all the fermentation methods used in Taiwan, only dry and wet fermentation produce a unique byproduct known as jar-bottom yimyu. This occurs because the concentration of soybeans in the earthenware jars is so high that the mixture cannot be stirred during solar fermentation (this process is also known as static fermentation). As a result, the soy sauce separates into upper and lower layers, with the layer closest to the bottom possessing the purest aroma.

In 1895, Taiwan was ceded to Japan. Under the subsequent fifty years of Japanese governance, yimyu production was heavily influenced by Japanese soy sauce brewing techniques, leading to the development of the double-fermentation method. It is well established that this was modeled after Japan’s saishikomi shoyu ('twice-brewed soy sauce') technique.

As for water-based fermentation, this method was arrived at through two separate developmental routes, distinguished by the practice of rinsing the koji prior to fermentation. Koji-rinsing was an outgrowth of Taiwan's dry-fermentation method, differing only in that more brine was added – enough to allow the koji to be stirred, unlike in the dry process.

Meanwhile, methods that do not involve rinsing the koji more closely resemble the Japanese tamari shoyu production method, or that of Hui'an Soy Sauce made in Quanzhou City, in China's Fujian Province. However, after Japan launched the Pacific War in 1941, material shortages in Taiwan and the soaring cost of wheat led brewers to omit wheat and related ingredients altogether. This adaptation ultimately gave rise to what is now recognized as water-fermented yimyu – one of the most common forms of Taiwanese yimyu today.

Today, wet fermentation is the dominant method among Taiwanese yimyu producers, accounting for more than half of total production. It's worth mentioning that, among all the fermentation methods used in Taiwan, only dry and wet fermentation produce a unique byproduct known as jar-bottom yimyu. This occurs because the concentration of soybeans in the earthenware jars is so high that the mixture cannot be stirred during solar fermentation (this process is also known as static fermentation). As a result, the soy sauce separates into upper and lower layers, with the layer closest to the bottom possessing the purest aroma.

In Taiwan, the regions north of Taichung receive relatively little direct sunlight, and thus primarily adopt the water fermentation method. However, in Yilan and areas north of Hsinchu, frequent rainfall during winter and spring drastically shortens the period of time available for solar fermentation, which is essential for developing flavor.

To address this problem, yimyu producers in northern Taiwan’s rain-prone regions developed what is now known as the 'post-fermentation reduction' method. This approach compensates for limited sunlight by relying on extended post-fermentation heating and simmering to achieve a mature flavor. In doing so, it effectively resolves the problems of limited sun-exposure and insufficient fermentation, which results in a lack of flavor. This allows northern producers to maintain the quality and distinct character of Taiwanese yimyu.