Taiwanese soy sauce begins with the black soybean. Compared to yellow soybean, its higher protein content produces deeper umami flavor when fermented. Yu Ding Xing also produces soy sauce in the Chinese and Japanese traditions using a blend of soybeans.

After the soybeans are pressure cooked, Yu Ding Xing inoculates them with koji culture. For Taiwanese-style soy sauce, they add toasted rice bran to assist the koji with fermentation, whereas for Chinese or Japanese-style soy sauce, they add wheat.

Following a few days of initial fermentation, the beans are rinsed, mixed with sea salt and water, then packed into a terracotta vat to ferment under the sun for at least six months. Many vats at Yu Ding Xing are decades-old.

The brew is extracted from the vat, pressed, then heated over a wood fire to stop the fermentation process. Although labor-intensive, slow-cooking the soy sauce over a fire enhances its flavor.