Two-Stage Fermentations

Asian mold fermentations generally involve two distinct stages. In the first, dormant green spores of Aspergillus molds are mixed with cooked grains or soybeans, which are then kept warm, moist, and well aerated. The spores germinate and develop into a mass of thread-like hyphae, which produce digestive enzymes that break down the food for energy and building blocks. The second stage begins after about two days, when the enzymes are at their peak. The mixture of food and hyphae, called chhü in China and koji in Japan, is now immersed in a salt brine, often along with more cooked soybeans. In the oxygen-poor brine, the molds die, but their enzymes continue to work. At the same time, microbes that thrive in the absence of oxygen—salt-tolerant lactic acid bacteria and yeasts—grow in the brine, consume some of the building blocks, and contribute their own flavorful by-products to the mixture.