Factory Brewing
Commercial brewing of sake is similar to home brewing of sake, but on a much larger scale. The mass production of sake makes it possible to refine the ingredients economically on a scale that is unavailable to the home brewer. The process differs from brewery to brewery, but there are similarities that all breweries share.
Sake rice is milled down to a fraction of its original size. It is done in a way that does not generate an excess of heat which may affect the steaming of the rice, or friction which cracks the rice kernels, resulting in burst kernels once steamed. Depending on the quality of the sake, the resulting rice may be anywhere from 70% to 35% of its initial mass. The milling process removes oils and proteins, resulting in a higher concentration of starch.
Once milled, the rice is washed and soaked. The amount of milling dictates the proper moisture content for soaked rice, so there is a considerable amount of variance from one brewery to another. The soaking process allows for steaming of rice without rupturing the individual kernels, which adversely affects the fermentation process.
After milling, washing, and soaking, the rice is then steamed. Steam is introduced to the rice from below until the proper moisture content of the rice is obtained. Rice for sake is not cooked like rice at home. It is not submerged in water and heated until plump. The steaming process is very important to the characteristics of the finished sake.
Koji spores are allowed to colonize on rice in a warmed and humidified room or colonization container. The spores are inoculated in mass upon cooled rice and over the next few days the rice becomes coated with wispy strands of the fungus. Once finished, the rice appears to have fine gossamer coating. Once made, it is not stored for any period of time, since the koji breaks down the starch in the rice.
Water, special sake brewing yeast, steamed rice, and koji are combined to create a yeast culture. This culture is allowed to grow for two weeks, at which time a mash is created. Additional rice, koji, and water are added in stages over four days. It is carefully monitored for the next three to four weeks, and brewing conditions are adjusted to produce the desired flavor of the finished product.
Once the desired amount of fermentation is achieved, the liquid is then pressed from the solids. Modern commercial sake is commonly pressed by machine, allowing for the maximum amount of liquid separation from solid. Older methods, such as drip-separation, are still used today, though less common. Once the sake is pressed, it is filtered using charcoal to remove all solids, then it is pasteurized to destroy bacteria and to kill the enzymes responsible for the fermentation process.