In keeping with my discussion of Japanese foodstuffs (see fugu) this week, I thought I’d post a bit about the alcoholic drink sake. Sake, often called rice wine, has polished rice kernels as its raw material and is produced from the combined effects of a mold and a yeast. However the term “rice wine” is a misnomer since wine is fermented once while sake undergoes multiple fermentations.
Under normal conditions, the starch in rice is completely resistant to degradation by yeast enzymes—therefore it must be converted to sugar first. This feat is undertaken by the common mold Aspergillus oryzae, which easily breaks down the starch which remains after the hard exterior is polished off. During the process of making sake, this mold is cultivated beforehand in a very humid room on Koji rice (or malt rice). The moldy Koji rice, normal rice, and sake yeast mash (shubo) are then mixed together in a large vat. Here’s where it gets interesting.
Within the vat, a parallel process is occurring: as the mold breaks the rice starch down into simple sugars, these sugars are in turn reduced by the yeast to ethyl alcohol and carbon dioxide (to see the synthesis reaction, click here). This mixture is allowed to ferment for about a month, during which time more Koji rice, rice, or water may be added to achieve the desired flavor. At the end of this month, the rice mixture is placed in bags and then pressed to separate the alcoholic liquid from the solids. This liquid is left alone for another 10 or so days, when it is then filtered and pasteurized. The end product is about 18-25% alcohol. There are MANY different types of sake, with nearly infinite variations in the minutia of the brewing process, so the fermentation process I described is just the general picture.
Check out this flowchart on how sake is made:
Here’s another great source of information about the types and how-to’s of sake.