Sake is made with four ingredients: rice, koji, yeast and water. All, except the koji, are familiar to most people. Koji is a mold culture grown on rice in the case of Sake. The mold is Aspergillus oryzae. It forms a white fluffy coating over the rice and excretes alpha-amylase which converts the rice starch into sugar. This is the primary function of koji in brewing sake; to provide enough alpha-amylase to convert most of the starch provided by the rice to sugar. Other compounds produced by the koji contribute to the final taste.
Once the koji converts the starches from the rice to sugar, yeast converts the sugars to alcohol. Beyond this major contribution the yeast also produces other compounds that contribute to the final taste and aroma of the sake. These two processes, conversion of starch to sugar and conversion of sugar to alcohol, proceed at the same time which allows the yeast to produce higher levels of alcohol than is the case in beer and wine. This is not to say that beers and wines can not ferment to the high levels that sake does but that special processes, outside the norm are needed to obtain the same high level normally reached with sake.
Short, fat grains of rice are preferable for making sake. These grains have a nice big ball of starch in the middle. The outer layers of a grain of rice contain a higher concentration of lipids, proteins, and fat than the inner parts of the grain. The lipids, proteins and fat produce undesirable flavors in the sake so the outer layers are removed in a milling process. Table rice (white rice) is produced by milling brown rice down to 90% of its original size. Various grades of sake are based on the milling level of the rice used:
- Futsu Shu is for rice milled to a level of 70% or higher
- Junmai means pure rice. Prior to Jan. 1, 2004, the rice also had to be milled to70% or more but this is no longer the case. (Specifically, pure rice signifies that no brewers alcohol or anything else is added)
- Ginjo is for rice milled between 50-60%
- Daiginjo is for rice milled 50% and below
Water is also extremely important to producing outstanding sake. The best water for making sake is a soft water that contains as little iron and manganese as possible. The softer the water the less crisp while harder water produces crisper sake.
Oh yeah, what about yeast nutrients, lactic acid and bentonite? Well the ingredients for sake as described above do not provide the needed nutrients for yeast to grow, multiply and perform well so we provide them.
Lactic acid is a naturally produced by the traditional method of brewing sake but most brewers have begun adding lactic acid rather than encouraging the growth of lactic acid producing bacteria, lactobacillus. This shift in process shortens the time needed and provides more control on the amount of acid in the sake. In addition, because the lactic acid producing bacteria is not encouraged in the beginning of the process their number is much lower so they are less likely to spoil the batch of sake.
Finally bentonite is used to help clarify the sake. It is really not needed. However, if you want very clear sake and are not willing to wait for it to clear, bentonite helps to bridge the gap.
So, how do these ingredients combine to make sake? Well, without going into too much detail let’s make a quick run through the process. The first thing that needs to be done is to produce or get the koji. For now let’s just start assuming we have koji. This is true for many home sake brewers so it is a good place to start. The next step in the process is to create the Moto or starter mash. This is the initial combining of ingredients. We start small because of the small amount of yeast we have to start and the yeasts inability to function properly in high concentrations of sugar. Starting with a small amount of koji and rice ensures that we don’t get too much sugar before the yeast has enough time to multiply enough to handle the amount of sugar. After the Moto, the Moromi begins. The Moromi is the main fermentation and includes three additions of koji, rice and water; each two times the size of the former. As with the Moto this gives the yeast time to multiply it population enough to handle the larger supply of sugar produced by the koji and rice. Finally, the Yodan step; this step involves a stabilizing addition of water, koji, and / or sugar. And voila, we have sake; age, pasteurize and bottle.