Preparing the Rice
Rice must be cooked before it can be used for making sake. The reason, familiar to all-grain homebrewers, has to do with gelatinizing the starches in the rice kernels. Gelatinizing alters the structure of the starch granules in such a way as to make them more readily soluble, which in turn allows the enzymes provided by the koji to work their magic.
Bottom line: you have to cook the rice before you can turn it into sake.
The preferred method of preparing rice for sake is steaming. This is because steamed rice, while fully gelatinized, doesn’t have the tendency to go mushy and gooey like normally cooked rice does. This means that clumps are a lot easier to break up, and your hands will thank you for that when it comes time to mix the rice into the moromi. If you don’t have a steamer, can’t MacGyver one, and couldn’t find one to buy, then cooking in a rice cooker or even simmering in a pot on the stove will work – so don’t let not being able to steam your rice discourage you!
Don’t use boiled or simmered rice for making koji! Boiling or simmering rice forces a lot more water into the rice than steaming does, which seriously compromises the rice grain’s ability to hold any kind of structure. If you use this cooking method to prepare rice for making koji, the mold will reduce the rice to a slimy puddle of goo.
You prepare rice for steaming like this:
Wash the rice thoroughly in running cold water to remove all starch powder. The easiest way to do this is to just put the quantity of rice in a colander and rinse under cold water until the water running out of the bottom of the colander is no longer milky in appearance. Don’t obsess over this step, the water runoff will never be crystal clear; just rinse the rice for a couple minutes and move on.
Then place the rinsed rice in a bowl and fill with water to cover the rice in 2-3 inches of very cold water. Stash this in your fridge for about 12 hours (or on the counter for 2 to 3 hours). The goal here is to get the rice to soak up the water that will actually cook it during steaming, so use good water (RO water is fine). Properly soaked rice is slightly less than crunchy and nibbles easily (if it’s squishy, you soaked too long. if very crunchy, it hasn’t soaked long enough). This is also the appropriate time to add koji to the appropriate place for the step you are on (to some water in the same fridge for moto, or straight to the fermenter for moromi steps).
Soaking: How long you soak your rice for is really up to you. Temperature affects how quickly the rice absorbs water, and this is information the busy brewer can use to their advantage. You could soak the rice in the refrigerator for 12 to 18 hours and then drain and steam it after dinner the next day; or you can soak it for 1 to 2 hours on the counter in the morning and steam it in the afternoon. Either way, probably the best method of determining if your rice has absorbed enough water is to look for the rice to increase its volume by 33%.
After soaking, drain off the cold water in a colander for at least half an hour. It’s important for the outsides of the rice grains to be somewhat dry before steaming in order to help prevent excessive clumping and to allow steam to permeate the rice bed. Use this time to get your steamer heated up.
Place the rice in your steamer (with plenty of water in the bottom half) and steam for 45 minutes. Steamed rice is tender to the tooth and translucent – not white, like simmered rice. It also is not sticky if you rinsed it thoroughly, though it will have some tendency to stick to itself.
Now that you have an understanding of how to steam your rice, you are ready to move on to applying it to making your sake.