A question for sake brewers.
Background: I've made sake three times, and have also brewed about a hundred all-grain batches of beer. The first two times I made sake were several years ago. From memory, they turned out pretty well: I had a hard time separating the leftover solids from the finished sake, but the rice broke down pretty extensively. In one case I used special milled rice intended for sake, but it didn't seem to impact the process.
Each time I've used basically this recipe
In my recent batch of sake, I used distilled water, plain medium-grain rice, Wyeast liquid yeast, and my ususal koji-kin from Vision. I cooked the two portions of the rice separately, with each steamed for about an hour. The koji grew up normally. But during the yeast fermentation stage (two weeks at about 75 degrees F), the rice stayed mostly intact. I might have under-cooked it (I foolishly did not test the doneness by biting down on a cooked grain).
In the fermentation, how much does the rice really break down? I'm worried that if I over-cook it, bad things will happen. But it seems that at the fermentation stage, we want the rice to break down, so maybe it'd be OK to over-cook the larger second portion of rice, once the koji has grown up. Sound reasonable?