I've tried several large batches (10 lbs of rice) with sweet and jasmine rice and they have been coming out with a sour taste. The general consensus was that by adding too much water, it somehow made a sour batch, but some Chinese friends of mine have always added 1.3 x water to the weight of the rice. (13-14 lbs water) They told me that they don't even make it in the summer time and that @ 60 degrees is best temps for it or it gets sour. So my thinking was that temps had more to do with getting a sour batch than the water. They also said to not be afraid to stir it every day. That's a problem I've had in the past.. having a big plug of rice on top not getting converted.
So... I made a batch up last month that should be done in a few days (Jan 14) and have left the batch in a room that stays colder in the house with the door shut. I used 10 lbs sweet rice cooked at 5 cups water to 3 cups dry rice, 1 bag RYR ground up with 10 yeast balls. After the rice was done, I added 1.5 gals cold water, stirred it up, which brought the temps down enough to add the yeast balls/ryr mixture. Stirred well and put back in the cold room. I popped the lid on it and stirred with a sterilized spoon every day for the first week and a half. It needed it. Every day, there was a thick dry-ish layer of rice on top.
After the week and a half, the dry-ish rice had been converted enough that even though it was still floating on the top, it was in liquid, so it wasn't going to make a plug of starch any more. A couple days ago, I decided to give it a taste to see how it was doing. Rice wine without any added water is way too sweet for my taste. The reason it's sweet is there's still a lot of residual sugar from the converted starch for the yeast to eat, but the yeast has reached it's alc. tolerance level and stalled out. The added water dilutes it to where it lowers the alc. level and more of the sugars can be eaten by the yeast. You just have to find that combination that's correct. Too much water and you get a watery wine. Too little water, and you get a sweet wine and wasted the potential to get more.
ANYWAY... I tasted the wine and thought "Wow!" This is hands down the best batch I've made. My wife hasn't liked any of the other batches, but I let her try this one and she even likes this one. My son's girlfriend has tried most of my batches and I let her try some and she said, "Wow! This is the best one you've made!" It's still a sweet taste, but not sickeningly so. Just a medium sweet with a really nice warmth after you drink it.
As I said, it should ne ready in a few days, but I guess the colder ferment temps have slowed things down and there's still a few CO2 bubbles coming to the surface. May give it an extra week, but I'm stoked about this batch. The level of the ferment bucket looks to have 4 1/2-5 gals in it, but after straining, I should be left with at LEAST 3 gals of goodness.
I guess I need to get another batch going while it's still winter! lol. I'll post some pics when I go to bottle it.