Clarifying and Bottling
Right now you have a couple options:
After aging, you can leave the sake as-is (or mix the sediment into solution and rack to smaller bottles, followed by re-pasteurizing and sealing) and enjoy it as nigorizake (濁り酒) – cloudy sake that is meant to have the sediment mixed into the sake before drinking. This kind of sake is sweeter and has more body than filtered sake, and is always enjoyed chilled.
Pasteurizing sake is pretty easy. Just put your sake into a pot of cool water (start with cool or room temperature water to avoid shocking your glass!) on your stove, stick a thermometer in through the mouth of the bottle, and heat until the sake reaches 140ºF (60ºC). Then take it out, put a lid on it, and allow it to cool. The resulting pasteurized sake can be stored for up to 6 months before drinking (as nigorizake or muroka) or repackaging.
Or you can allow the jugs to become well-settled and carefully rack the cleared sake off of the sediment into smaller bottles, re-pasteurize, and seal. This is muroka ((無濾過) or “unfiltered” (more like “murky,” actually) sake – seishu that hasn’t been further clarified by filtration. It’s still pretty hazy, and that’s generally considered to be unacceptable for seishu. To render this sake brilliant, I suggest fining with bentonite – a type of clay used by vintners to clarify their white wines.
The ratio of bentonite used is generally 1/2 teaspoon per gallon being fined – for our recipe, that works out to 1.5 teaspoons bentonite. Start with a cup (8 fluid ounces) of really hot water. Stirring continuously with a whisk, slowly sprinkle the bentonite powder into the water. Once you have it all in a smooth slurry, gently stir it into your sake in its secondary fermenter (split it up if you’re using multiple jugs as secondaries). In about three days the bentonite will completely settle out and you can rack the brilliant sake off of the sediment for bottling and pasteurizing. There is, by the way, absolutely no reason why you can’t do this during the first pasteurization step in this process, followed by re-pasteurization during bottling. If you pasteurize your sake during this step, then the the temperature at which you store your maturing sake does not matter as long as you avoid extreme high temperatures. You can, however, speed the clarifying process along by storing the sake as cold as you can get it.
A product called Sparkolloid can also be used to clarify your sake. I don’t normally use it myself or recommend its use for sake, however, because it contains diatomaceous earth and can take a month or longer to settle out (and it never completely settles out). Most vintners that use it do so as a pre-filtration aid because of this.
I also frequently get asked about chitosan. Yes, you can use it, but I don’t think it’s quite as effective as bentonite for clearing the particular kind of haze that we’re trying to remove from sake. I tend to avoid it if only because I don’t want to take any chances with people who might have shellfish allergies (althouth chitosan is generally considered safe for those with that particular allergy).
Sake is ready to drink any time after it’s bottled, but a modest aging period of about two months mellow out some of the harshness that comes from using less refined sushi rice as the main ingredient. Traditionally, sake is aged at the brewery for six months in this stage of production, before filtering, bottling, and re-pasteurizing the product for sale. But I’m not going to suggest anything so extreme here, aging for 6 weeks to two months will be sufficient to tone down the “green sake” flavors.