Recently, I saw the term “awase-koji” on a bottle of sake. It was the first time I have seen that term, and it was on a bottle produced by a company whose president is very into unique marketing. So it may be in use by other brewers too; it may not. Regardless, it is neither official nor legally defined. Not that it needs to be either…
Awase means to put two things together that loosely complement each other, or in some circumstances to force them to work together. What it refers to in this sake-related instance is yellow koji (ki-koji), which is the standard type of koji used in making sake being blended with either white koji ( shiro koji) or black koji ( kuro-koji).
The various names are related to the final appearance of the koji and need no more explanation. More importantly, white and black koji are usually used in distilled beverages, shochu and awamori respectively, and contribute moderate to high levels of citric acid to the mix, something not found in any significant amount in yellow koji for sake.
This citric acid contributes sharpness and earthiness to the final product that is somewhere between rich and harsh, depending on your threshold for that kind of thing. So when it is used for sake – which is exceedingly rare, by the way – you can expect that sake to be earthier and decidedly sharp. It is not something that suits all styles of sake but can be delicious in the right measure.
It used to be anathema to use anything but yellow koji in sake brewing. Just the concept of black or white koji mold in the koji making room used to be unheard of, and sent shivers up and down the collective spine of the brewing staff. And, in truth, even today very few brewers do it. But those products that exist are very interesting and bold styles.
There are no rules or even tendencies among these sake in terms of black or white, or proportions of each mold used. And it is far from a trend. But such sake are out there and are worth trying should you come across one. And should the bottle say “awase koji,” you will know with what you are dealing.