Although all that you will ever need to know about a sake is contained in one, intention-laden sip, sometimes the technical mumbo jumbo can be fun to study as well. The industry always seems to offer one more piece of information every few years, be it the amino acid level, the number of days the tank fermented, or something else. One such “something else” is kasu-buai.
Rice, rice milling and yeast are not the only things that make each sake different. Some tanks of sake are allowed to continue fermenting to (literally) the bitter end, so that every last drop can be pulled out of the fermenting rice mixture. While this will of course increase yields, it will naturally take its toll on quality. Many rough, superfluous flavors will result from this overfermenting.
Finer sake, however, is pressed earlier, so that not all the rice has completely fermented. This results in more refined, elegant flavor profiles.
After three or four weeks, the moromi (fermenting rice), koji (malt) and yeast is pressed to separate the clear sake from the lees, or unfermented rice solids. The white stuff left behind is the kasu. Naturally, the further the moromi has been allowed to ferment, the less remains at pressing time.
The kasu-buai, or “kasu rate,” is the ratio of the weight of leftover kasu to the weight of the original rice and is expressed as a percentage. So if you began with a ton of white rice and after pressing there is 200 kg of kasu left, the kasu-buai would be 200/1,000, or 20 percent.
The lower this number, the more the brewer attempted to get every last drop of alcohol out of the rice. The higher the number, the more they were willing to sacrifice potential yield for quality.
Most inexpensive, futsu-shu has a kasu-buai of about 20 percent. The next grade up, honjozo and junmai-shu to lower-grade ginjo-shu, have kasu-buai of about 30 to 40 percent. Fine daiginjo will often have a kasu-buai of 40 percent or even more. Naturally, these numbers will vary somewhat from product to product and from brewer to brewer.
For those with a further technical thirst, note this: Although a number of factors would need to be accepted as boundary conditions, there is a direct relationship between the kasu-buai and the number of liters of alcohol produced from, say, a ton of white rice.
For example, a typical kasu-buai for a honjozo sake might be 28 percent, yielding 380 liters of pure alcohol per ton of rice, whereas a typical kasu-buai for a daiginjo might be 50 percent, yielding only 300 liters of pure alcohol for the same ton of rice.
Note that how far fermentation has proceeded is not directly related to time. Daiginjo can ferment twice as long as regular sake, but the kasu-buai will be much higher.
To put it in a nutshell, for kasu-buai, higher is better. How high can it get? A lot of good daiginjo gets to 50 percent; the highest I have seen is the lavishly produced Sato no Homare from Ibaraki Prefecture, a shizuku (drip-pressed) sake with a 60 percent kasu-buai.
Only very good sake has this parameter listed on the bottle; and then only rarely. It is not something to get all worked up about. It is a little-discussed technical parameter even among sake-philes, and while interesting technically, its best use may be impressing your sake-drinking buddies.
On July 28, I will be holding a seminar on tasting and identifying various sake flavor profiles at the sake pub Mushu near Shin-Ochanomizu and Awajicho stations. (Note: No pottery; no Rob Yellin.) For details or to be put on a contact list for other sake-related events, e-mail email@example.com or fax (0467) 23-6895. You can also sign up for a free sake-related e-mail newsletter at www.sake-world.com
Masuizumi (Toyama Prefecture)
Masuizumi Ginjo is gentle up front, softly splashing on the palate at first, but soon firms up into a tightly bound sake with a discernible richness. A mildly sweet nose ties in nicely with this flavor.
The kura behind this sake is innovative, fun and creative. The brewers are not afraid to experiment and have created things like an all-koji sake and sake aged in a burgundy barrel. Their junmai daiginjo (a grade up), while not cheap, is a wonderful manifestation of the best of solid flavor and a well-defined fragrance.