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Making sake: the yeast starter (kōbo)


Kōbo (yeast starter) is an essential element in the process of making sake. Its role is to ferment the mixture, converting sugar to alcohol.


The ingredients of sake are rice, water, and kōji (the latter being a mold culture used to convert rice starch to fermentable sugars). When kōbo is introduced to these ingredients and cultivated, the result is called the shubo. It is also referred to as the moto.


The difference between kimoto and sokujō
To make good sake, a good-quality, pure kōbo (yeast starter) is necessary to produce fermentation. However, there are various kinds of bacteria and natural strains of yeast floating in the air that can have an adverse effect on the sake brew. If they get into the kōbo and propagate, the quality of the sake will suffer.


What prevents this from happening is lactic acid. The effect of lactic acid is to eliminate various bacteria and wild yeasts, so that the kōbo can propagate. In this way, shubo is produced.


There are two ways of producing lactic acid in the shubo: it can be developed naturally, or it can be added from an external source. The former method is known as the kimoto method, and the latter is called the sokujō method.


In the kimoto method, nature is allowed to take its course, and the brewer waits for the lactic acid to propagate itself. During this time, it is necessary to adjust the environment so that assorted bacteria and wild yeasts can not get a foothold, and this involves a considerable amount of labor. Using this method, it takes about 30 days for the shubo to be ready.


The sokujō method, on the other hand, is used by the majority of sake brewers. In this method, because lactic acid is added immediately, there is no concern that unwanted bacteria and yeasts might multiply.


With the sokujō method, it is possible to dispense with many procedures, and the shubo can be ready in around 15 days. Compared to the kimoto method, far less physical and mental effort is required.


Seeking out kimoto sake
In the kimoto method, the brewer has to rely upon lactic acid bacteria naturally present in the brewery to multiply, so the shubo is made in the cold of winter. There is a lot of hard, physical labor involved, and it takes place through the night in icy cold conditions.


While their number is small, there are some breweries that make sake according to the kimoto method. The question then arises: why do they go to the trouble of making sake by this more demanding method? The answer is that they can produce a robust sake that cannot be replicated using the sokujō method.


When a kōbo is cultivated, the culture has to win in a competition between naturally occurring lactic acid bacteria, other assorted bacteria, and natural yeasts. Because of this competitive environment, the kōbo culture that survives has to be a strong one. In this way, a kōbo is cultivated that produces alcohol of high purity.


There are, in fact, two different varieties of the kimoto method: the original kimoto method, and yamahai method that was developed from it. The kimoto method has been in existence since long ago, and the yamahai method was developed as a way of eliminating one procedure, known as yama-oroshi, from the kimoto method.


In the kimoto method, there is an operation in which the steamed rice and kōji mixture is pounded with wooden poles. This is known as yama-oroshi. The pounding is back-breaking work, carried out through the night.


The yamahai method was developed to eliminate the labor-intensive yama-oroshi procedure. Sake made using this method is yamahai sake. If the label on a bottle of sake says “yamahai shikomi,” it means that the sake is a robust, full-bodied drink made using a variant of the kimoto method.

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