Sake koshu, also known as "Jukusei-shu" or "matured sake", refers to a specific category of Japanese sake that has been aged for at least three years. The term "koshu" itself translates as "old" in Japanese. This type of sake accounts for just 1% of total production, but unlike most sakes, which are generally drunk young to appreciate their fresh, fruity aromas, this one develops more complex flavors and characteristics specific to aging. Indeed, koshu are distinguished by their singular aromatic nuances, ranging from orange notes to caramel, almond and walnut. They offer a deep palette of flavors and a generally rich texture. The color also undergoes a transformation, adopting orange and amber hues.


Variations in color can be found in sakes ranging from the darkest (Nomirinko, 4 years old) to the lightest (Shuho +20, for example, a non-aged sake).


Today, we speak of "shinshu", to evoke a rather young sake, as opposed to "koshu". For the more fussy, sake deliberately aged for long periods is known as "choki jukusei-shu" (choki = long; jukusei = aged), but the term koshu will always do !

On this blog page, we'll try to answer any questions you may have about this category, and perhaps help you deepen your knowledge of sake and its history by encouraging you to taste it !



HOW DO YOU GET SAKE KOCHU ?
The process of aging sake can vary considerably. As a result, the different methods adopted by brewers lead to very different results. Sake can be aged in jars, vats, bottles or, much more rarely, barrels.

Some brewers use large vats at room temperature, resulting in sharper color changes and more pronounced flavors, while others prefer to age sake at lower temperatures, in chilled vats, preserving color, aromas and flavors to achieve a finer, more balanced profile.



Hybrid approaches also exist, combining aging in vats for a few years, sediment filtration, transfer to bottles, and extended aging at lower temperatures. The initial quality of the sake also plays a crucial role, since higher-quality sakes, such as Ginjo, often age more gracefully.



It is also possible to bottle-age sake yourself. Noticeable changes will occur after a year or so. However, this method is generally not recommended, as it's best to enjoy sake as the brewer intended, to savor all its originally intended characteristics.

AT THE ROOT OF SAKE'S TRANSFORMATIONS : THE MAILLARD REACTION
The Maillard reaction, also known as the glycation reaction, is a chemical interaction between amino acids and reducing sugars. It gives foods an amber hue and ripe aromas when subjected to heat or stored over an extended period. As sake ages, this reaction occurs between amino acids from rice proteins and residual sugars from the fermentation process, resulting in the production of melanoidin, a brown substance that contributes to the characteristic color and aroma of koshu sake.

At the same time, sotolon, an organic chemical compound present in aged sake, enriches the aromatic palette. It is frequently combined with aromas of nuts, honey, dried fruit, caramel, soy sauce, curry, fennel or even maple syrup. Certain types of rice, particularly those richer in amino acids, may contain sotolon precursors that evolve favorably during fermentation, contributing to the unique aromatic nuances of aged sake.

KOSHU IN THE HISTORY OF SAKE, A MATTER OF TAXES...
In the 13th century, sake was often aged, as members of the aristocracy adored this type of product, which was generally aged for three or five years. Aged sake was more expensive and considered precious, and most consumers preferred freshly brewed sake. It was during the wars with China and Russia that the government introduced a system of taxation on sake, a rich source of revenue.

When the tax laws of the Meiji era (late 1800s) were in force, sake taxes accounted for over 30% of all taxes collected by the state. So, to ensure that the money was received as quickly as possible, taxes were due at the time of pressing, i.e. at the end of the brewing process, before the sake was even marketed. Naturally, no kura wanted to wait three to five years to get their money back, and risk the sake going bad. This law finally changed some fifty years ago, and brewers are now taxed when the sake leaves the kura. It is this change that has enabled new experiments in aging.

THE BREWING YEAR DATING SYSTEM
Very often, the label specifies a "3-year koshu" or a "5-year koshu", for example. The term "jukusei" meaning "aged" or "refined" is sometimes used instead. Of course, this information is only useful if we know that the sake has only recently come out of the kura, because if it has been sitting on its own shelf for some time, then we'll need to take that time into account. But sometimes, we simply see an indication of the brewing year. This should simplify things, provided you know how to read this information.

The problem is twofold : on the one hand, Japan doesn't use the same dating system as the West, but a year-numbering system based on the reign of the current emperor, and on the other, a given sake-brewing season spans two calendar years.

First of all, although Japan refers to the fact that it's 2024, officially and traditionally it's called Reiwa 6, i.e. the 6th year of the Reiwa era. If a bottle is labelled as having been brewed in year 2, this means that it was brewed four years ago, in 2020.

Sake brewing then begins in the autumn of one year and ends in the spring of the next. So, if a sake were labelled only as Year 15, we wouldn't know whether it was the season from Autumn 14 to Spring 15, or Autumn 15 to Spring 16. These are two different years in terms of brewing, so we need a little more detail. This point was not lost on the tax department, which was looking for a more efficient way to tax kura on their production. So, long ago, they created the concept of the "brewing year" or "BY" (for "Brewing Year"). Just as fiscal years can differ from calendar years, in Japan the brewing year runs from July 1 to June 30 of the following year. It thus encompasses the entire brewing season in a 12-month period. Thus, the BY5 year runs from July 1, 2023 to June 30, 2024. Sake brewed last autumn and spring of this year would therefore be considered part of the BY5 year.

From now on, when you see this nomenclature, you'll know exactly how old your sake is.