The Color of Koji: Like Everything in Brewing, Not Black & White

Greetings Sake Lovers, welcome to another KURAND Magazine article that introduces you to the world of sake.

The importance of koji is quite well documented, not only as an essential key ingredient in shochu but also in Japanese cuisine. It is less well documented though that there are in fact different varieties of koji, each with unique attributes.

One attribute, in particular, is color. In this article, we look at the different colors of koji available.

Starting with the Basics: What is koji?

Koji is steamed rice that has been inoculated with a mold of the same name. The fact that the finished product and mold share identical names often causes confusion, but in this article, we are referring to the finished product.

As a side note, in recent years, koji mold has attracted the attention of the health and beauty industry, because it produces a number of acids and vitamins that boost well-being (although not scientifically proven).

Rice is not the only ingredient that can be made into koji; any starch-based tubers and grains can be kojified, including wheat, soybeans (used to make miso). In Japanese, the little mold is called koji-kin. There are many ways you can translate this word kin: bacteria, fungus, etc, but mold has become the generally accepted one in the industry. The latin family name for the mold is Aspergillus. There are a number of members in this family.

The one commonly used in sake brewing called Aspergillus Oryzae has a number of relatives, namely, Aspergillus Kawachi used to make shochu, and Aspergillus Awamori used to make awamori and shochu.

In sake brewing, koji is, of course, an essential ingredient, because without available sugar in the rice, the starch has to be turned into sugar before any alcohol fermentation is possible.
The koji-kin produces the enzyme amylase that cuts up the chains of starch in the grains, thus effectively reformatting it into glucose. The process of turning starch into sugar is called saccharification.

Now, while there no western alcoholic beverages that use koji, there are plenty that relies on the same saccharification process—beer being the obvious example.

Koji has an effect on the flavor and aroma too. For example, sugar cane is the base ingredient for both kokutou-shochu (black sugar shochu) and rum, but the former tastes nothing like the latter and that’s because of the koji. Koji tends to give the end product a distinct umami (savory) flavor and unique depth.

The Color of Koji

But, now onto the main subject of this article, the color.

Each member in the koji family of mold is identified by the color of the final koji that it produces. As teased in the title of this article, the colors of koji include a black and white koji, but these are rarely used to make sake with notable exceptions. The black variant, kuro-koji (Aspergillus Awamori) is a legal requirement for awamori production, but can also be used to make shochu. The white variant is used for shiro-koji is mainly used for shochu. The variant used in sake brewing is, in fact, yellow, ki-koji.

These different variants are not just different in color; they also produce slightly different flavor profiles in the end product, this being the clue to the reason behind their different applications.
One reason why white and black koji never became the de facto sake koji is that they produce too much citric acid which doesn’t match the traditional flavor profile of sake, adding an undesirable tart aftertaste that while blends well with the high strength alcohol in shochu, destroys the harmony of the subtle lower alcoholic body of sake.

Even the white and black—while they both produce high levels of citric acid—are completely different beasts. So much so, that the shochu brand kirishima, produces both a black and white version of their signature product despite the process and other ingredients being identical. The one made with the black koji has a richer flavor than the white one which is more light and refreshing. The color of koji used is sometimes displayed on the label, though this is less common for sake than it is for shochu.

Let’s look at the different color koji in more detail.

Kuro-koji

The key attribute of kuro-koji is citric acid. It produces more citric acid than any other variety. Citric acid is important because it prevents other bacteria from breeding in the starter and main mash. Awamori is made in the warmer, more humid southern regions of Japan in temperatures that create a hotbed for unwanted bacteria growth, so this natural ability to sterilize the starter mash made kuro-koji a treasured advantage.

However, kuro-koji does come with its disadvantages. The main one is that it is hard to control the temperature and the spores contain a black colored pigment which can stain the brewing equipment and the brewery.
Kuro-koji is instantly identifiable from its powerful sharp aftertaste.

While originally, kuro-koji was rarely used in sake production, that is changing. Brewers have begun to exploit kuro-koji’s sterilization powers to help brew sake without the addition of lactic acid or the need to produce it naturally (if that point just raised a massive question mark in your head, see this article about making the starter).

The most famous sake made with kuro-koji would be fukumasamune. While the extra citric acid is noticeable, the brewery has found a way to integrate it without destroying the delicate harmony of the other flavors. Sake brewed with kuro-koji is thought to be effective in fatigue recovery.

Shiro-koji

Shiro-koji was born from the sudden mutation of kuro-koji. It is actually not white in color but is closer to a yellowish-green color. Just like kuro-koji, it generates a lot of citric acid, but unlike kuro-koji it does not create the same stain on the brewery. That is why, shiro-koji replaced kuro-koji—which used to rule the koji roost—as the koji for making shochu.

Side note: recently there has been a movement to return to the roots of making shochu and reevaluating the merits of kuro-koji. This has led to kuro-koji being widely used again.

There are plenty of similarities with kuro-koji, but shiro-koji tends to create a much more quaffable shochu with a very gentle aroma and still manages to retain the essence of shochu— authentic shochu but one which people don’t grow tired of.

As with kuro-koji, there are now sake made with shiro-koji as well; the most famous being denshu, ubudou, and jyouzen-mizuno-gotoshi. Shiro-koji tends to lend sake a less aggressive citric taste, something on par with a very citrusy white wine such as sauvignon blanc or chardonnay.

Side note: the citric acid is hardly noticeable in shochu because it has been distilled.

Ki-koji

This is one of the oldest koji. Its application includes miso, soy sauce, vinegar, and mirin. Producing much less citric acid than its relatives, it has to be stored at low temperatures. During the Meiji period, it was much more common than it is today to use ki-koji for shochu as well. However, ki-koji struggles in high temperatures and there was always a risk of moromi contamination, especially in the warmer climate of southern Kyushu. Research was carried out to find an alternative that could better withstand the climate. And then, in 1910, in the Ryukyu Islands, that research finally paid off with the discovery of kuro-koji and ki-koji was replaced as the mainstream koji choice.

Ki-koji creates sake with a fresh aroma like that of ginjo-ka. It could be said that this is the opposite of kuro-koji. Currently, production skills have improved, yet while still few in number, there is some shochu made with ki-koji. Shochu made from ki-koji has a fresh fruity flavor with much less body.


If you want to dive deeper into the world of sake, koji can make for a fascinating adventure. And speaking of adventures, there is no better adventure than tasting your way through 100 types of different sake, some made with different koji, at KURAND. We have branches all over Tokyo and for just one flat fee, you can taste as little or as much as you want, pairing with food, with no time limits. We look forward to welcoming you soon.