Japanese Version

The Magical Mold of Sake by John Gauntner


The sake brewing process is still quite ethereal to most of us, being unlike any other brewing process we might be familiar with. It is not something most people have seen, and is a bit of a big “black box” for the majority of sake fans. That’s fine, really. No one says you need to know how something is made to enjoy it.

But should you have an interest, when you begin to read up on the topic, you soon hear about this mystery stuff called koji. The creation of sterling koji is indeed the heart of the sake brewing process. But just what is it, and why is it so important?


Koji is rice with a particular mold grown on to it, and works to break down starch molecules into sugar molecules which can then be processed by yeast cells, which is what fermentation is all about.


In winemaking, there is sugar already present in the juice of the grapes, and the yeast can then be added to that. For beer and other malt-based beverages, malted barley contains enzymes that are activated when soaked in hot water at very specific temperatures. These enzymes break down the starch in the barley into sugar to be used as food for the yeast. After this step, yeast is added, and fermentation begins.

masumi koji under scope eg

In sake brewing, there is no way to malt since the husks have been milled away, and only white rice remains. This means that enzymes cannot be extracted from the rice itself. Still, these enzymes must be supplied from somewhere, or the starch will remain starch, and there will be no sugar for the yeast to use as food, turning it into alcohol and carbon dioxide.

Enter the mighty mold Aspergillus Oryzae, the scientific name for koji spores. Although koji spores are found floating freely in the air, for sake brewing they are cultivated and sold by one of a half-dozen companies that specialize in that.

The dark greenish-yellow, extremely fine powder is sprinkled lightly over freshly steamed rice and coaxed into propagating on and into the rice grains. The process takes 42 to 50 hours or so, and is done in a special room, warmer and more humid than usual.

Chiyonosono “Kumamoto Shinriki,” known in the U.S. as “Sacred Power” Junmai Ginjo. Kumamoto Prefecture. It is made in Kumamoto, using Shinriki, a midsize rice that is easy to grow and harvest. From the late 1800”s to the early 1900s it was grown widely in Western Japan, and has not changed much since. It is the ancestor of much of today’s sake rice. Enjoy the rich, mellow flavor and deep recesses of this sake.


John Gauntner is one of the world’s most celebrated sake experts. He is an author, newspaper columnist and international lecturer. See John’s website at http://www.sake-world.com.

Author: stevebeimel

Share This Post On