Moromi

(Main Mash / Primary Fermentation)

San-Dan-Shikomi (Three Additions)

With Koji and Moto being discussed already, the third most important aspect of sake brewing is “how it’s made”. The san-dan-shikomi is just that: one way of building a mash. But, even if brewers change ratios or add extra steps, the basic principles are the same.

The purpose of San-Dan-Shikomi is to continue building up your yeast population, which will prevent other microorganisms from contaminating the mash. On a home-brew scale ( less than 25L) this can be scaled back to about one or two additions because there are so many cells in a typical homebrew yeast pitch that it is more than enough to prevent contamination and if you adhere to good sanitary practices it should be okay BUT… be warned, this will have effects on the resulting flavor and potential ABV. [1]

Typically, each of the three additions helps to double the mash. If you did a traditional “moto” as described above, it would be about 5-7% of the total mash and you would add that into another 15-20% as part of the “soe” or “hatsuzoe” addition. This just means “first addition”. The term “hatsu-shikomi” means “first preparation” and usually refers to the whole process of preparing the rice, steaming, koji, water, etc. Just incase you see these terms used interchangeably in english, “shikomi” is “preparation” and “soe” means “addition”.

By combining the moto with an additional 15-20% of the total water, koji, and steamed rice, we begin to increase the yeast population. Typically one or two days are allocated for the yeast to increase the cell count. The day(s) of rest is referred to as “odori” or “dance”. If the yeast is ready for the intense fermentation ahead it should be quite active and bubbling. This might look different based on how well the rice you are using “melts”, but there will either be a smooth surface perforated by many “holes” or larger yeast bubbles collecting on the surface. If it is not, don’t be afraid to give it another day.

The second preparation will double the mash size again, adding about 25%. More water, koji, and steamed rice are portioned out and added. By now, the ferment should have melted or dissolved the structure of the rice enough that you can push through the surface and even crush the grains into a paste. Depending on your brew style, this may or may not be ideal. 

On the fourth day, the third addition is prepared, essentially doubling the existing mash again. This seems strange at first, given we have been numbering these days 1 through 4, but now that the mash is built, we call this “Day 1”. Counting the days of moromi helps to track the progress of fermentation and compare subsequent batches.

Various methods of tweaking the fermentation occur during all of these steps. For instance, the ratios of koji:rice:water, absorption ratios in the rice, how long the rice is steamed, and even target temperatures. There are some Toji that even practice 6+ additions over many days instead of just 3, or have several days of odori. The purpose of increasing the additions is to make the resulting sake sweeter and it also has the benefit of diluting the mash more slowly, so it prevents bacterial contaminations. However, it’s is a lot more work and takes a lot more time, so it’s not common.

We will dive into these topics and more in sub topics and try to provide examples and ways of working with them.

Temperatures

When you perform additions of water, koji, and rice in order to build up the mash volume, you’ll have to make decisions as to which temperatures to target for each addition. Typically, you’ll find these fall between 6C and 15C, starting higher to promote the melting of the rice during soe, which will lead to a healthier yeast culture during the odori day(s) and then dropping down to lower temps to prevent bacterial growth during the second and third additions. To prevent contamination the yeast must maintain a superiority at all times.

If you are a beer brewer, you are probably familiar with obsessing over temperatures to avoid off-flavors and aromas. Sake brewing is no different. Depending on the yeast strain, water chemistry, rice properties, koji, etc. you can expect various changes to occur if you don’t keep the temp below or above certain targets. For instance the 790 rule was developed in Hiroshima to address the soft water they were brewing with when they determined the koji, yeast starter and mash would all produce better results if temperatures were kept under certain values.

Managing the Moromi

Once you have built the mash (called Moromi in Japanese), you enter the primary fermentation. The focus of this becomes controlling the temperatures using various methods to cool and warm the mash, as well as adding water to both dilute sugar or dilute alcohol. Troubleshooting will be handled in separate documents because there are too many scenarios to include all in one section, so we will focus on the primary actions that relate to most ferments.

Typically for the tomezoe (final addition), the temperature is dropped to allow the yeast to have time to replicate while bacteria and other wild yeasts growth is inhibited. Temperatures then increase over the subsequent days as the yeast fermentation becomes invigorated. At first, the alcohol production will be slow, but as the temperature increases, so will the daily percentages of alcohol, acidity, and sugar as well.

Temperature has a direct impact on yeast performance as well as enzyme performance. However, this is where beer, mead, and wine makers will undoubtedly wonder, “what are the ideal temperatures?”. The answer to that will entirely depend on what kind of sake you want to make. Too high or too low and the enzymes and yeast will begin to produce high acid, reduce attenuation, or generate other off flavors due to yeast stress. 

Temperature will also have a direct impact on the length of your ferment. From 10 days to as long as 55 days. It will change the flavors, aromas, mouthfeel, and many other aspects. Wide swings in temperature will also have drastic effects. To control temperatures it is typical to either use some sort of glycol system or cold water to pump into an immersed radiator system or around the outside of the tank.

Another major piece of the main mash is osmotic pressure. Due to the unique nature of multiple parallel fermentation, both sugar and alcohol are being produced at the same time. Under certain circumstances, lots of sugar will cause the brix to skyrocket in the mash, overwhelming the yeast. This will cause yeast to express many different changes. In some cases, this can have a positive impact, forcing the production of such compounds as Isoamyl Acetate, with beautiful banana-like aromas lofting from the tank. In other situations, it can lead to a sharp increase in acidity, overwhelming the flavors and producing unappealing results.

The very nature of the choices and attention paid to your primary fermentation will have definite impacts on the final product, even as you decide when to press and filter. Tasting along the way will be critical to making these difficult choices.

At a production scale, you’ll use data from your first fermentations to help inform subsequent ones. Using A/B graphs and BMD Graphs, you can predict the trend of a known fermentation and adjust as necessary.

The main controls you have will be temperature and water. While some of this is for another document, it should be noted that if your yeast is outpacing your koji’s ability to produce sugar, you want to cool the ferment down. These can be small adjustments, but typically you’ll need several days for this to take effect. Even at 5°C, Kyokai 901 yeast can generate 0.5-1.5% ABV per day and will consume lots of sugar while it does. However the opposite problem might be observed: enzymes producing more sugar than the yeast can consume. If this goes unaddressed for too long, the yeast will experience a high level of osmotic stress and can either rupture their cell walls, or force them to generate high amounts of acid. By adding water, you will dilute the sugar, and the yeast will be invigorated. Typically adding 2% of totally water at a time, you can make slow, daily adjustments to course correct. (see A/B Graph)