Sake Brewing Process

A Complete Sake Fermentation Overview and Guide

The first thing you should learn about sake brewing is that is it very difficult. Experts in beer, distilling, wine, and other forms of fermentation all agree that is it not just difficult, it is the most difficult form of fermentation because of a term called Multiple Parallel Fermentation.

Put simply, all forms of alcoholic fermentation you need a lot of sugar and then yeast breaks that down into alcohol.

• For wine, that sugar is already present in grapes.

• For beer, you germinate malt to convert starch into sugar, and then you ferment a fixed amount of sugar into alcohol.

• For sake… we have active enzymes that come from a second organism called Aspergillus Oryzae, which play a parallel role in breaking down starch from rice into sugar at the same time that yeast is converting it into alcohol. Basically, you don’t have an “original gravity”, so all the calculations for alcohol and attenuation are useless.

In addition to the pure conceptual way sake it different, there are additional elements that make sake “multiple” parallel fermentation. Sake is made in open top fermenters and usually involves several tank transfers in the open air. As we will discuss later on, one quarter of the raw materials is made into “koji” which is steamed rice with Aspergillus grown on top of it, and the growing conditions make it susceptible to all kinds of bacteria.

The trick to making clean, refined tasting sake is all in the details of “what is important” and “what is NOT important”.

Let’s start by understanding the full process of how sake is made and then we’ll dive into the details in the next sections. Checkout our advanced section for more nuanced topics.

Let’s answer some basics first:

Is sake really rice wine? (no.)

Sake is a “brewed” beverage, fermented from the starch of rice, that is hydrolyzed by steeping in water, then steamed to gelatinize the amylose and amylopectin so that enzymes can break down those molecules into glucose, which can be consumed by yeast.

As we said earlier… It is also not to be confused with wine making, which requires that you ferment fruit. To make wine you crush grapes and add yeast. There is no starch involved. In fact, you might know the term “Fructose”, which is like a cousin of “Glucose”. The latin term “fructus” means “fruit”. The presence of these sugars makes it simpler to get from raw material to finished alcohol, but we’re not here to oversimplify the art of wine making, just point out the difference in where sugars come from.

Beer by contrast, is made with Barley and other grains that contain starch. This starch must be converted to sugar before the yeast can turn it into alcohol. The way we do this is through a process of introducing water and heat to the rice. Otherwise known as “Brewing”.

Sake is made with rice, which contains “starch”. So, just like beer … sake is a brewed beverage.

By the definition “to make or prepare (a beverage, as tea) by mixing, steeping, soaking, or boiling a solid in water”, rice is first steeped in water and then steamed (heat) to gelatinize the starch inside the grain.

We’ve chosen to add a quick note on “distilling”, because sake is often bundled into this category, but it’s incorrect. Sake is not distilled. Distillation is the process of heating an existing alcoholic beverage to evaporate the alcohol from solution and condense that vapor into a concentrated form. So once again, sake is NOT distilled. Those products are typically 40-60% alcohol and are often sold as 80 or 120 proof.

If you are asking yourself… “what is it that the Japanese make that has rice and is distilled?”… well, you’d be referred to Shochu, the sort of Japanese version of Korean Soju. Shochu is a distilled beverage that CAN be made with rice and in fact, it can also be made with finished sake or even from the ‘dregs’, known as Sake Kasu, which you can re-ferment and then distill. This is a great topic for another website: DistillShochu.com. Godspeed.

So let’s dive in a little more and describe the most common way to make sake from start to finish.

Sake Making Process Overview

Here is a birds eye view of the sake brewing process:

1. Grow Rice: Sake Rice takes 6-8 months from seed to harvest.

2. Process Raw Rice: Harvested rice is dried from 25% moisture down to about 12-15%. The husk is removed by a machine. At this point it is brown rice.

3. Polish Rice: A special vertical milling machine carefully polishes the brown layer off the rice until it reaches the specified percentage. 0-93% of remaining rice. The more you polish, the less protein and fats remain.

4. Stabilize Rice Moisture
   The polished rice loses moisture from the heat of the milling machine and usually requires 2-3 weeks to stabilize around 12-13%. For the next step, this is usually referred to as “Dry Rice” and for the purposes of water steeping, call this 0% moisture, unless in specific circumstances.

5. Calculate a Recipe
   Dry rice weight is used to calculate a brewing recipe. Typically tank size (liters) is multiplied by 0.3 to determine how many kilograms of dry rice are needed. Portions of this rice quantity will be allocated to “steamed rice” or “koji rice”. Some recipes will even use different types of rice or polishing rates.

6. Wash the Rice
   Rice needs to be washed to remove all the bran that is stuck on the grains from the milling process. There is a range of methods to achieve this, but for some styles, careful attention must be paid to water temperature and other aspects of handling the rice to prevent cracks that affect moisture rates.

7. Soak the Rice
   Rice needs to be soaked in water so that the hydrolysis reaction of gelatinizing starch can occur during steaming. Each strain of rice and polishing rate will absorb water at different rates. This process can last from seconds to hours. It requires testing to determine. Typically the dry rice gains about 28-33% of water weight. After soaking is complete, time is allocated to allow the water to diffuse fully into the grains.

8. Steam the Rice
   This is actually the “brewing” part of sake brewing. The presence of water, diffused into the rice grains, disturbs the starch, causing fractures in the crystalline structure that allow steam to enter. It’s important to recognize the distinction between a “rice cooker” and “rice steamer”. The intention in this step is to simply apply heat in order to gelatinize to the starch, but depending on the temperature and saturation of the steam it will gain an additional 4-10% of water weight, totaling 32-40%. Though, homebrewers might experience as high as 45-50% total absoption.

9. Cool the Rice
   The rice exits the steamer at 100°C. Skipping over many decisions regarding the handling of koji rice, some of the steamed rice is allocated to the koji room and other rice will go straight into a tank. The temperature the rice is cooled to depends on recipe configuration.

10. Make Koji
    This is a 40-60 hour process that cannot be overstated. We’ll break this out into a separate page to address it in great detail, but suffice it to say, this is often considered the most important part of sake making. A metaphor applied to the effects koji on the fermentation process is that of a steering wheel. Depending on humidity levels, spore ratio, inoculation temp, room temp, and oxygen levels, koji will grow at various rates and produce different enzymes that are deposited in the grain. The enzymes in koji are how starch becomes various mono and poly saccharides, proteins are converted into peptides and amino acids, and lipids become fatty acids. The resulting profile will strongly influence the flavor and aroma of the final sake. Due to non-sterilized environment in which koji is made, it is also the major source of contaminating bacteria in a sake fermentation, which may or may not be desired depending on the step.

11. Yeast Starter (Shubo/Moto)
    The yeast starter is considered the next most important element to sake brewing. If the koji is the steering wheel, then the Yeast starter is the driver. Unlike beer and wine where quantity of yeast becomes a major point of discussion, in sake brewing, yeast is conditioned through various stress inducing practices to prepare them for the long fermentation that lies ahead.
    
    A yeast started is made with about 4-8% of the total raw materials (water, koji, rice, and yeast). There are big choices to be made at this stage to determine the kind of yeast starter, which can last from as little as hours to over a month. The shortest option is basically a pure pitch of large quantities of yeast, but you could consider the yeast medium a basic starter.
    
    The success of any yeast starter depends on the pH of the liquid which can be manually adjusted with lab grown lactic acid or naturally developed in a similar process to lambic beers as waves of different bacteria slowly develop the level of acid needed to kill off other bacteria, including themselves. More on this later…

12. Main Fermentation (Mash/Moromi)
    After the yeast starter is complete, we’ll add it into a larger tank and then begin to double the fermentation by adding more koji, rice, and water. Typically this is done over 3 different days, with one day tossed in the middle to help ensure the yeast never lose dominance over bacteria in the mash. You may be familiar with this process known as san-dan-shikomi or (three step addition)
    
    On the final day, when all the ingredients have been added, we begin counting this as fermentation day one.
    
    Over the next 10-35 days, depending on the recipe, you allow the temperature to rise or control it through varoius cooling techniques. In some cases, warming procedures might actually take place, but that is very rare. The yeast will generate lots of heat on their own.
    
    An important detail to remember is that the koji continue to replace sugar in the mash as the yeast ferments it into alcohol. So while the specific gravity might start at 1.050, it’s possible that the effective gravity totalled to 1.18 because the gradual attenuation can result in 22% alcohol.
    
    Some styles actually add alcohol during the three step addition, or on the final day of fermentation. These can increase aroma or give a fortified texture to the final product.

13. Pressing
    When the yeast has begun to slow down and the specific gravity falls closer to or below 1.000, the fermentation needs to be cooled down to 5°C or below for 1-2 days so the yeast can clean up their environment and then we place all the liquids and solids into a press of some kind, apply pressure, and capture the sake that comes out of the cloth.
    
    There are several methods for pressing sake kasu into filtered sake, but as with other aspects of of sake making, the choices you make will have drastic differences in the final product.
    
    Some of the kasu (dregs) are sometimes captured at this point in the process to be used for making nigori (cloudy) sake.

14. Finishing
    A number of steps here are being grouped into a single bullet point because there is so much variation in process that its difficult to say when or how each should take place, but here is an unordered list to list elements of fine-tuning sake to meet the requirements of your recipe:

    • settling (allowing solids to fall out of solution)

    • charcoal / membrane filtration (removing fine particles, enzymes, yeast, and even discoloration)

    • pasteurization (ex: snake tube, plate, tunnel, in-bottle) to reduce the change of spoilage

    • maturation (storage at pre-determined temperatures that will effect the final flavor)

    • oxidation (usually bad, but can have some positive effects)

    • blending (many tanks made into one large tank helping with consistency in the market)

    • flavoring (while not common in Japan, sake is blended with other fruit/vegetables to create new products)

    • aging (some sake is intentionally aged to develop unique flavor profiles)

    • sparkling (secondary fermentation in bottle or forced CO2 in pressurized tanks)

15. Packaging
    Bottles, Cans, Growlers, Kegs… you can do it all. There are endless ways to package your sake, but keep in mind that some sake must always remains cold (namazake) or the flavor will change quickly. If UV light can get through the container is can “skunk” the sake and give it a “sunlight” smell. Other discolorations can occur as well from light exposure.

16. Cleaning
    Oh… we almost forgot…50-80% of all work in sake brewing is cleaning. It doesn’t mean you have to use chemicals, it just means that surfaces need to be washed… and thoroughly. Removing “food” for bacteria, allowing tools to dry… these are all ways to mitigate contaminations, but these are all important.
    
    We’ll go into this in much greater detail and many other topics, so keep reading!