I recently saw a section in “The Niigata Sake Book” labeled “How Much Sake Is Made out of 1 kg (2.2 lb.) of Rice” and thought this would make a nice topic to cover. I may later do a more in depth look at this but for now we will just get a good idea of the basics.
OK, so if we start with rice, water and some microorganisms how much sake will we get? Well, let’s start with brown rice as does “The Niigata Sake Book.” To make sake starting with brown rice the first thing that needs to be done is to polish the rice to a level needed for the type of sake we wish to make. To get down to the edge of junmai ginjo type sake we need to polish the rice to 60% or less. So let’s say we will mill the rice down to 60% of the original brown rice. That is, if we start with 1 lb. of brown rice this will leave us with 0.6 lbs. of white rice.
Now, for this there is a key ratio that needs to be understood. While this ratio will change somewhat for individual sakes, we will simply choose a reasonable example ratio for this analysis. The ratio of water used to the weight of rice added is around 1.3x, so that is what we will use. This implies the water needed for the fermenting mash will be 0.78 lbs. = 0.6 lbs x 1.3. The fermenting mash (the Moromi) will then be 1.38 lbs. = 0.6 lbs. rice + 0.78 lbs. water.
You may be thinking: what about koji? Well somewhere between 15 and 25% of the rice added is first used to make koji. It is this koji that supplies the needed enzymes to break down rice solids. The enzymes break carbohydrates into sugar and proteins into amino acids and peptides. So the koji is crucial in producing sake and determines how much of the rice remains as residue, lees or kasu once fermentation is complete.
The enzymes from koji will break down and liquefy all but about 30% of the original rice. In our case this amounts to 0.18 lbs. lees. Now, use a good press to separate the sake from the lees to get 100% separation. When we remove these lees from the Moromi we are left with 1.2 lbs. of sake = 1.38 lbs Moromi – 0.18 lbs lees. So, 1 lb. of rice can be used to produce 1.2 lbs of genshu sake. That is, full strength or cast strength sake; around 18 to 20% alcohol by volume.
Now we can convert this in to fluid ounces through the use of a few facts and a little math. A gallon of water weighs 8.35 lbs and is 128 fluid ounces. Alcohol weighs 0.785x water so a gallon of Alcohol weighs 6.55 lbs. Mixing volumes of 82% water and 18% alcohol gives a gallon that weighs 8.026 lbs. Given this, our 1.2 lbs of genshu sake has a volume of 0.149 gallons or 19.24 fluid ounces. So 1 lb. of rice produces about 19 ounces of genshu sake.
Most sake has water added to bring its alcohol level down to 16%. Sense we have 19 fluid ounces at 18% alcohol we have a total of 3.44 ounces of alcohol. To bring the percentage down to 16% we need a total of 21.5 ounces. Adding 1.5 ounces of water turns our genshu sake at 18% alcohol into standard sake at 16%. This means that 1 lb. of brown rice produces 21.5 fluid ounces of standard strength sake.
The analysis describe so far may be pretty close for commercial brewers but is overly optimistic for homebrewers. The missing element that needs to be included is the efficiency of pressing. The above assumes 100% efficient pressing. While somewhat optimistic for commercial brewers it yields completely unrealistic results for the homebrewer. To remedy this, we can include an efficiency factor by simply multiplying the result of the moromi minus the lees by an efficiency percentage. 100% yields the analysis result above. 65% brings the analysis results into agreement with homebrew practice.
OK, so what does this say about how much sake a homebrewer will get from a pound of brown rice? Well a typical batch of homebrew sake uses 10 lbs. of milled rice and 40 ounces of koji. But how much rice is needed to make 40 ounces of koji? That depends. For fresh koji, there is about 37 ounces of rice. However, for 40 ounces of dried koji 44.5 ounces of rice is needed. Anyway, depending on whether we assume fresh or dried koji will affect the results somewhat; between 3 to 4 percent.
Getting back to it, including koji, the typical homebrew sake uses roughly 12.5 lbs. of 60% milled rice which is 20.83 lbs of brown rice. From above, 20.83 lbs of brown rice and using our 65% pressing efficiency should produce 2 gallons of genshu sake or 2.3 gallons of standard 16% sake. This is 14 fluid ounces of standard sake per pound of brown rice. And there you have it.