How Rice, Yeast, Water, and Starter Shape Sake: A Lesson for the Intermediate Drinker

Two bottles can both read "junmai daiginjo" (a top-grade pure-rice sake milled to at least 50 percent) and still taste worlds apart. One is lush and aromatic; the other is as clean and light as water. That gap has nothing to do with the grade on the label. It comes from what the sake is made of and how it is made.

Four things do most of the work: the rice, the water, the yeast, and the starter culture. Pasteurization and aging then add their own finishing touches. This article is a step up for drinkers who already know the grade names: junmai, ginjo, daiginjo and the rest. If you want those terms sorted out, see The Difference Between Junmai, Ginjo, and Daiginjo; for the order of the brewing steps, see The Brewing Process. Here the question is different: why does a sake taste the way it does? Take these four factors one at a time, and you will be able to read the rice, yeast, and method off the back label and predict the flavor before the first sip.

The Big Picture: Four Factors That Decide Flavor

Start with the map. Each factor pulls on a different part of the taste.

From here we work down the table, one factor at a time.

Sake Rice: The Grain That Builds the Frame

Rice suited to brewing is called shuzo-koteki-mai (rice well suited to sake making), or sakamai (sake rice) for short. Good sake rice comes down to three conditions: large grains that resist cracking, a white starchy core at the center called shinpaku, and low protein.

The biggest difference from table rice is that shinpaku core. It looks cloudy and white because the starch there is packed loosely, leaving tiny gaps. Those gaps let the threads of the koji mold (koji, steamed rice cultivated with Aspergillus oryzae mold) work their way deep inside the grain. In making koji, brewers prize steamed rice that is firm on the outside and soft within, gaiko-nainan, "hard outside, soft inside." The shinpaku is what supplies that inner softness.

Low protein helps because rice protein breaks down into amino acids, and too many of them bring heaviness and rough, off notes. Daiginjo is milled to a rice polishing ratio of 50 percent or lower. The smaller the number, the more the grain has been polished away. The point is to strip off the protein-rich outer layers and leave only the pure starch near the core. That is exactly why you need a large grain that will not shatter as it is milled. Here are five representative varieties.

Yamada Nishiki forms its shinpaku reliably and resists cracking even under heavy milling. It is the most widely grown sake rice in the country and has long been the grain of choice for daiginjo. Dassai, from Asahi Shuzo in Yamaguchi, mills its junmai daiginjo "Migaki Nibu San Bu" down to a rice polishing ratio of 23 percent. That the grain survives milling this extreme is possible only because Yamada Nishiki is large and densely cored. Gohyakumangoku, with its bigger shinpaku, is said to be hard to mill much beyond 50 percent. Its resistance to dissolving translates into a clean, sharp finish.

Omachi is an old variety that stands behind both Yamada Nishiki and Gohyakumangoku. It is demanding to grow, and its acreage fell sharply for a time. Toshimori Shuzo in Akaiwa, Okayama (whose brand is "Sake Hitosuji") is known as the brewery that, together with local farmers, brought Omachi cultivation back. The grain dissolves readily into the moromi (the fermenting mash of steamed rice, koji, water, and yeast), giving a thick, umami-laden sake. Aiyama descends from that same Omachi and from Yamada Nishiki: its paternal line, Sanyu 67, is a cross of the two. It is difficult to grow, so only a few brewers work with it; Kenbishi Shuzo in Nada, Hyogo is known for using Hyogo-grown Aiyama alongside Yamada Nishiki. Its shinpaku is so large that the grain is fragile and ill-suited to heavy milling, but that same tendency to dissolve yields a rich, fruit-driven sake. At the very same polishing ratio, a different rice will change how long the finish lingers.

Water: What Sets the Pace of Fermentation

Sake is roughly 80 percent water. The water used in brewing is called shikomi-mizu (brewing water), and its hardness shapes the character of the fermentation. Hardness is a measure of the combined calcium and magnesium dissolved in the water.

To multiply, yeast needs potassium, phosphorus, and magnesium. Hard water tends to carry these, so it feeds the yeast well. Fermentation runs briskly, and the sake tends to come out powerful and sharp. Behind the reputation of Nada sake as otoko-zake ("men's sake," bold and firm) lies the water of Nishinomiya known as miyamizu. Kikumasamune Shuzo in Nada, near Kobe, is one of the breweries that brew with this miyamizu. Miyamizu is a moderately hard water of roughly 100 mg/L or more, which counts as hard by Japanese standards. Rich in phosphorus and potassium, it drives fermentation vigorously.

Soft water is low in minerals, and fermentation moves slowly. Because the moromi works gently, soft water suits a rounder, softer sake. This is why Fushimi sake is called onna-zake, "women's sake," gentle in style. Gekkeikan in Fushimi, Kyoto is among the breweries that brew with this soft Fushimi water.

Iron and manganese are the elements to keep out. Even a trace of iron darkens the color of the sake and damages its aroma. That miyamizu contains almost no iron is one reason it is prized as a famous water. Breweries obsess over their water source precisely because the elements they want and the elements they want gone fall into two sharply separate lists.

Yeast: The Player Behind Aroma and Acidity

Yeast decides most of the aroma. The "kyokai yeasts" distributed by the Brewing Society of Japan (Nihon Jozo Kyokai) are the standard strains used across many breweries. Most were isolated from the moromi of breweries that made outstanding sake, then distributed by number.

The ginjo aroma comes down mainly to two compounds. Ethyl caproate gives a sweet scent reminiscent of apple and pear. Isoamyl acetate gives a scent close to banana. Which one a yeast produces more of depends on the strain. Here are the well-known numbered strains.

No. 6 is the oldest kyokai yeast still in use, isolated in the early Showa era. No. 7 remains a staple that accounts for much of what is distributed today. No. 9 is known for its showy ginjo aroma and has long been favored for ginjo sake. No. 1801 was bred to raise aroma, producing high ethyl caproate while holding acidity down; it is often chosen for sake entered in judging competitions. When you want a highly aromatic sake, the yeast line on the label is a useful clue. The link between aroma and taste is taken up further in Taste and Aroma.

Building the Starter: Sokujo, Kimoto, and Yamahai

The starter culture, called shubo or moto, is what raises a large, healthy population of good yeast. To hold unwanted microbes in check, the brewer creates an acidic environment using lactic acid. How that lactic acid is supplied splits the method into three.

The sokujo starter was established by Edagawa Kamajiro of the National Brewing Experiment Station (today's National Research Institute of Brewing). He worked out that an acidic environment was needed to suppress stray microbes, and arrived at the method of adding lactic acid up front. Because it allows a short, safe fermentation, it is the mainstream today. Across the industry, sokujo accounts for roughly 90 percent of use, with yamahai and kimoto together making up only about 10 percent: that is how labor-intensive and rare these traditional methods are.

In the kimoto family, the lactic-acid bacteria produce compounds beyond lactic acid alone, so the flavor grows more complex. With that extra acidity, many of these sakes hold together well even when warmed. Daishichi Shuzo in Nihonmatsu, Fukushima is one producer that has made kimoto brewing the signature of the house. Yamahai is the kimoto method with the yamaoroshi step left out. Yamaoroshi is the backbreaking work of mashing the steamed rice and koji into a paste. The full name of the method, yamaoroshi-haishi-moto ("starter with yamaoroshi abolished"), is the source of the shortened name. Skipping the mashing means more contact with air, which can bring out a distinctive smoky note. For yamahai brewing, "Tengumai" from Shata Shuzo and Kikuhime, both in Hakusan, Ishikawa, are well known.

Pasteurization and Aging: How the Finish Changes the Face

What happens after pressing moves the flavor too. Hi-ire (pasteurization) is a heating step at 60 to 65°C. It suppresses the lactic-acid bacteria known as hiochi-kin, halts the work of any remaining enzymes, and stabilizes the flavor. Push the temperature too high and alcohol escapes; heat for too long and the aroma suffers, so it is done quickly.

Sake that skips pasteurization is namazake (unpasteurized sake). Because it ships with its enzymes still alive, it carries a fresh, youthful aroma. A sake that is at once muroka (unfiltered), nama (unpasteurized), and genshu (undiluted) is muroka nama genshu: neither watered down nor filtered, and correspondingly intense in flavor. Namazake changes quickly, so it is best kept cold and drunk soon.

How to Read a Tasting Note

Once you understand the factors, the vocabulary of taste starts to connect as cause and effect. This is where organic acids come in. Of the organic acids common in sake, three matter most to flavor: lactic acid, succinic acid, and malic acid. Most of the organic acid in sake is produced by yeast within the moromi; the rest comes from the starter and from the steamed rice and koji.

Acidity changes its face with temperature. In the drinking-temperature studies published on J-STAGE, lactic acid is reported to taste most sharply sour at 37°C and succinic acid at 50°C. Yet those same lactic and succinic acids feel soft and rounded around 37 to 43°C. Malic acid gives a brisk, refreshing taste at 10°C. In a blend of all three, acidity was clearly present and the flavors well balanced at 43°C. Here, in these numbers, is why some sakes make sense served warm.

In other words, the day you pick a kimoto junmai is a day worth trying it warm, because the umami of the lactic and succinic acids opens up with heat. Conversely, a showy ginjo built on No. 9 or No. 1801 yeast is at its best chilled, where the ethyl caproate aroma can rise. Changes with temperature are covered in detail in Temperature and Storage.

Read the rice, yeast, and method off the back label once, and you can see roughly where a sake's flavor is headed before you pour. The numbers are only a starting point. The real answer is in the glass you actually pour.

• This article is intended for readers of legal drinking age (20 in Japan). Please drink responsibly. Avoid alcohol during pregnancy or breastfeeding, and never drink and drive.