A Guide to Sake Rice

Rice is usually the first thing most people think of when they hear the word “Sake”. Due to an unfortunate translation error, you might have been misled, but wine cannot be made from rice, so please refer to the overview page to clear that up. Sake is not a wine. But, Sake is made from rice.

However, just as grapes provide a character to the final wine, when it comes to brewing, the choice of rice can substantially impact the flavor of the finished product.

Rice is one of the oldest cultivated crops in the world ( domesticated 8000 years ago ) and as such, humans have found plenty of ways to improve upon varieties. These methods include: creating hybrids, selective cultivation, genetic engineering, etc.

New species are created to deal with the challenges involved with growing rice. Some are resistant to cold, while others resist various pests or extreme weather patterns. So, as nature changes, we will continue to adapt and find ways to grow food in those new conditions.

But, where did rice come from and how does it end up in a sake brewery? We’ll look at the genetic history of rice used for sake making and follow its journey to the mill, which the next page will extrapolate upon.

Where does rice come from?

All rice descends from wild grains in Southeast Asia. This phylogenetic tree indicates the timelines over which these strains diverged from one another. Domesticated rice descends from two species, Oryza sativa (Asian) and Oryza glaberrima (African), which have spread around the world into thousands of sub-species.

Oryza Sativa has several direct descendants, the most common are Oryza Sativa var. Japonica and Oryza Sativa var. Indica. By the way, “oryza” just means “rice” and…. don’t get too excited for this, “sativa” just means “cultivated”. In other words, “domesticated rice”.

The star of our industry is this mighty Japonica rice.

This name is “Japonica” is attributed to a Swedish botanist, Carl Peter Thunberg, who published, “Flora Japonica”, in 1784. It simply means “of Japan”. For instance, the Camellia Japonica, is just “The Japanese Camellia”. An alternate name is “Sinica”, which is based on the etymology for China (Sinæ->Sinai->Sin->Ch'in->Qin).

A basic comparison between these two varieties might be best summed up as: ”Japonica grains are short, roundish, spikelets are awnless to long-awned, grains do not shatter easily, and have 0-20% amylose content. Indica grains are long to short, slender, somewhat flat, and the spikelets are awnless. Indica grains shatter more easily and have 23-31% amylose content.” (source)

This short quote contains some critical words like “shatter" and “amylose”. There are many properties of rice that change per species and can have drastic effects on the fermentation process, not to mention the flavor, or durability. The shape of the rice can impact how easy or difficult is it to remove protein and fat from the grain, which in excess, can lead to off flavors. The stability, in terms of how well the grain resists cracking or "shattering, will determine many things from moisture absorption to consistency of enzyme content in the koji making.

How is Rice grown?

From seed to harvest, the process takes about 6 months, with timing varying by species.

• It takes about 5-20 days for the seed to germinate and a seedling to emerge.

• From a second leaf to about the 5th leaf, it takes another 15-25 days.

• Tillers (branches essentially) will emerge at each elongated node, generating the basic leaf structure of the plant. This process is another 24-42 days.

• At this stage panicles begin to form in just about 3-5 days. Panicles are a branched flower cluster. This will determine the potential yield of the plant.

• 19-25 days later, the rice plant will have visible flowers and will begin pollination as part of their reproduction cycle.

• Over the remaining 30-45 days, the seeds (rice grains) will develop, packing starch into them as a food source that will allow them to survive until they too can germinate and sprout their leaves. At harvest, the rice will have around 20% moisture content.

Of course, rice is harvested and does not continue its reproductive cycle toward sprouting, but this is not true for all rice. In fact, in order to continue producing farms full of rice, there are entire fields dedicated to creating seeds for other farms.

The key to the production of any crop it to know the final target volume of grains that need to be produced, because a decent amount of math is required to back track to how many seeds will need to be grown in order to ensure the final amount it reached. It can take many years to keep increasing the volume of base seeds before any actual product can be sold. Luckily there are ways to grow rice year round, but collaborating with farms in the northern and southern hemispheres to more quickly increase seed count, but it is still a 6 month turn around, either way.

What is the structure of Rice?

The structure of rice is mainly composed of: Proteins, Lipids (fats), and Starch. There are many different kinds of each of these that exist throughout biology, and learning which ones rice is composed of, as well as the percentages of each, can help us plan our fermentation. When growing koji, for instance, we might choose different spores or reduced the quantity of spores if the rice is polished less. We might soak and steam longer if it is a harder grain. We might expect the rice to be sticky if we are using a variety with less amylose than amylopectin and adjust our process accordingly.

The main components of rice that you should be aware of are the Hull, Caryopsis, Aleurone, Embryo, and Endosperm:

Hull (or Husk): Average hull weight is about 20% of the rough rice weight, ranging from 16% to 28%. The outer layer of the rice, known as the hull, shields the caryopsis. The hull's snug fit, which refers to the lemma and palea locking together seamlessly, has been linked to the grain's ability to resist insect infestation while stored. Additionally, the hull serves as a barrier against fungal infestation, as dehulled grains are more susceptible to colonization by Aspergillus spp. It is worth noting that Aspergillus does live on the rice plant as well as many strains of wild yeast.

Caryopsis (brown rice): The caryopsis, a single-seeded fruit, consists of a pericarp fused to the seed, which includes the seed coat, nucellus, endosperm, and embryo. Within the hull and enveloping the endosperm and embryo of the mature rice grain, there are three separate layers of compressed cells comprising the caryopsis coat: the pericarp, seed coat (tegmen), and nucellus.

Aleurone: The aleurone layer encases the rice grain and covers the outer surface of the embryo. It forms a strong attachment to the underlying cells of the starchy endosperm and extends over much of the embryo.

Embryo (germ): The embryo is situated on the ventral side at the base of the grain. The starchy endosperm surrounds the inner perimeter of the embryo. This is essentially the part of the rice grain that contains the means to replicate itself.

Endosperm: The endosperm consists of two layers: the subaleurone and the inner endosperm (central region). The subaleurone layer contains smaller starch granules but has a higher concentration of protein bodies and lipid bodies. In the starchy endosperm, cells with thin walls are typically elongated radially when viewed in cross-section. These cells are filled with compound starch granules and some protein bodies. The predominant contents of the cells are large, polygonal compound starch granules measuring 3-9 micrometers in diameter.

What is the composition of rice?

In addition to considering the structure of rice, it is extremely important to consider the “materials” that rice is composed of and how they are arranged. These will have direct and indirect effects on the fermentation.

Aspects that affect digestibility are the presence of a white core, protein body types, and sometimes mineral content.

Aspects that affect flavor and aroma are Starch, Protein, Minerals, Phenolic Compounds, and Lipids.

What is a White Core?

Some non-waxy (or non-glutinous) rice varieties exhibit “chalky” areas within the endosperm. When this chalky region extends from the center of the endosperm to the edge of the ventral side, it is referred to as a “white core”, “white heart” or (shinpaku 心白). An opaque section in the middle of the ventral (embryo) side is termed a white belly（腹白） or abdominal white, while a long white streak on the dorsal side is known as a white back (背白). Chalkiness in these regions has been attributed to the loose arrangement of starch granules.

In chalky regions of non-glutinous endosperm, starch granules are loosely arranged, somewhat spherical, and uncomplicated. In rice described as "crumbly," numerous granules exhibit rounded shapes on one or more sides. These softer areas contribute to a higher broken grain percentage during the milling process. High temperatures during ripening can result in a higher occurrence of grain chalkiness in japonica rice.

These grains with a prominent white core have a rough texture that readily absorbs water, making them ideal for preparing koji as Aspergillus spores (koji-kin) can easily penetrate the endosperm. Moreover, they dissolve and saccharify easily. Grains with a large white core are favored for sake brewing. However, the white core tissue contains numerous gaps and lacks structural integrity, making it prone to breakage during polishing. Since broken and intact grains have different weights and undergo different polishing processes, the rate of water absorption varies when they are mixed. This inconsistency adversely affects the rice's solubility and results in lower-quality koji.

How is Starch Structured?

In the context of “what makes good sake rice”, these are some key terms that relate to grain quality in terms of starch structure: “waxy”, “vitreous”, “mealy”, and “steely”.

• Waxiness is mostly a genetic trait that leads to very little amylose in the endosperm, meaning it is largely composed of amylopectin. This tends to make the rice easier to dissolve. Another name for this trait is “glutinous” and as you may already know, the term “gluten” and “glutinous” are completely unrelated other than describing texture. The soft and tender quality of rice that is glutinous/waxy is where that term arose from, but ALL RICE is gluten-free.

• Vitreous grains are glassy and translucent due to their dense internal structure. Non-vitreous kernels are soft, starchy, or may have chalky spots. Non-vitreous grains will also appear opaque. You may associate non-vitreous grains with the term “shinpaku”, however, it should be noted that grains with non-vitreous regions on the dorsal or ventral sides (white belly or white back), are far more prone to cracking during the polishing process and therefore less desirable.

• Steeliness refers to the hardness of the grain and it affects moisture absorption, starch retrogradations, gelatinization, and saccharification. It is due to many factors including hot weather toward the end of the growing season, low moisture content at the time of harvest, and other stress factors which change how densely packed the starch granules are within the endosperm.

• Mealiness is the opposite of steeliness and refers to a soft quality, and therefore is non-vitreous.

Based on genetics and greatly augmented by growing and harvest conditions, the aforementioned traits will be exaggerated. We’ll learn in the following pages how to account for these in the sake-making process. Let’s look at how meteorological aspects can affect the quality of rice.

As was mentioned before, Starch in rice is composed of either amylose or amylopectin. Amylose molecules are simply long chains of glucose molecules. Amylopectin molecules are large structures composed of many amylose molecules bound together in a branch-like manner.

The structure of these branches is largely determined by meteorological conditions during the “grain-filling” phase. Grain filling is quite literally when the flowers have been pollinated, and the seed is being physically constructed. When there are sustained high temperatures during the day and the environment does not cool down at night, it stresses the plant in such a way that creates long chains of amylopectin. One way to think of this is that the rice plant is not able to sleep. This might seem like a personification, but many plants and animals have a circadian rhythm during which they perform necessary procedures.

Long-chain amylopectin is difficult to digest because the saccharification enzymes are unable to physically access the glucose bonding sites. This will result in slow or reduced saccharification, leading to less sake yield and a higher sake kasu (lees) ratio.

A much more detailed look at the biosynthesis pathways behind amylose and amylopectin production shows us an extremely complicated, but fascinating view of the various steps that will determine the final starch composition of the endosperm.

There is nothing a brewer can do to effect this. However, the rice producers can have some impact on this. A quote from a research paper on the effects of Nitrogen application during the growing season reads:

”With moderate [Nitrogen] application, starch granule size increased… there were higher proportion of short branch-chain of amylopectin and lower proportion of long branch-chain of amylopectin with low relative crystallinity, ….gelatinization temperature, gelatinization enthalpy, retrogradation enthalpy, retrogradation percentage, hardness were decreased while viscosity were increased. At excessive nitrogen inputs, the grain quality was deteriorated and the opposite results of structure and physicochemical properties of rice starch were observed.”

(source)

Since nitrogen fertilizer can significantly affect the structure and physicochemical properties of rice starch, is something worth talking to your rice producers about and tweak things from year to year.

What are the effects of Protein Composition?

Coupled with the concepts presented above on the composition of rice and starch structure, protein types and composition also play a major role in the final product.

In brown rice, proteins make up 6-8% of the dry weight of the rice. In 70% polished sake rice, they still make up 4-6%. The protein content in rice is influenced by various factors including cultivation practices such as fertilizer usage, weather conditions, and the rice cultivar. Sake quality can suffer when produced from rice with high protein levels, often resulting in a harsh taste. Additionally, the aroma of such sakes tends to diminish during storage. Proteolytic enzymes in koji break down rice protein into oligopeptides and amino acids, which, when present in excessive amounts, can lead to adverse effects such as unwanted coloration and unpleasant taste.

As you see in the graphic from an article by Masaki Okuda, there are two fundamental types of “protein bodies" that we are concerned with. PB 1 is broken down into undigestible polypeptides and ends up as the sake kasu (dregs) after pressing. However, PB2 proteins are digested by koji protease enzymes and end up as peptides, amino acids, and oligo-peptide esters.

Furthermore, researchers have identified five types of bitter-tasting oligopeptides that impart a bitter and disagreeable taste to sake, although they can be eliminated through active-charcoal filtration. The presence of amino acids and oligopeptides in sake is greatly influenced by the glutelin content found in the polished rice grains.

We’ll go into this more in a future advanced article and break down each of these compounds from their precursors to their end products during the fermentation process.

What is Sake Rice?

In Japan, the Japonica rice varietals have been crossbred and selectively grown for so long that there are over a hundred sake rice varieties currently grown today. Click the link below to see a larger image of the breeding history of common varietals shown here (Chronology of Breeding Rice Suitable for Sake Brewing (Full size image)

Some strains, such as Omachi, are so old that we just know them as “wild strains” of Oryza Sativa var. Japonica, and from those strains many new varieties have been created.

The varieties in this graphic are categorized as “Sake Rice” (officially: 酒造好適米 - shuzokotekimai or just 酒米 - sakamai), a distinction that describes a number of qualities that are not typically found in the rice you’ll buy at the store, which is known as 飯米 ‘meshi-mai” or “eating rice”.

Perhaps a very important note to make here is that with the exception of “premium sake” such as ginjo, daiginjo, and competition sake, most sake is NOT made with sake rice. (source: John Gauntner) It is a good idea to keep this in mind when you are feeling that imposter syndrome and thinking “I can’t make good sake because I don’t have the good rice”. You can rest-assured that 65% of all sake in Japan is made with the same stuff you get in the store, though… we’ll talk in a bit about the differences in varietals and grain structure.

There are plenty of great sake that use “eating rice” and for the most part, choosing your rice is a business (ROI) type decision. Sake-rice is more expensive. Later we’ll describe some of the effects that it can have on yeast as well.

You can see a map here that shows common sake rice varieties and their prefecture of origin within Japan (Full Size Image).

Perhaps your area grows a type of rice that is unique. This is a great way to create a new flavors or market differentiation. In Europe, due to the climate, they have been experimenting with creating new strains that can grow locally for the purpose of sake brewing.

So, if sake is usually made without special rice, then it’s important to understand the distinction of WHY “sake rice” has been cultivated to possess certain qualities and how it benefits various styles of sake fermentation.

The main differentiators of sake rice are:

• Larger Grain Size, which means more starch.

• Less protein and fat (lipids), leading to lighter and cleaner sake.

• Concentrated starch center that forms a “Shinpaku”, making water absorption and steaming more consistent.

• Higher Shinpaku occurrence, leading to more evenly gelatinized rice.

• Price: 2-3x more than store bought rice.

• Good moisture retention:
  Doesn’t dry out as easily after absorbing water

The most common “sake rice” varieties are:

• Yamada Nishiki | 山田錦

• Gohyakumangoku | 五百万石

• Omachi | 雄町

• Hattan Nishiki | 八反錦

• Kame no O | 亀の尾

• Miyama Nishiki | 美山錦

Yamada Nishiki, known as the “king of sake rice”, is by far the most popular due to its consistency the following traits that lead to a reliable fermentation and end product:

Size and shape of the grain play a huge role in the potential of the sake it will produce because of the biological and chemical makeup of a rice grain. Lipids (fats), Proteins, and Starches are the key components that can greatly affect an ability to make quality Koji, provide sugars for the yeast, or could produce wanted (and unwanted) flavors and aromas.

Another key reason rice is chosen for sake making has to do with consistency of yield, ability to be polished without cracking, concentration of starch, consistency of moisture uptake, gelatinization, saccharification, grain texture, and many more qualities.

The weather during the growing process can also affect the rice properties and ultimately the sake quality . Experienced brewers have to account for these differences in the brewing process and it can take decades to truly possess the knowledge to know how.

How important is rice?

Considering it’s one of the core ingredients… it’s pretty important. But, let’s talk about why.

Resilience, Consistency, Sturdiness, Composition and Minerality… these are some of the tenants of rice quality and they have a direct impact on the sake production process.

Resilience

You can’t just think of rice as something that arrives in a bag. There’s a whole life that precedes that moment. From seed, to the field, the rains, wind, sun, and harvest. We must consider the all the factors that influence each grain.

Some rice varietals can only grow in certain regions of hot or cold weather. Some can resist pests and animals that prey on them. Some will fall victim to drought while others will survive typhoon winds and floods.

A species ability to survive contributes in a huge way to yield, which is just a fancy word for amount of seeds that survive through harvest. There are so many factors that can reduce yield, like lodging, which is when rice falls over because the stalk is too tall, weak, or the grains are too heavy.

We can only make sake if the rice paddy is bountiful, so there is inherently a correlation between the ability of a rice species to survive and the opportunity to transform it into sake.

Consistency

Survival may be the basic principal of production, but consistency give a species an ability to be relied upon, making it a malleable and controllable. Resilience plays a part in consistency, but additional traits make it even more sought after. Some strains grow to form a crystaline starch structure in the center of the grain that has a tiny air pocket. Light refracts differently because of this air pocket and makes it appear to have a “white heart” or “shinpaku”.

This particular structure increases the consistency of water absorption, steaming, and saccharification. When you can rely on these things, you can form a plan and spend less time correcting for errors.

Many aspects of sake brewing can become much more difficult if any of these are inconsistent. Koji grows too fast or too slow. Rice saccharifies too quickly or doesn’t melt enough.

Sturdiness

When rice is polished, if the structure of the grain is inconsistent it can break. For instance, if the shinpaku is formed off-center (white back) that will make it brittle. The structure of the grain is made up of proteins, lipids and starch. This start to relate to composition as well. Depending on how the grain is composed, it’s structure will either make it softer or harder. Softer grains also tend to crack.

Composition & Minerality

Also mentioned in relationship to sturdiness, the composition of the grain however, plays a huge role in saccharification and also the percentage of chemical compounds available to the koji and yeast. This will in-turn mean a change to aroma and flavor profile. Minerality is mentioned here because of the water and soil used to grow the rice. While a much larger topic, the actual nutrients used in the the rice paddy will ultimately end up in the rice and the fermentation. This is a one of the reasons that some producers have chosen to pay extra for organically grown rice. However, this is a very debatable topic since many non-organic rice producers are very conscious of this impact and pay close attention to sustainable farming.

Varieties

The variety of rice contributes an a huge way to the factors listed above. Choosing it is more complicated that simply reading descriptions. It takes a while to learn how each varietal behaves during the fermentation and after you start to know one variety well, the next year’s weather will undoubtedly change all the factors in ways that will make the rice harder or softer, the absorption faster or slower, and even the texture sticker or drier.

It is best to try different rice to develop a sense of how they are similar and how they are unique from each other.

After learning the flavor of rice and it’s many attributes, you must then consider the polishing rice.