Part II　Shari: Sushi Rice

Chapter 8

Sushi Vinegar and Seasoning

The character of the shari (sushi rice) is decided by the sushi vinegar. Vinegar, salt, and sugar are not just ingredients for flavor. They also affect the moisture of the shari, how long it keeps, and even how quickly it hardens. In this chapter you will learn how vinegar is made and how to read its acidity. You will also learn the role of each of the three ingredients, and how to decide your restaurant's blend with clear reasons.

In this chapter you will learn

• To read the acidity of vinegar, and to recalculate the amount when you switch vinegars
• To explain the character of rice vinegar, grain vinegar, spirit vinegar, and akazu (red vinegar), and when to use each
• To explain the roles of vinegar, salt, and sugar in sushi vinegar, and how to think about the blend
• To explain the Maillard reaction, which creates the color and aroma of akazu, and how salt and sugar work through the number of particles they form (Grade 1)
• To explain the difference between coarse salt and roasted salt, and what each is best used for (Grade 1)

8.1　What is vinegar? Acetic fermentation and acidity

Vinegar is a seasoning made when bacteria called acetic acid bacteria turn the alcohol in an alcoholic drink into acetic acid. Acetic acid bacteria use oxygen to oxidize alcohol and make acetic acid. This change is called acetic fermentation.

For rice vinegar, you first make sake from rice. Koji mold turns the rice into sugar, and yeast turns that sugar into alcohol. When acetic acid bacteria are added to the resulting sake, it becomes vinegar. What the alcohol was made from, and how it was made, directly becomes the character of the vinegar.

The main component of vinegar is acetic acid. It also contains small amounts of other acids, amino acids, sugars, and aroma compounds. These small differences create differences in umami, richness, and aroma.

Reading acidity

A vinegar label shows its acidity. Acidity is the weight in grams of the acids in 100 mL of vinegar, counted as acetic acid. An acidity of 4.5% means there are 4.5 g of acid in 100 mL.

Vinegar sold in stores in Japan usually has an acidity of about 4.2 to 4.5%. For professional use, there are also high-acidity vinegars at 10 to 15%. If you use a high-acidity vinegar as is, the acid tightens the rice too much, and all you taste is a sharp, stinging sourness.

So whenever you switch vinegars, always check the acidity. Then recalculate so that the amount of acid stays the same. The idea is simple: multiply the current amount by the current acidity, then divide by the acidity of the new vinegar.

1. The current amount of acid　Suppose you use 200 mL of vinegar with 4.5% acidity. 200 times 4.5 is 900.
2. The amount of new vinegar　If the new vinegar has 5% acidity, 900 divided by 5 is 180.
3. The answer　180 mL of vinegar at 5% acidity contains the same amount of acid as the original 200 mL.

The strength of vinegar, and the acidity of shari

Vinegar is strongly acidic. How acidic something is, is shown by a number called pH. The lower the number, the more acidic it is. Shari mixed with sushi vinegar is roughly pH 4.0 to 4.5.

This acidity makes it harder for bacteria to grow. However, vinegar does not kill bacteria. It only makes it harder for them to grow. This is called a bacteriostatic effect, which inhibits growth but does not kill. As time passes, even vinegared rice is no longer safe (Chapters 6 and 9).

One more thing to remember is that acetic acid evaporates easily. When you heat it, it escapes with the steam. This property will come up again and again when preparing sushi vinegar and in shari-giri, mixing the vinegar into the rice (Chapter 9).

Vinegar standards, and making up the lost liquid when using vinegars from outside Japan

In Japan, the Japanese Agricultural Standards (JAS) for brewed vinegar set the names of vinegars and their minimum acidity. The minimum acidity is 4.2% for grain vinegar, 4.5% for fruit vinegar, and 4.0% for other brewed vinegars. Spirit vinegar falls into this category of "other brewed vinegars."

There are also rules on the amount of raw material. Grain vinegar and rice vinegar must use at least 40 g of grain or rice per 1 L of vinegar. Rice black vinegar, made from brown rice and similar grains, must use at least 180 g of rice per 1 L, and must turn brown or blackish brown through aging.

Vinegar itself has a pH of about 2.5 to 3.

If you switch to a higher-acidity vinegar and use less of it, the sushi vinegar also has that much less liquid. For example, if you cut 200 mL down to 180 mL, you are 20 mL short. If you make up this difference with hot water, the moisture in the shari stays the same.

8.2　Types of vinegar and their character

Sushi uses four main vinegars: rice vinegar, grain vinegar, spirit vinegar, and akazu (red vinegar). Rice vinegar is mellow and is the basis of white shari. Grain vinegar is light and clean. Spirit vinegar has little umami and a sharp sourness. Akazu is brown and has richness and umami.

Rice vinegar and grain vinegar

Rice vinegar is vinegar made mainly from rice. Amino acids and sugars from the rice remain in it, so its sourness is mellow, with a faint sweetness. Its aroma is gentle too. It does not get in the way of mild neta (toppings) such as white-fleshed fish and shellfish, so it is the most widely used vinegar.

Grain vinegar is vinegar made from several grains, such as rice, wheat, and corn. It is lighter than rice vinegar, slightly sharper in sourness, and clean. It is reasonably priced and steady in quality, so many restaurants use it as the base of their sushi vinegar.

Spirit vinegar

Spirit vinegar is vinegar made by acetic fermentation of distilled alcohol. It contains almost none of the components that come from grain, so it has little umami or richness, and its sourness is sharp and clean.

It has two main uses. One is to mix a little into rice vinegar or akazu to give the sourness more crispness. The other is to cure oily blue-backed fish such as mackerel and sardines. Its sharp sourness stands up to the oil, firming the flesh while holding down fishy odors (Chapter 16). If you make sushi vinegar with spirit vinegar alone, the sourness turns harsh and flat.

People sometimes say that spirit vinegar "kills bacteria better." However, the power of vinegar to hold back bacteria is decided mainly by its acidity. At the same acidity, spirit vinegar is not especially strong.

Akazu (kasuzu)

Akazu (red vinegar made from sake lees) is vinegar made from sake lees. It is also called kasuzu. The sake lees left after pressing sake are aged for 1 to 3 years, and sometimes for 5 years or more. They are then mixed with water and go through acetic fermentation.

During aging, the amino acids and sugars in the sake lees combine and turn brown. At the same time, a sweet aroma and umami develop. This is the same change that turns miso and soy sauce brown.

Akazu tastes mellow in its sourness and has richness. For this reason, Edomae (Edo-style) shari made with akazu is traditionally said to use no sugar. The akazu itself is already rounded, so it does not need sugar to round it off. Akazu shari takes on a pale brown color, and it goes especially well with strong-flavored toppings such as tuna, kohada (gizzard shad), and anago (conger eel).

The color and aroma of akazu: the Maillard reaction

The color and aroma of akazu come from the Maillard reaction. It is also called the amino-carbonyl reaction. In this reaction, amino acids and sugars combine to form brown pigments and many aroma compounds. These brown pigments are called melanoidins.

Sake lees are rich in amino acids and sugars. These react slowly at room temperature, over a span of years. The color of miso and soy sauce, and the browned crust of bread, come from the same reaction. The only difference is that bread takes a few minutes at high temperature, while akazu takes years at room temperature.

The acidity of akazu is around 4.5%, not very different from rice vinegar. It still tastes mellow because the amino acids and sugars from the sake lees wrap around the sourness.

Sake lees are what remains after the fermentation in sake brewing is finished. So making akazu does not need the step of turning rice into sugar, or the step of alcoholic fermentation. Rice vinegar goes from rice, to saccharification, to alcoholic fermentation, to acetic fermentation. Akazu goes from sake lees, to long aging, to mixing with water and acetic fermentation.

A closer look at spirit vinegar and black vinegar

Spirit vinegar is a type of brewed vinegar made by fermentation. It is different from synthetic vinegar, which is glacial acetic acid diluted with water. Its power against bacteria is decided mainly by the amount of acetic acid, that is, its acidity, and by its pH. So at the same acidity, it is not much different from other vinegars. However, if you choose a high-acidity product, its power against bacteria is stronger by that much.

A frequent topic in this certification exam is how to use grain vinegar and spirit vinegar differently. Spirit vinegar has little umami, but its sourness is sharp and pure. That sourness adds crispness and cures oily fish. This is all you need to remember.

Black vinegar (kurozu) is vinegar made from brown rice or barley, fermented and aged in earthenware jars for 1 to 3 years. During aging, the Maillard reaction turns it blackish brown. It is very high in amino acids, and its sourness is soft. It is rarely the main vinegar for sushi rice, but some restaurants add a little to akazu or rice vinegar for depth.

8.3　The three ingredients of sushi vinegar: vinegar, salt, and sugar

Sushi vinegar (awasezu) is a blend of vinegar, salt, and sugar, and it decides the flavor of the shari. None of the three is there for flavor alone. Each one also has a job beyond flavor.

Vinegar: sourness, and holding back bacteria

Vinegar brings out the sweetness of rice with its sourness and aroma. At the same time, it makes the shari acidic, which makes it harder for bacteria to grow. As we saw in 8.1, this does not kill bacteria. It is a bacteriostatic effect that only makes it harder for them to grow.

Too much vinegar makes the acid stand out, tightens the rice too hard, and spoils the flavor of the toppings.

Salt: the outline of the flavor

Salt gives the flavor of shari a clear outline. Shari without enough salt tastes sour yet flat and blurry.

Salt also has the power to draw out water. When you sprinkle salt on leafy greens, water comes out. This is the work of osmotic pressure. Inside a piece of nigiri, the salted shari draws a little of the extra moisture out of the topping. This is said to firm up the flavor of the topping. Some say salt also tightens the surface of the rice grains, but this has not been clearly confirmed for cooked rice.

Sugar: moistness and gloss

Sugar has the property of holding on to water. The sugar in sushi vinegar holds the water in the rice grains, keeps it from escaping, and stops the shari from drying out.

Sugar also slows the change that makes cooled rice hard. This change is called retrogradation (Chapters 7 and 9). In addition, sugar gives the surface of the grains a gloss and rounds off the sharp edge of the sourness.

However, too much sugar brings the sweetness of the shari to the front. It then covers up the delicate flavor of the toppings. Restaurants that use akazu do not use sugar because akazu already has the richness of sugars and amino acids. At restaurants that use white vinegar, the amount of sugar ends up deciding the restaurant's flavor.

How to think about the blend

There is no single right blend for sushi vinegar. 1 sho (about 1.8 L) of rice weighs about 1.5 kg, and it becomes about 3.3 kg once cooked. For this 1 sho of rice, use 180 to 220 mL of vinegar, 30 to 45 g of salt, and 0 to 120 g of sugar. Each restaurant decides its blend within these ranges.

Broadly, there are three styles. Edomae restaurants that use akazu use no sugar and season firmly with salt. Restaurants in the Kanto region that use white vinegar balance sourness and sweetness. Pressed sushi in the Kansai region uses more sugar to make the rice sweet and soft.

Much Kansai-style sushi is eaten some time after it is made. That is why it needed sugar's power to hold water and to slow hardening.

Decide the blend by how well it goes with your toppings. Restaurants with many rich, oily toppings make the acid and salt stand out. Restaurants that focus on white-fleshed fish and shellfish keep the acid gentle.

Record the blend in grams and milliliters, and weigh it on the same scale every time. Do not use tablespoons or cups. Even the same spoonful changes in weight with the size of the salt grains and the type of sugar. Tasting is only for the final fine-tuning.

Vinegar, salt, and sugar in more depth: thinking in numbers of particles

The difference between how salt and sugar work can be explained by the number of particles they form when dissolved in water.

Salt, that is, sodium chloride, splits in two when it dissolves in water. It becomes sodium ions and chloride ions. On top of that, a unit of salt is much smaller and lighter than a molecule of sugar. So at the same weight, dissolved salt forms more than 10 times as many particles as sugar.

Osmotic pressure is decided by this number of particles. Osmotic pressure is the force that pushes water to move from the weaker side to the stronger side when two liquids of different concentrations meet across a cell membrane. Salt, with its many particles, is far more powerful at creating osmotic pressure.

It is sometimes explained that when you add salted sushi vinegar to hot rice, extra moisture is drawn out of the surface of the grains. The surface then tightens, and stickiness is held down. However, the heat of cooking has already broken the cell membranes in cooked rice. The salt also moves into the grains. So a clear loss of water, like when you cure raw fish with salt, is unlikely to happen. This effect has not been fully confirmed.

What is certain is the effect on the neta. Inside a piece of nigiri, the salted shari draws a little of the extra moisture out of the topping, from the side that touches it. This is said to firm up the flavor of the topping and give it a clear outline.

Sugar, that is, sucrose, has many parts in its molecule that bond with water. That is why it holds on to water. In addition, sugar gets in between the cooked starch molecules. There, it gets in the way of the starch molecules sticking together again and setting hard. This is how sugar slows retrogradation. When a thin layer of sugar forms on the surface of the grains, it reflects light and creates a gloss.

Vinegar is also said to slightly change the proteins on the surface of the rice grains, tightening them and helping the grains stand up. It is also thought that the bacteriostatic effect of vinegar was one reason the nigiri sushi business could succeed in Edo, which had no refrigerators.

Changing the blend for the toppings and the season

Decide the blend to match your restaurant's toppings. Restaurants that focus on rich, oily fish such as tuna and buri (Japanese amberjack) make the acid and salt stand out to cut through the fat. Restaurants that focus on white-fleshed fish and shellfish keep the acid gentle. Restaurants that serve a lot of hikarimono (silver-skinned fish) hold back the acid in the shari, because the toppings themselves have already been cured in vinegar.

Restaurants also change the blend with the season. Many make the acid and salt a little stronger in summer, and hold them back a little in winter for a mellower taste.

They also change it for the rice. When the age of the rice changes, the way it absorbs vinegar changes. In autumn, when restaurants switch to new-crop rice, the rice absorbs vinegar less readily. So they either increase the vinegar by 10% or reduce the salt by 10%.

In markets outside Japan where people like "sweet shari," stop and think before adding more sugar. The sweetness guests ask for may actually be a lack of saltiness, or a sharp edge in the sourness.

8.4　Preparing and storing sushi vinegar

Prepare sushi vinegar in the following order. There is a reason for every step.

1. Weigh　Measure vinegar in milliliters, and salt and sugar in grams. Do not use tablespoons or cups.
2. Dissolve　Add the salt and sugar to the vinegar and dissolve them. If you heat it, use low heat and go no higher than about 50 to 60°C. Never let it boil. Acetic acid evaporates easily. If you boil it, the sourness and aroma escape, and even the volume goes down. Many restaurants use no heat at all, and leave the mixture overnight at room temperature to dissolve.
3. Rest　If you leave it for 1 day or more, the sharp edge of the sourness softens and the flavors blend.
4. Store　Keep it in a glass, enamel, or plastic container, away from direct sunlight, in a cool place. Write the preparation date on the container (Chapter 5).

Do not use aluminum, iron, or copper containers. The acid damages them, and metal dissolves into the vinegar.

Sushi vinegar has a low pH and contains salt, so it keeps at room temperature. However, once kombu or dashi has been added, it spoils more easily. Refrigerate it and use it up within 1 week.

Blending white and red vinegars, and preparing with kombu

Shari made only with akazu is dark in color and strong in umami, so it does not suit every topping. Shari made only with rice vinegar is light and suits mild toppings, but it is a little weak for tuna.

So many restaurants blend akazu and rice vinegar. The ratio of akazu to rice vinegar ranges from one to one up to about seven to three. When you change the ratio, the amount of acid also changes, so recalculate from the acidity. Some restaurants use two kinds of shari: a slightly sweeter white shari for white-fleshed fish, and a sugar-free akazu shari for tuna and hikarimono.

Some restaurants put a piece of kombu into the sushi vinegar and leave it for 1 to 2 days to transfer its umami. However, if you leave it in, it gives off sliminess and off-flavors. Take the kombu out within 2 days.

8.5　Types of salt and sugar

The main component of salt is sodium chloride. But depending on how it is made, the size of the crystals, the moisture it contains, and the amount of bittern (nigari) all differ. Bittern is found in large amounts in the liquid left after salt is taken from seawater. Its main component is magnesium chloride. These differences change how the salt works.

Coarse salt

Coarse salt is salt with large crystals, made by boiling down seawater. It contains moisture and bittern, and it is slightly damp.

Because the grains are large, it does not dissolve all at once when sprinkled on a surface. It is said to keep osmotic pressure working for a long time as it slowly dissolves. It does not make the surface suddenly salty, and it draws out extra moisture from inside over time. That is why chefs explain that it suits salt curing (shio-jime) of fish (Chapters 13 and 16). The magnesium in bittern adds a slight bitterness. It also helps firm up proteins.

Roasted salt and refined salt

Roasted salt is salt roasted at high temperature to drive off its moisture. Roasting changes the moisture-absorbing components of bittern into a form that absorbs little moisture. So roasted salt is dry, free-flowing, and fine-grained, and it dissolves quickly and evenly. It has little bitterness, and its saltiness is clean.

Refined salt is salt that is 99% or more sodium chloride, and its properties are close to those of roasted salt. It can be measured consistently.

Roasted salt or refined salt is best for dissolving into sushi vinegar, for sprinkling just before shaping nigiri, and for serving with toppings. They dissolve evenly and can be measured accurately. Seaweed salt and rock salt are salts for adding flavor, and they are not used as the basic salt in sushi vinegar (Chapter 20).

This certification exam asks about how coarse salt and roasted salt are used differently. Here is the answer. Coarse salt has large grains and contains moisture, and it is said to dissolve slowly and keep up osmotic pressure for a long time. So it draws out extra moisture from inside without making the surface suddenly salty. Roasted salt is dry and fine, and it dissolves quickly and evenly.

Types of sugar

Japanese soft white sugar (johakuto) has fine grains and dissolves easily. It contains invert sugar, so it gives a moist sweetness, and it is the sugar most often used in sushi vinegar. Granulated sugar is high in pure sucrose, with a clean sweetness and no off-flavors. Sanonto (light brown sugar) and kibi sugar (cane sugar) are less refined, and they have richness and color from caramel.

The type of sugar changes the quality of the sweetness. But all types work almost the same way in holding water and in slowing retrogradation.