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The Science of Sushi: What is Sushi and How to Make It

The Science of Sushi: What is Sushi and How to Make It

What is sushi and how to make it the best way possible? Helped by science and physics, we provide you a guide to become the ultimate sushi masters at home.

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Rice and fish: have you ever thought what is sushi and how simple it is? Of course, if it was so easy, this age-old tradition would be inexplicable: sushi is more than just a dish, it is a veritable gastronomic philosophy of Japanese food. You may not yet be a true sushi master, but here are a few pointers that, with the help of science, will enable you to prepare perfect sushi, even if it's your first attempt.

Let's start with the most often-abused ingredient: rice. The Japanese tradition involves ancient and highly poetic rituals, necessary in order to cook it properly. But today, we will approach it as laymen, and take a more scientific approach to these small grains. When it is first harvested, rice is protected by a husk, which is then removed. At this point, the grain comprises three parts: bran, germ and endosperm. Generally when we buy rice, it only contains the last of these three, the starch-rich part. And the secret of cooking rice perfectly lies in controlling this starch. Essentially, when rice cooks, it tends to release its starch, which forms a “glue” and tends to stick the rice together. In sushi, the grains must stick together, but at the same time, they must also hold their shape and not become too soft. It's quite a problem! To solve it, the trick is to choose the right rice: it must be a short-grain variety. In other words, it should be round, with a length about the same as the width. Investing in "sushi rice" is a good solution, but if we pay attention to the shape of the grain, we can also choose other varieties, perhaps a risotto rice such as “Roma”.

And we also need to take a look at the nutritional information on the packaging: the percentage of protein must be no more than 6%. The next step is to rinse the rice (until the water runs clear) and to cook it in a small amount of water, with the lid on. This will facilitate the release of amylose, creating the right amount of “glue” to stick the grains together, but without creating a mushy mess. Once cooked, the rice should be drained and mixed with the special rice vinegar solution, then left to rest in a bowl, covered with a tea towel or a sheet of film, for a couple of hours. Of course, many of the steps in the traditional procedure are missing here, but our aim was to obtain perfect sushi with the minimum of fuss, remember? Now let's move on to the fish.

Here, the most important rule is to use absolutely fresh fish. And once bought, we need to freeze it. Why? Simple: some fish may contain Anisakis, a parasitic worm that is very dangerous to human health. In general it tends to infest swordfish, tuna, sardines, hake, cod, haddock, monkfish and scabbard fish: so that includes a lot of fish used in sushi! However, Anisakis dies at temperatures above 65 °C or below -20 °C. Once it has been frozen for at least 96 hours, the fish can be transferred to the fridge to defrost. Don't wait for it to defrost completely: after a few hours in the fridge, take out the fish and cut it. You won't even need a fancy knife: as it is still partially frozen, it will be easier to cut it into precise, thin slices, which we can then put back in the fridge to finish defrosting.

Now that the ingredients are ready, we can make all the different kinds of sushi we want. One last suggestion for the rolls, which are one of the more complicated types to assemble: before using the sheets of nori, put them in the fridge for a couple of hours (no longer than that). You will find that, if you like, you can even make them without using the traditional bamboo rolling mat. We really are sushi heretics, aren't we!

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