What are Bonito Flakes & Why Bonito Flakes Moving?

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Japanese food has become very popular in recent years. Not only is it fresh and healthy, and suitable to most diets, but it’s also tasty. In fact, you can also adapt it to different diets, such as gluten-free or vegetarian.

With the advent of Japanese food, many people have begun to purchase the basics for cooking these oriental meals at home. There are many ingredients to source, and most will be unfamiliar to Western kitchens. But there is one ingredient that is a little puzzling, however, and that is Bonito flakes.

When you put it on food, it starts waving around, which could be unnerving for some people. However, it’s perfectly normal. There is no need for alarm. This article will explain why that happens, and help to reassure the nervous cook.

Firstly, however, it’s important to mention the range of basic items required for cooking Japanese dishes. Then we’ll ascertain how Bonito flakes fit into the mix, and discuss what it does for the dishes.

Typical Items of Japanese Cuisine

There are several basics that are used in most Japanese cooking:

  • Soy sauce
  • Miso
  • Katsuobishi, or Bonito flakes
  • Rice wine vinegar
  • Mirin
  • Sake
  • Sesame oil
  • Japanese usta sauce
  • Konbu kelp
  • Japanese hot mustard

You would need to purchase them all if you’re going to cook Japanese food regularly.

However, the focus on this article is on Bonito flakes, and we’ll now focus on it, so you can understand what it is and why it moves around when on food.

Bonito Flakes

What are Bonito Flakes?

What are Bonito Flakes
Credit: @wearesaitaku

Bonito flakes, known as Katsuobushi in Japan, is made from skipjack tuna. This fish is dried to a moisture content of 20%, and shaved into wafer-thin flakes.

How are Bonito Flakes Made?

Skipjack tuna is caught, gutted, and decapitated. Each fish is cut into four, and then simmered for a couple of hours in hot water. It’s then cooled and deboned, and immediately smoked with oak. In doing so, phenols are deposited onto the surface of the fish, and sink in when drying further. Phenols in food are associated with flavors and aromas. It’s then smoked and cooled for another month.

The cooling allows the moisture in the fish to evaporate, and the skipjack ultimately becomes rock-hard. It then gets shaved and placed in plastic bags. Traditionally, you would use a special shaver to shave it yourself. The modern Japanese home-cook does not have the time or energy for this task, and so manufacturers now place it in plastic bags for consumers’ easy usage.

Why do Bonito Flakes Move When Put on Food?

The flakes are used in soups, stews and as garnish. When used as a garnish on hot food, it starts moving around, dancing as though moved by an ocean current because:

  • Firstly, the fish is rehydrating from the steam, and moves as a result
  • Secondly, the wafer-thin flakes are moved around by the steam, causing them to wave around.

The Nutritional and Flavor Value of Bonito Flakes

These flakes are high in protein, and low in saturated fat. In terms of flavor, the following applies to these flakes:

  • It’s high in disodium inosinate and disodium guanylate, two compounds associated with good flavors.
  • When combined, these two compounds form disodium ribonucleotides.
  • The latter enhances the effects of glutamates, which stimulate the tastebuds in a pleasant manner. The combination of all of these compounds makes food taste exquisite.

What are Bonito Flakes Used For?

The fish flakes are used for decoration, or to add flavor to a meal, but most popularly, it’s used as a base for Japanese soups and stews. The stock is called Dashi. Usually, the flakes are added to boiling water, and then filtered out. It not only has a strong flavor of its own, but it also brings out the flavor of other ingredients.

What are the Health Benefits of Bonito Flakes?

There are a number of health benefits of eating Bonito flakes, some proven in studies, and others merely traditional claims:

  • Anti-aging: The Dashi contains iosinic acid, which activates the cells of the body, which should lead to the benefits of anti-aging products. They also contain amino acids that the body cannot produce, and which create collagen—an anti-ageing substance.
  • Relief from fatigue: A study has been done which claims dashi made with bonito flakes may improve mental performance and reduce fatigue.
  • Lower blood pressure: Another study demonstrates that daily ingestion of bonito broth lowers blood pressure and improves the emotional state of a person.
  • Decreasing obesity and reducing inflammation: A further study has shown that a fermented extract of bonito reduces obesity and decreases inflammation in mice. Yet further hypotheses abound that bonito results in the same feeling of satisfaction that fats and sugars induce in westerners. This in turn results in less weight-gain.

A Bonito Recipe


  • 1L of water
  • 20 g Kombu kelp
  • 25 g Bonito flakes


  • Cut a few slits into your kombu and add it and the water into a saucepan. Soak for between 30 minutes and 12 hours.
  • Bring it to a near-boil, skimming off impurities occasionally.
  • Once close to boiling, take it off the heat and remove the kombu. Allow the liquid to cool a little.
  • Add the bonito flakes to the water and bring it to the boil.
  • Once boiling, reduce the heat and simmer for 30 seconds.
  • Let the flakes sink to the bottom. This can take around 10 minutes.
  • Strain the dashi.
  • Now drink as desired.

In Summary

Bonito flakes are an unusual form of smoked fish that is shaved into flakes. These flakes move around when put on food because of their dehydrated and wafer-like nature. It’s not something to worry about. Instead, the flakes are highly nutritious and beneficial for your health, so why not use them more from now on?

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