1. How Ikeda Kikunae Discovered the Umami Taste in Kombu
Kombu dashi has been enjoyed for a long time, but for many years, no one knew exactly what created its taste. In 1907, Ikeda Kikunae decided to study the umami in kombu. The following year, in 1908, he identified that the umami component was glutamic acid [1]. Ikeda is said to have been convinced that kombu dashi had a taste different from sweet, salty, sour, or bitter flavors. He named this taste "umami" [2]. Glutamic acid is a type of amino acid.
For a long time, a story was widely known that Ikeda got the idea for his research when he saw kombu his wife had bought. However, recent theories suggest this may not be true. Some explanations state that because he was familiar with kombu dashi from childhood, he had been interested in its umami since he was young [1]. It is not decided here which explanation is correct. What is clear is that glutamic acid is the center of kombu's umami. To understand the other dashi ingredient, bonito flakes, we must first look at what they are.
2. Why Bonito Flakes Are Boiled, Smoked, and Mold-Cured
Bonito flakes are made by boiling bonito meat and drying it while smoking it. The drying process continues until the moisture is 26% or less, which is about one-quarter [3]. According to the Ministry of Agriculture, Forestry and Fisheries, the process begins by boiling the meat at about 80°C for 60 to 90 minutes. This step is called "shakunetsu" (boiling). After that, the meat is smoked and dried in a process called "bakkan," which is repeated 10 to 20 times [4].
Mold plays a key role in this process. By repeating smoking and applying mold, the moisture decreases further. It is thought that this creates an environment where microorganisms cannot grow, which improves preservation [4]. Flakes that have had mold applied at least twice are called "hongarebushi". For hongarebushi, the surface is shaved to apply mold, and the flakes are then aged for about 4 to 6 months [3]. The time for applying mold and aging varies depending on the source or the maker, so this article follows the description on the Ministry of Agriculture, Forestry and Fisheries page. Bonito flakes are hard and light because they have very little water. Making bonito flakes is also a method for preserving fish for a long time.
3. Inosinic Acid: The Umami Component in Bonito Flakes That Differs from Kombu's Glutamic Acid
The center of the umami in bonito flakes is a component called inosinic acid. This is a different substance from the glutamic acid found in kombu. The Encyclopedia Nipponica states that inosinic acid is the main component of the taste in bonito flakes [5]. It is said that Kodama Shintaro discovered this. In 1913, he found that histidine salt of inosinic acid had umami as one of the umami components in bonito flakes [5]. This was about five years after Ikeda Kikunae studied kombu. Glutamic acid from kombu and inosinic acid from bonito flakes have different names and come from different foods. These two components are used in Japanese dashi. What happens to the strength of the flavor when these two are put together?
4. How Mixing Kombu and Bonito Flakes Creates the Umami Synergy Effect in Dashi
When glutamic acid from kombu and inosinic acid from bonito flakes are present together, the umami becomes stronger. This is called the "synergy effect of umami" [6]. Guanylic acid from dried shiitake mushrooms is also one of the umami components. Regarding how much the flavor increases, school lunch materials from Kawasaki City explain that combined dashi made with kombu and bonito flakes has "more than double" the umami [7]. It is said that the way the multiplier is stated varies by source, but this article introduces the "more than double" figure from the Kawasaki City materials. The number "double" is not a number that counted how it feels, but a direct introduction of the explanation in the materials.
The same materials also explain how to make combined dashi. Put 4g of kombu and 40g of bonito flakes into 1.2L of water and soak them for at least 30 minutes. Remove the kombu just before it boils [7]. If you divide these amounts by four, you get a small portion for home use: 300mL of water, 1g of kombu, and 10g of bonito flakes. The ratio remains the same because 4g divided by 4 is 1g, and 40g divided by 4 is 10g. How can you compare the difference in taste with your own tongue?
5. How to Compare Kombu Dashi, Bonito Dashi, and Mixed Dashi at Home
If you have kombu and bonito flakes at home, you can make and compare three types of dashi with an adult. Put only kombu (1g), only bonito flakes (10g), and both (1g kombu and 10g bonito flakes) into 300mL of water each. Soak them for at least 30 minutes, following the "soak for at least 30 minutes" instruction from the Kawasaki City materials. When heating them, an adult must handle the fire, and you must be careful of burns. Remove the kombu just before it boils, following the procedure from the Kawasaki City materials [7]. Using the same procedure for all three makes them easier to compare.
Do not add salt or other seasonings. Taste them little by little and try to describe the differences in words. Since the way taste is felt differs from person to person, it is not a mistake if you do not feel it as "double." The amounts for kombu only and bonito flakes only are a method of trying this out in this article, using the logic from the Kawasaki City quantities. Read the sources: the National Diet Library page on Ikeda's discovery and the Ministry of Agriculture, Forestry and Fisheries guide on making bonito flakes are available. The Kawasaki City materials allow you to verify the method for making combined dashi directly.