We will first explain how the deliciousness of fish is understood scientifically. Then we will explain why fugu (pufferfish or blowfish) is so delicious. In general, the deliciousness of fish, or the taste of fish meat, is thought to be related to four main factors.
(1) The type and content of umami components
(2) The type and content of lipids
(3) Texture
(4) Aroma
When eating fish raw, such as sashimi, factors (1) and (2) are of course important, but (3) is also a very important factor. However, the difficulty with sashimi is that there are big differences in how it is perceived depending on regional differences and individual eating habits. Some people prefer the crunchy texture of fish that has just died and still has some stiffness in the flesh, while others prefer the taste of fish that has been maturing and has a more mature flavor, even if the flesh is soft.
(4) is called orthonasal or retronasal, and we can not only smell the aroma from the tip of our nose but also smell it as it passes from the throat to the nasal cavity while we are chewing the food in our mouth. However, in the case of fish, it seems that ultra-trace chemicals determine the smell, and it is currently impossible to measure it quantitatively. It is also said that there are several hundred thousand types of odor substances, but there are only 400 types of human olfactory receptors. In other words, unlike the sense of taste, which corresponds strictly to specific components, the sense of smell is thought to be a form of gradual pattern recognition. Since various odor components are mixed together, this is also the reason why fish have a complex smell that is rare.
On the premise that the concept of deliciousness is largely subjective, we will look at the question of “what determines the deliciousness of fugu”.
The characteristics of fugu that are often said to make it delicious include “light white flesh,” “the umami increases as it matures,” “low in fat,” “the sashimi has a good texture,” and “fugu is the king of hot pot dishes”. Looking at the data in the Standard Tables of Food Composition in Japan, fugu is outstanding in that it has low-fat content, but in other respects, it does not have any particular umami components that stand out, and the total amount of amino acids is also an average figure.
So where does the umami that is unique to fugu come from?
Generally, the umami content of fish increases when it is matured for half a day to several days after it has died, and this is particularly true of fugu. Let’s take a closer look at the umami content, fat content, and texture of fugu.
① Umami ingredients
The main ingredient that contributes to the deliciousness of fish meat is amino acid, and it is thought that the substances called free amino acids determine the taste. Of the free amino acids, glutamic acid contributes to the umami and sweetness, and when the amount of glycine, alanine, proline, etc. is high, the sweetness is felt more strongly. The sweetness here is different from the sweetness of sugar and is a sensation that can be expressed as the umami, richness, mellowness, and thickness of the taste of the food.
Another important amino acid is Inosinic acid, which is known to act as a flavor enhancer rather than as a taste in itself. The synergistic effect of glutamic acid and inosinic acid on umami has been proven in many foods, such as kelp and bonito flakes. Inosinic acid is almost non-existent in living fish, but after the fish dies, ATP, which acts as an energy source, is broken down, and inosinic acid increases in the fish for a certain period. After cooking a fugu, maturing it for a while has the effect of greatly increasing the amount of Inosinic acid. Although Inosinic acid is an important umami component, it is said to be difficult to quantify for each type of fish because it increases and decreases over time, and there are large individual differences. It is also known that it fluctuates greatly depending on the growth history of the fish, such as what kind of environment it grew up in and what it ate, as well as how it was killed and the stress it was subjected to during the killing process.
② Fat content
The most distinctive feature of fugu from the perspective of food composition is that the fat content of the flesh is extremely low, at less than 1%. While most fish store fat in their flesh as they grow, fugu flesh contains almost no fat. However, this does not mean that fugu has little fat in its body as a whole, and it is known to store a lot of fat in its internal organs such as the testes and liver. The detailed mechanism is not known except that it is related to factors involved in lipid accumulation, but the distribution of fat in the body of fugu is different from that of other fish.
Among the fats in fish, the important ones for sensing taste are the omega-3 polyunsaturated fatty acids such as EPA and DHA, one type of so-called long-chain fatty acids. These have a low melting point, so they melt quickly on the tongue and spread easily, affecting the richness and fullness of the taste and the smoothness of the texture on the tongue.
As you can see, while fish fat has some positive aspects, it also has some negative ones, such as greasy. In the case of fugu, the fact that it has little fat in its flesh is thought to have two main advantages.
One is that the fat makes it harder for umami ingredients such as amino acids to be masked. This is strongly suggested by the structure of the human tongue. For example, if the lean meat and fatty meat of tuna have the same level of deliciousness, the lean meat will have a stronger umami taste, but the fatty meat will tend to have a stronger fat taste than umami (research results show that fat itself has no taste). As there is almost no fat in the meat of fugu, it is thought that the umami of the fish meat can be directly tasted.
Another important point is that it is not easily affected by the oxidation of fat. One of the umami components, Inosinic acid, increases after the fish has died, but before the Inosinic acid has increased sufficiently, the long-chain fatty acids oxidize quickly, causing the unpleasant smell known as “fishy smell” to appear and the color to change, spoiling the taste. In contrast, the meat of the fugu contains very little fat, so you can take your time maturing it slowly without worrying about the oxidation of the fat, and bring out the umami components.
③ Texture
Of all the fish, fugu has the hardest flesh. What is particularly worth noting is the unique crunchiness when eaten raw, such as in sashimi, and the hardness of the flesh when chewed. The crunchiness of fish meat is determined by the way the myofibrillar proteins (actin and myosin) that make up the muscles are connected, and also by the type and content of the connective tissue proteins (mainly collagen) that connect them.
Looking at collagen, it is said that the flesh of fugu contains more than double the amount of collagen compared to common fish such as red seabream and sardines. This is why it has a firm texture, and it is possible to make sashimi that is so thin that it is almost transparent. On the other hand, it could also be interpreted that it is too hard to eat unless it is cut thinly.
In addition to the high collagen content, it has also been found that the rate at which the flesh of fugu softens after the rigor mortis has dissipated is slower than any other fish. In general, the flesh of fish becomes softer after rigor mortis has dissipated, but this is related to the decrease in type V collagen. It is said that the solubilization of collagen in fugu is less than that of other fish, so even after death, when some degree of maturing has occurred and a large amount of inosinic acid has accumulated, it still has sufficient firmness to be eaten as sashimi in thin slices. In this respect, too, fugu is suited to maturing.
Incidentally, collagen itself is just connective tissue, so it has almost no taste. Also, the proteins that contain collagen will denature when heated, so when you eat it after heating it, you will enjoy the soft texture rather than the crunchiness.
Before we come to our conclusion, we would like to inform you of the current situation surrounding fugu so that you do not misunderstand it as a fish that endangers your life. Between 2014 and 2023, there were 235 cases of food poisoning caused by fugu, and 5 of these people died. Most of these cases were caused by amateur cooks who lacked the necessary expertise and skills. Fugu poison is colorless, tasteless, and odorless. Therefore, it is impossible to tell whether or not fugu poison is present by sensory means. In addition, the fugu poison is highly heat-resistant and cannot be detoxified using ordinary cooking methods. For this reason, fugu must be prepared by someone with specialist knowledge and skills and a cooking license. Conversely, you can just eat it at a restaurant that specializes in fugu.
To conclude, in the case of fugu, the umami component increases over time, and the fact that the flesh contains little fat means that it is less likely to oxidize, and the fact that it retains sufficient firmness means that it is easier to perceive the umami than with any other fish. And even when heat is applied, the combination of the moderate elasticity and the dashi produced by the other ingredients results in an unparalleled taste. This can be said to be the fundamental part of the deliciousness of fugu.
For your reference.