Fatty tuna and conger eel, along with squid and shrimp known for their sweetness, are sometimes served with salt instead of nikiri shoyu (soy sauce). A touch of grated yuzu zest or a few drops of kabosu juice are often added for their refreshing aroma.
It can be viewed from three angles: how chemistry shapes flavor, how technique refines timing, and how our senses perceive texture and aroma.
In sushi, using salt or citrus is not merely seasoning—it is a refined technique to balance umami, aroma, and texture delicately.
Salt enhances sushi’s flavor because it does more than just season. Taste receptors in the thousands of taste buds on the tongue’s surface are electrically stimulated by sodium ions from added salt, which send a “salty” signal to the brain. At the same time, sodium ions help glutamic and inosinic acids—the key umami compounds—bind more effectively to the receptors, amplifying the taste response. In other words, salt not only imparts saltiness but also heightens the sensitivity of umami receptors, enhancing the fish’s natural savory flavor.
Furthermore, salt gently draws out excess moisture from the surface of the fish through osmosis. This concentrates umami components such as free amino acids and nucleic acids, while reducing any fishy odor and sharpening the flavor profile.
A small amount of salt is also believed to stimulate saliva production, which helps counter the numbing effect of fat on the taste buds. As a result, flavor compounds reach the tongue more readily, making the sweetness and richness of the fat feel more distinct.
Citrus fruits, on the other hand, are rich in volatile aromatic compounds such as limonene. The refreshing scent that fills the nasal cavity when you chew conveys a sense of freshness. Meanwhile, acidic components like citric acid cut through the heaviness of the fat, leaving the palate clean and refreshed, and making the next piece even more enjoyable.
In essence, salt and citrus engage different senses—the tongue and the nose—not merely adding to sushi’s flavor, but bringing out the ingredients’ natural qualities and creating perfect harmony.