Citrus sudachi is a small, aromatic citrus fruit in the family Rutaceae, commonly known as sudachi. It is a distinct citrus species or hybrid closely related to yuzu and other East Asian citrus varieties, and it is most strongly associated with Tokushima Prefecture on the island of Shikoku, Japan, where it has been cultivated for centuries. The genus name Citrus derives from Latin, referring to citron-like trees, while sudachi (すだち / 酢橘) combines su (酢), meaning “vinegar” or “sour,” and tachi (橘), an ancient Japanese word for citrus. Although its precise wild origin is debated, it likely developed in Japan through selection from older East Asian citrus lineages, possibly involving Citrus ichangensis and Citrus reticulata.

As a food source, Citrus sudachi produces small, green fruits that are harvested before full ripeness and used primarily for their juice and zest rather than as fresh eating fruit. Historically, sudachi has been used in Japanese cuisine as a seasonal souring agent, particularly in Tokushima regional foodways. Its juice is squeezed over grilled fish such as Pacific saury, added to noodle dishes like soba and udon, incorporated into ponzu sauce, and used in clear soups and hot pots. The zest is finely grated to add bright citrus aroma to sashimi, tofu, and vegetable dishes. Unlike sweeter citrus fruits, sudachi is valued for its sharp acidity, complex aroma, and refreshing bitterness. Commercially, it is also processed into bottled juice, flavored condiments, and specialty beverages.

Chemically, Citrus sudachi contains significant bioactive compounds typical of aromatic citrus fruits. It is rich in citric acid, the primary organic acid responsible for its sour taste and preservative qualities. The peel contains high concentrations of volatile monoterpenes such as limonene and γ-terpinene, which contribute to its characteristic fragrance and are strongly odorous and flavor-active; these compounds are relatively heat-sensitive and may volatilize during cooking. Sudachi also contains flavonoids such as hesperidin, narirutin, and sudachitin, a polymethoxylated flavone that has been studied for potential anti-inflammatory and metabolic regulatory effects. Vitamin C (ascorbic acid) is present in notable quantities and is heat-labile. Through its combination of acidity, volatile aromatic oils, and flavonoids, Citrus sudachi plays an important role in balancing rich or oily foods within Japanese cuisine and represents a distinctive regional citrus adapted to culinary acidification rather than sweetness.