What is Uni ウニ 【雲丹】?
Uni represents in Japanese the class of sea-urchins which belong to the Echinoderms. Worldwide there are up to a thousand species, but only a small part of them is valued as food. The gonads (reproductive glands) of the uni, also occasionally referred to as roe, are considered a delicacy in Japan and many other regions of the world. Uni is considered one of the most popular sushi ingredients in Japan.
The characters 雲丹 (uni) are used to indicate the food produced from the gonads of the sea urchin. Translated, they are understood as “vermilion cloud” and describe as a metaphor the appearance of the food.
Uni for Sushi and Sashimi
The raw gonads of the uni have an unmistakable taste. The exceptionally full-bodied umami taste is accompanied by mineral, sweet and slightly salty aromas reminiscent of the sea. The texture is extremely soft and literally melts on the tongue. Although uni can be eaten wonderfully on its own, it also tastes very well in combination with normal or vinegared rice. The most important factor for the good taste is freshness. Fresh uni has a pleasant and hardly noticeable odor. However, if stored too long or incorrectly, it has an unappetizing fishy smell and taste. For this reason, cheap, industrially processed or uni intended for export is enriched with alcohol or other preservatives (e.g. alum), which also have a negative effect on the taste. Another important factor is the nutrition of the sea urchins, as this influences the taste and the size of the gonads. Since the main component of their diet consists of seaweed, it is obvious that tasty sea urchins are mainly found in regions known for their seaweed quality ([Takagi et al., 2017], [Takagi et al., 2020]).
As Sushi, uni is prepared either as “battleship-roll” (gunkan-maki) or “hand-pressed” sushi (nigiri-zushi). Although it is a high-priced ingredient, it is today part of the standard repertoire in many sushi restaurants. The combination of uni and ika is popular, either as a side dish or by placing uni in small quantities on the ika meat. Ikura, the fish roe of the salmon, is also a popular side dish (e.g. uni ikura kaisen-don).
The best season for sea urchins is very much dependent on the species and region. All species preferred in Japan vary so much throughout the year that uni can be eaten in good quality all year round. For example, ezobafun-uni is in season from spring to autum and kitamurasakiuni is in winter. Sea urchins caught on the coasts of Europe, the United States and Canada are particularly tasty during the winter months [Seafoodwatch, 2008]. Uni from sea urchins, which was fished out of season, is said to have a bitter and unappetizing taste.
Ensui Uni 塩水海胆
When uni are processed, they are usually broken open, cleaned and sorted before being arranged in the sales packaging. To increase shelf life, industrial preservatives are usually added to the extracted gonads. In ensui (えんすい) or shiomizu (しおみず) processing, on the other hand, the gonads are cleaned and then preserved in a salt solution. This salt water has approximately the same salinity as the sea water of the region from which the uni originate. It is said that this “natural” preservation method better preserves the original taste.
Uni in Japan
The largest market for seafood and sea urchins is the toyosu-shijou market in Tokyo, nowhere else is uni traded on a comparable scale. Every day the daily price is determined at the uni auction (uni no seri). Besides tuna, uni is one of the few products whose price is still determined by auction nowadays. The auction is not a classical auction as it is usually known, in which the bidders bid in ascending order until no more bids are received, instead it is a variant in which each bidder makes only one bid. The contract is then granted to the bidder with the highest bid. The expected price ranges are wide, so uni in low quality is available from 400 ¥, while premium quality can reach 10,000 ¥ and more.Uni is divided into three categories labeled A, B and C respectively. For the preparation of sushi only the top two levels A and B are used. A distinction is also made between color-coded and sorted uni (narabi) and various colored, unordered (bara) packages.
Ezobafun-uni belongs to the most fished sea urchin species in Japan.Ezo is an old Japanese term for the population in the east and north of Japan and refers to the area where ezobafun-uni has been fished since ancient times. In Japanese, bafun stands for the droppings of a horse and is a metaphor for the appearance of this sea urchin species. Even though they are not scientifically classified as belonging to the bafun genus (lat. Hemicentrotus), they are so visually similar that they traditionally bear their designation in their name. The Japanese distribution area stretches from Hokkaido to Sagami Bay. Import goods come mainly from South Korea and the adjacent coastal regions of Russia and China. The gonads have a visible orange coloration, the taste is full-bodied sweet and is highly appreciated in Japan as an ingredient for Sushi.
The gonads of the kitamurasakiuni are visibly brighter than those of the ezobafun-uni, which is why they are also called “white sea urchin” in Japan (shiro-uni). The taste is light and has an elegant sweetness. The distribution area is similar to that of ezobafun-uni. Kitamurasakiuni caught on the coasts of Oma, in Aomori Prefecture, are considered a special delicacy in Japan and are traded at high prices.
Characteristics & Ecology
The spread-area stretches over all oceans and climatic zones, they populate rocky coasts as far as to the ground of the deep sea. Their food consists primarily of algae, but there are also species that feed on carrion, microorganisms or marine snow. Their natural predators are mainly sea otters and starfish. Some species of sea urchins are extraordinarily long-lived. Studies have shown that individuals of the red sea urchin can live up to 200 years [Ebert & Southon, 2003].
Most sea urchins traded on the Japanese market are ezobafun-uni and kitamurasakiuni. In Europe, the stone- and European edible sea urchin is the most common species. In the United States, sea urchins are most commonly served in Japanese sushi restaurants, where mainly purple-, red-, green sea urchins and species imported from Japan are used.
|Japanese name||Common name||Region|
|Pink sea urchin
|Japan, Korea, China, Russia|
|American purple sea urchin
|Alaska to California|
|Red sea urchin
|Alaska to California|
|Short-spined sea uruchin, green sea urchin
|Japan, Korea, China|
|Ezo short-spined sea uruchin, ezo green sea urchin
|Japan, Russia, China|
|Long-spined sea urchin
|Green sea urchin
|Upper northern hemisphere|
|Northern sea urchin
|Purple sea urchin
|Japan, Korea, China|
||European purple sea urchin
|Atlantic and Mediterranean Sea|
||European edible sea urchin, common sea urchin
The increased demand for sea urchins in recent decades has led to an expansion of fishing and overfishing of some species ([Botsford et. al., 2004], [Rogers-Benett, 2007]). Recently, the production of sea urchins in aquaculture has received more attention, especially as it allows to improve the growth and quality of the gonads [Lawrence et al., 2001].