Uni 雲丹 – Sea Urchin

One of the most popular (and expensive) sushi toppings is uni. Uni, or 雲丹, is the Japanese word for sea urchin. These spiky balls may look off-putting, but the creamy, rich tasting meat they have inside is one of my absolute favorite neta.

While sea urchin has been eaten in Japan for millennia, it only became popular in sushi with the invention of gunkanmaki. This is because if you tried to put uni on a nigiri it would just fall off. Thus, you are unlikely to see uni gunkanmaki served at traditional Edomae style restaurants – although some do choose to serve it since it is just so popular.

What Actually Is Uni?

Uni is the edible part of the sea urchin, specifically its gonads. Sea urchins are small, spiny marine animals found in oceans worldwide. The gonads, which can be found in both male and female sea urchins, are harvested and eaten raw or used in various dishes. The texture of uni is creamy, and its flavor is often described as a mix of sweet and briny, with a hint of ocean freshness.

Each sea urchin has 5 gonads, and a high quality gunkanmaki will use five pieces for the topping. Of course, this all depends on the chef and the size of the uni to begin with.

Common Types of Uni

There are several species of sea urchins, but the most commonly harvested for uni are:

1. Bafun Uni (Hemicentrotus pulcherrimus): A rather small sea urchin found all over Japan. It is known for its rich flavor and bright orange color. While this is a widely harvested type of uni, it should not be confused with ezobafun uni, which is one of the two common types of ‘Hokkaido Uni’ you’ll see on premium sushi menus.
2. Kitamurasaki Uni (Strongylocentrotus nudus): Typically larger and less intensely flavored than Bafun Uni, this is also a type of Hokkaido Uni. It is found not just around Hokkaido, but down to Tohoku and other areas of northern Honshu. This is one of the most premium types of uni, and it can be seen by the high price. It has a rich color and briny taste which pairs wonderfully with the sour taste of properly made sushi rice.
3. California Gold (Strongylocentrotus franciscanus): This sea urchin is found along the Pacific coast and is known for its buttery texture. It is mainly harvested around Santa Barbara so it is commonly called Santa Barbara uni. This is a type most commonly seen in USA at sushi restaurants as it is less expensive than importing uni from Japan.

How Is Uni Processed?

Uni harvesting and processing is a meticulous and labor-intensive process that begins with divers or fishermen carefully collecting sea urchins from the ocean floor. These sea urchins are often found in rocky coastal areas and are gathered using specialized tools to avoid damaging their delicate shells. Once harvested, the sea urchins are transported to processing facilities, where they are carefully cracked open by skilled workers to extract the gonads, or uni.

The uni is then meticulously cleaned with salt water to remove any impurities, ensuring only the highest quality product. After cleaning, the uni is graded based on color, texture, and freshness, with the best quality uni reserved for sushi and sashimi. Finally, the uni is packed in wooden trays or plastic containers, often with a small amount of saltwater or a preservative solution to maintain its freshness, before being distributed to restaurants and markets around the world.

Preservative Solution?

The preservative solution used in the processing of uni is typically a saltwater brine. This brine helps to maintain the freshness, texture, and flavor of the uni during transportation and storage. The saltwater brine mimics the natural ocean environment, which helps to preserve the delicate structure of the uni and prevent it from spoiling. Some processors may also use a mild citric acid solution, which acts as a preservative by lowering the pH and inhibiting bacterial growth. However, the primary preservative solution is usually a carefully balanced saltwater mixture designed to keep the uni fresh and flavorful until it reaches the consumer.

Less commonly used these days is potassium alum, which was popular in the past but now is mostly seen with low quality uni, or packed uni from China.

How To Make Uni Gunkanmaki

Making uni gunkanmaki is no different than any other gunkan type sushi. You start with a small mound of rice, about 1.5x the amount you would use for a nigiri. Shape it into an oval and place it on your cutting board or workstation. Wrap a strip of nori around the rice, then gently push down on the rice so the nori remains taut and evenly spread.

In the opening of the gunkan you can place your uni. I suggest using chopsticks to move the uni from the tray to the gunkan, taking care not to smash the urchin too much. Also, try to prevent the uni from resting on top of the edge of the seaweed or it will soften it to collapse. Each gunkanmaki should have 5 pieces of uni, although if they are particularly large or small you can adjust to suit your needs.

Garnish?

I rarely garnish uni gunkanmaki as I think the fresh, sea and umami taste of the urchin pairs perfectly with the vinegared rice. However if you want to add a garnish you can pretty much add whatever you like, from caviar to hojiso flowers.

Sushi Terms Used In This Article