How Long Does Sea Urchin Last?

Sea urchin, or uni, has become quite a delicacy lately. Having been consumed in Japan for centuries, if not more, sea urchins as a meal only found their way to western shores in recent years. It’s especially popular as sushi or with pasta. But there are some things you should know about this delicacy. For example, how long does a sea urchin last? For how long is it safe to eat uni?

If you want to eat sea urchin raw, as sushi or sashimi, you should do so within two days of buying it. You can keep it in a refrigerator for up to five days, but then it won’t be suitable to be eaten raw anymore and must be cooked. Freezing sea urchins is not recommended since it ruins the texture.

Seafood can be a complicated matter at best. Most fish, shellfish, and other forms of seafood can be harmful and even lethal if we eat them wrong or if they’ve gone bad. This is also the case with sea urchins. It’s always best to stick to specific rules when it comes to sea urchins. Let’s look at those rules and guidelines as determined and refined by the Japanese over the centuries.

How Long Does Sea Urchin Last?

As with any type of seafood, sea urchins are best eaten as fresh as possible. The absolute ideal would be if you could go out on a yacht, catch a few sea urchins, and prepare your meal immediately. Unfortunately, we don’t all have the option to do that, so we have to work with what we’ve got. But the rule remains: eat it as soon as possible.

Sea urchins, or uni, can be refrigerated for up to five days or frozen for three months. However, the quality of the meat and its nutritional value will deteriorate rapidly when you store it either way.

With that in mind, storing your sea urchins for too long is not a good idea. Eat them sooner rather than later. Experts indicate the following basic guidelines:

  • You can eat uni raw while it’s still fresh. If you want to use uni as sushi or sashimi, do so within two days of receiving your sea urchins.
  • If you are not planning to eat it immediately, you can store your uni in the refrigerator for up to five days. At this point, the meat will have lost its texture, so you can’t eat it raw anymore. You will have to cook it, and uni pasta is a great way to do so.
  • If you wish, you can place your sea urchins in the freezer for up to three months. The freezing process drastically reduced the quality of the sea urchin, so keep that in mind. If you cook it after freezing it, the sea urchin will have wholly lost its unique texture and most of its nutritional value. It’s only good enough to use in sauce by now.

There is a slight exception to the rule. Fresh sea urchins that are still alive have a shelf-life of three to five days, as stated. However, if you buy trays of pre-cleaned sea urchins that have been separated in trays, they can last for up to five to seven days. Though this is more expensive, it is worth it since they will not only last longer but also tend to be higher quality than the live sea urchins.

What Will Happen To Sea Urchins If I Store Them Too Long?

Sea urchins should be prepared and eaten as soon as possible. It’s not the type of food that you buy as a part of your monthly groceries and freeze or refrigerate for when you’re in the mood. The best idea is to buy them on the day you plan to eat them, or one day before at the most, then prepare them immediately.

Sea urchins can rapidly lose their taste, consistency, and nutritional value. Not even refrigeration or freezing slows this down by much. Though the process will stop them from spoiling, it cannot prevent the other things from happening. After only a few days of freezing or refrigeration, your sea urchins will get mushy, much less tasty, and far less nutritious.

Two things that make uni so popular are the texture and taste. Uni is often referred to as “the ice cream of the sea” due to its creamy, spreadable consistency. Since sea urchins contain sugar, salt, and amino acids, their taste is described as an “umami-salty sweetness” and is often compared with the taste of sweet mustard.

Both of these characteristics that set sea urchins apart from other foods will be lost if you refrigerate them for more than two days or if you freeze them at all for any length of time.

How Long Will Sea Urchins Last If They Are Alive?

Sea urchins are tiny ocean creatures inside of a spiked shell. You can find them in cold or tropical oceans, but the coldwater variety is more commonly used for meals. That’s partially due to the fact that tropical sea urchins have painful (and potentially lethal) stings to defend themselves. They are also safe to consume, though.

But this gives us some background on one way to potentially make sea urchins last longer. If you have some way to keep them alive, then harvest them when you want to eat them, that would be ideal. For that to happen, you must simulate their natural environment as closely as possible.

Many people who get sea urchins to prepare and eat on a yacht will make some kind of cage and hang them over the side of the boat until they are ready to eat them. This is an ideal situation. Some sushi or seafood establishments will have saltwater tanks with living sea urchins in them. Since sea urchins can easily get to be 100 years or older, this is quite an effective method.

This is not necessarily practical to do in your home, though, especially if you only plan to eat uni occasionally. A tank with a bunch of living sea urchins won’t make sense in that case, especially since they will breed, and you may end up with an unintentional sea urchin farm. You can’t easily stop them from breeding since the part you eat is actually part of their reproductive system.

Keeping Sea Urchin Alive – How To Keep Them Fresh For Longer

If you absolutely have to keep your sea urchins fresh for longer than two days, the best way to do so is to keep them alive. You don’t have to simulate a complete living environment, like in a tank, to do so, but you have to get close to it for a few days.

To do so, place your living sea urchins in a container with cold water with temperatures around 5oC (40oF). This temperature must be maintained at all times, and you will have to keep the water out of direct sunlight or weather conditions like wind and rain.

The cold water itself will be good enough for around seven days, but sea urchins are not meant to live in freshwater. So to keep them alive for even longer, mix in reasonable quantities of salt (the exact amount will depend on the saline levels of the water in the environment the sea urchins originated from.) This process can, in theory, keep sea urchins alive for a few weeks.

Experts believe that you can keep them alive even longer in this way if you find ways to get the algae that they need to survive in there with them, but by now, we are getting close to setting up a tank, and that’s a different matter entirely.

Will Sea Urchins Be As Good If I Do It This Way?

Opinions differ, and the correct answer is, “it depends.” The crucial point that makes the difference is the fact that you will have to clean living sea urchins yourself, whereas they will already have been professionally cleaned if you buy your uni in a box.

Because of this, most people find that sea urchins taste better and are of higher quality if you buy them freshly boxed rather than having to clean living sea urchins yourself. But that depends on how skilled you are at cleaning the sea urchin. Experienced sushi chefs, for example, will probably do a much better job than someone watching a YouTube video tutorial.

shutterstock 599310437

What About Canned Sea Urchins?

Canned sea urchin, often referred to as sea urchin caviar or sea urchin roe, is a rare but effective way to have sea urchin that lasts longer.

Since sea urchins begin to lose their quality almost instantly, a man called Armando Barrio Mata Sr. from Spain first managed to preserve sea urchins in 1948. Though he started doing it only for his family and friends, he eventually turned it into a business that’s still going strong to this day. Conservas Agromar is the world’s leading exporter of canned sea urchin roe.

The processes that Mata and his company use to can the sea urchins are kept secret, and effectively so since other companies have begun doing the same thing, but with a far shorter shelf-life. All we know is that saltwater and lemon are involved in the preservation process.

The result is quite good, too. Though the uni’s consistency and taste are slightly different, and it doesn’t go as well with traditional raw dishes like sushi or sashimi, it is still delicious. It works well with crackers or other meals where uni is traditionally cooked, like kinds of pasta and sauces.

The shelf life of canned sea urchins is still lower than that of other canned foods, but at three years, it’s good enough for most people to include sea urchins in their diet without having to buy them just before cooking.

The price is high, though. It costs around $50 for 5.3 ounces of canned sea urchin roe. But many people say that it is worth the price since the nutritional value and taste of the sea urchin remain almost the same, with the added convenience of having it in a can, ready to eat.

Preserving Sea Urchins While Shipping

One of the most significant challenges with sea urchins is to keep them fresh throughout the shipping process. Despite the rising popularity of uni in the United States, it’s nearly impossible to keep them fresh if they are shipped from Japan, Singapore, or Korea, where they are traditionally from.

The good news is that sea urchins can be found in just about every ocean, so you can find a way to eat fresh, live sea urchins if you live within a one-day drive from any beach in the world. They are sold in high quantities in coastal towns and villages, and some are shipped inland from the local coasts to be sold at fish markets, seafood restaurants, and sushi bars.

As long as the vehicles are equipped with cooling equipment, and the uni is transported in boxes preferably filled with seawater, they can arrive inland on time for you to get your hands on fresh sea urchins.

The other side of the matter is that you can only ever taste sea urchin species from your area. The only way for you to taste what is regarded as the best sea urchin, Kita Murasaki Uni, is to go to Japan and eat it there since it simply will not make the journey to other countries and remain fresh enough to taste and feel the way it should.

To try and solve this challenge to some extent, a company called Corporacion De Fomento De La Produccion registered a patent in 1974 for a system that allows sea urchins to be kept fresh while they are transported.

This process involves placing the sea urchin gonads (pre-cleaned) in a sodium chloride solution after treating them with water, sodium chloride, sodium phosphate, and an antioxidizing agent. They are then quick-frozen and ready for transport.

This process is said to be able to keep the uni fresh for up to six months, which would allow the producers of sea urchins to ship them all over the world, allowing everyone to get a taste of every species of sea urchin.

The state of this patent is unknown, and it’s unclear if the idea was found to be unfeasible or impractical since we still don’t have Japanese uni in fridges anywhere else in the world. But, hopefully soon, that could be a genuine possibility.


Sea urchins, or uni, are becoming more and more popular, and they are easy to prepare. The real challenge is keeping them fresh. However, if you buy them to prepare and eat immediately, you should have no problems. Don’t leave them for longer than two days, though. You can refrigerate them to keep them fresh for up to five or seven days, but never ever freeze them.