How To Kombujime (昆布締め)

Kombujime, or konbujime/kobujime, is a fish preservation method used in sushi making. It originally became popular during the Edo period, which gave birth to Edomae style sushi.

Due to the lack of refrigeration technologies in the 1800s, preserving fish was important to prevent illness, as well as an economical way of keeping fish sellable longer. One of the most popular methods to preserve fish is the kombujime method, which is still practiced today at many of the top sushi restaurants in the world.

What Is Kombujime

Kombujime (昆布締め) is a traditional Japanese technique used to prepare fish or other seafood by curing it with kombu, a type of edible kelp. The process involves layering the fish with strips of kombu and allowing it to marinate for a period of time. This method not only imparts a subtle umami flavor from the kombu but also helps to firm up the flesh of the fish while preserving its freshness.

Kombujime is popular at high end sushiyas for its ability to enhance the natural flavors of the seafood while adding a unique depth of taste. It is often used in traditional Japanese cuisine to prepare sashimi or sushi, where the delicate flavor of the fish is highly valued.

Most often the type of fish that utilized the kombujime method were white-fleshed fish aka shiromi, although one can really use any fish that is able to be aged. In the example in this article I show how to do kombujime with kampachi (greater amberjack), which is a great choice for people to begin with as the flavor is delicious and it is a rather easy fish to prepare.

What Fish Can You Use With Kombujime / Kobujime

If we go by tradition the fish most often used with the kombujime method were white fleshed fish called shiromi in Japanese. Just like how red fleshed fish (akami) were preserved with the zuke method and hikarimono were preserved with vinegar.

But these days you can use whatever you want with this method, provided the fish is safe to age in the first place. Some fish that are good to try kombujime for first timers can be:

• hirame (olive flounder / Paralichthys olivaceus)
• tai (red seabream / Pagrus major)
• ginzake (coho salmon)

Preparing Kampachi For Kombujime

In this example I will use kampachi (Greater Amberjack) to show the kombujime method. This is a great fish to cure and is easy to butcher as well, which makes it great for beginners. This fish is often called ‘yellowtail’ but in Japan the true yellowtail is the Japanese amberjack.

Kampachi is one of the easiest fish to fillet, which is good because I used my basic chef’s knife (gyuto) instead of my deba which would be the proper hardware to use here. Using the correct knife is important, but if you don’t have a deba then you should use what you have on hand.

Begin by removing the head by slicing diagonally right behind the front fins. Slice all the way to the spine on both sides, then ‘off with the head’ as they say.

Next make angled slices on the top and bottom of the fish until you reach the spinal column. Make an incision near the tail and slide the knife from the back of the fish to where the head was. You will cut through some small bones, which are easy to remove later.

Then you will have two beautiful kampachi fillets perfect for making kombujime!

Finally use your knife to cut away the belly bones while preserving as much meat as possible. Use fish tweezers to remove the bones you previously cut through et voila you have two skin on, boneless fillets of greater amberjack!

Skin On Or Off?

Traditionally this method leaves the skin on the fish. Scalding water is quickly poured over the skin and then the fillet is plunged into ice water. This tightens the flesh and helps release some of the fat underneath the skin.

Kampachi is a rather firm-fleshed fish with little fat content so for this example the skin was removed. It is entirely up to you if you want to remove the skin now, or later, or keep it on completely and slice fish for some aburi action later on.

Making Kombujime For Aging Fish

To make kombujime you need to first soften the kombu. Place your pieces of dry kombu in a bowl of salt water until they are soft and rehydrated. Depending on the thickness this can take anywhere from five to twenty minutes.

Lay down some plastic wrap on your workspace, followed by a layer of seaweed. Sprinkle a little salt on the seaweed directly, but not too much. You also don’t need to overlap the seaweed much; You only need enough for a layer to completely cover the fish.

Place a top layer of kombu along with a sprinkle of salt over the fish and wrap up with the plastic. Make sure to press out as much air as possible, but do not smash the fish. Then place the neat little packet into the fridge to age.

How Long Should Fish Be Aged With Kombujime

With proper packing and storage you can safely age fish with kombujime for a week. Professionals can of course age for longer, but it becomes more risky to do, so for home use aim for no more than a week and if it smells fishy or rotten then discard.

For your first time aging fish in this method I recommend aiming for 1-3 days. If you make multiple packs you can see how the flavor and texture changes from one day to the next. The longer the fish is in between the kombu the richer the umami flavor will come through.

Sushi Terms Used In This Article