Why is it that sea urchin sushi can taste bitter?

What does sea urchin sushi taste like?! 

Sea urchin has a creamy texture and rich flavor, with hints of natural sweetness and seaweed aroma. It leaves a lingering, rich umami flavor on the tongue. The acidity of the vinegared rice perfectly complements the sweetness of the uni. This is the general opinion of people who love sea urchin.

But some people say that “Sea urchin in a wooden box (called ‘hako-uni (箱ウニ)’ or ‘ori-uni (折ウニ)’ or ‘boxed sea urchin’) has a bitter medicine taste”.

The bitterness of sea urchin can be attributed to several factors, including changes in components due to decreased freshness, natural variations in taste depending on species or individual differences, the influence of the quality of seaweed used as feed on flavor, and the use of “potassium aluminum sulfate” (commonly known as alum) to enhance preservation and prevent deformation.

This alum treatment can also impart a distinctive bitterness, astringency, and metallic taste, making it a well-known cause of bitterness. As a result, many high-end sushi restaurants use sea urchin that is labeled as “additive-free” (no alum used).

If you’ve ever tried a sea urchin that tasted bitter*, this may be the reason.

*An “off flavor” that takes away from the primary good tastes.

What is saltwater sea urchin?

Sea urchin soaked in brine without using alum (called ‘ensui-uni (塩水ウニ)’ or ‘saltwater sea urchin’) is also commonly found. There is also a new technology that doesn’t use alum. In this method nitrogen water (water from which oxygen has been removed and then nitrogen dissolved) is used when sealing. The effect of replacing oxygen with nitrogen is inhibited oxidation, maintaining the freshness of the sea urchin.

Since it is sold soaked in saltwater with a salt concentration nearly identical to seawater, it has no bitterness or astringency, allowing you to enjoy the natural sweetness, umami, and seaweed aroma of the sea urchin, as well as its fluffy texture and juiciness. While it has a short shelf life, it is favored by sushi restaurants and high-end Japanese restaurants that prioritize quality. However, it is prone to losing its shape, so handling requires caution, and it is recommended to consume it as soon as possible after purchase.

Related contents:

what is uni?

We hope this information will be helpful.

Revision date: May 21, 2025

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