First, I have to remove the salt from the kazunoko (called “shionuki” 塩抜き) by soaking it in weak salted water (I taste the salted water; just a nice salty taste you can drink if you wanted to). Although you could start with water and then finish “shionuki” with salted water. I prefer to use salted water from the beginning and change it several times in 3-4 hour periods. The reason is that if you remove the salt completely, kazunoko will taste “bitter”. So, you need to leave some saltiness behind. Using salted water prevents the complete removal of the salt even if you forget and soak it too long. While soaking, I removed the thin white membrane which covers the roe by rubbing the surface with my finger tips under water. After “shionuki” and removing the membrane, herring roe is ready as shown in the lower left image. I tasted a small piece from the edge to make sure it is not too salty. I sometimes thinly slice this and serve it like sashimi with wasabi and soy sauce but I usually marinate it.
For the marinade, I make dashi broth from a kelp and bonito dash pack. I season with light colored soy sauce (to preserve the golden color) and sake. The amount of sake (or mirin if you like it sweet) and soy sauce are up to your taste but I tend to make a strong dashi packed with “umami” and go light on soy sauce. I gently boiled the mixture for few minutes to make sure the alcohol has all evaporated and tastes amalgamated. I let it cool to the room temperature and then refrigerate. I marinated the prepared herring roe for, at least several hours or over night in the refrigerator (The right lower image shows the roe after marinading). You should eat this in few days.
I sliced it into small bite sized pieces and then mixed them with dried bonito flakes or kezuribushi 削り節 and served. It has a very interesting crunch and is an excellent drinking companion for cold sake. After eating it, my wife asked, “Why does it suddenly feel like New Year?”