Editor’s note: The theme of Gohan Lab is to help people make simple, tasty “gohan” (meals).

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You might be familiar with tuna, known as “maguro” in Japan, as sashimi or sushi, but if you buy it in a block known as “saku,” would you know how to handle it?

In two installments of summer delicacies, pros from Toyosu Market in Tokyo will introduce ways to enjoy frozen tuna available through such means as online shopping. The chosen ingredient is the “mebachi” (bigeye tuna) type that is more affordable than “hon-maguro.”

But fish that has been frozen in season tastes good whether it is “toro” (fatty) or “akami” (lean).

How you thaw the fish determines the flavor. Our goal is to prevent the umami flavor from dripping out. The drip can be curbed by thawing with speed and keeping the core temperature low when the fish is thawed completely. That is where the “lukewarm saltwater thawing” method used at the fish market comes in. Dropping the whole block in the water may come as a surprise, but water conducts heat better than air and saltwater that is close to seawater retains the texture of the tuna and its vivid red color.

As a final touch, the water on the surface should be wiped thoroughly before chilling. The meat will tighten and offer even more flavor. If you need some for dinner, thaw the fish when you do the washing up after lunch. All you have to do later is cut it.

The installment on tuna was supervised by Shigeo Yokota and Yutaka Kurihara, the chairman and vice chairman, respectively, of Omono Gyokai, a trade group of intermediate wholesalers specializing in tuna at the Toyosu Market. Wholesale dealer Chuo Gyorui allowed us to take photos in their test production room.

Though the upscale “kuro-maguro” (Pacific bluefin tuna) often makes the headlines, the type that dominates the auction held every morning is the frozen “mebachi,” says Yokota. The sound of electric saws that cut them up fill the air at the market.

According to Kurihara, “If you buy frozen tuna, it is best to thaw and eat it within three days if possible, when it tastes the best.”

While commercial freezers can reach minus 60 degrees, freezers at home manage to chill to about minus 20 degrees. Even if the food is frozen, there is a difference of 40 degrees and with time, the quality of thawed food will change, such as the size of the ice crystals.

BASIC COOKING METHOD

(Supervised by Yutaka Kurihara in the cooking aspect and Midori Kasai in the cookery science aspect)

* Ingredients and cooking utensils

1 block (saku) frozen tuna (about 200 to 300 grams), salt, water, bowl, paper towel, flat square container, plastic wrap or bag

1. Pour water in bowl, add 2 Tbsp salt per liter of water to make saltwater with 3-percent concentration. In summer, use water from the tap. As the water temperature is low in winter, add hot water to maintain a temperature of around 25 degrees, feeling warm.

2. Quickly rinse frozen tuna block and remove chips on surface (PHOTO A).

3. Immerse tuna in saltwater in bowl. Leave for 5 to 10 minutes until entire block bends and is about 80 percent thawed (PHOTO B). Remove from water. Change duration depending on the condition of block. If saltwater becomes cold halfway, it is better to change to new saltwater.

4. Pour some water on surface to remove salt, then pat dry thoroughly using paper towel. Wrap block in new paper towel. Place on flat container and cover with plastic wrap (PHOTO C) or in plastic bag for storage and store in fridge.

5. Cool for more than an hour. If paper towel becomes soaked, wrap with new paper.

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Yutaka Kurihara is vice chairman of Omono Gyokai.

Midori Kasai is a professor at Ochanomizu University and chairwoman of the Japan Society of Cookery Science.

ARRANGED VERSION

<Grilled tuna>

There are parts of tuna that are fatty enough but may have thick white tendons that are hard to chew. They are better cooked to the center over low heat. The tendons will turn transparent and jelly-like.

Cut the block into pieces that are 1 cm thick. Sprinkle a bit of salt and cook both sides in frying pan or grill over low heat. Sprinkle with chopped green onion and pour citrus-based “ponzu” sauce. To make teriyaki, marinate tuna in a mixture of same parts soy sauce, sake and sweet mirin sake, pat lightly dry and cook both sides over low heat.

COOKERY SCIENCE

When fish is frozen, ice crystals are formed, but they flow out as drip when thawed. Food is thawed nicely if the drip is kept at less than 5 percent of the volume. In the experiment, this figure was achieved in both cases when the fish was thawed with lukewarm saltwater or in the fridge. The former resulted in less drip. In the sensory evaluation where the fish was observed and tasted, the one thawed with lukewarm saltwater was less black, the meat textured and chewy.

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From The Asahi Shimbun’s Gohan Lab column