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

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Knowing how to properly freeze ingredients is a great help when you tend to have ones that you couldn't use up or are stuck having to cook with what you have at home.

Yet we often hear that freezing food makes it less tasty.

You'll learn all about the fine art of freezing in our five-part series, starting with this installment.

To start off, we chose a soup packed with frozen vegetables. If you have chopped vegetables in the freezer, you can use the desired amount at any time.

But Kazuhito Kajiwara, former professor at the Tokyo University of Technology who specializes in the study of food preservation and supervised the cooking science aspect of the recipe, has a few words of caution.

The trouble with freezing, he says, is that when the moisture in food becomes ice it damages the food's taste and texture, so you must parboil the ingredients before freezing or take care of the speed and temperature range of thawing when making dishes such as salad.

(For more on this, see his Cookery Science section below).

On the other hand, soup or other dishes where the ingredients are simmered until tender taste great even if you freeze them and cook them as they are.

“You could use small amounts of many kinds of vegetables and create variation in the menu,” says Akiko Watanabe, who supervised the cooking aspect of the recipe.

HOW TO PRESERVE TEXTURE AND COLOR

Vegetables with high water content tend to lose texture and color through freezing. According to Kajiwara, this occurs because the water freezes and damages their cells, as well as due to the profound impact of the tissues deteriorating through the chemical reaction of enzymes and oxidation.

You can curb those effects by somewhat softening the vegetable tissues or stopping the activity of the enzymes in advance. More specifically, blanching, where you boil the ingredients for 20 to 30 seconds before freezing, is effective and many frozen vegetables on the market have gone through this process.

After blanching, you should cool the vegetables, drain and cut them into appropriate sizes before freezing.

BASIC COOKING METHOD

(Supervised by Akiko Watanabe in the cooking aspect and Kazuhito Kajiwara in the cookery science aspect)

* Ingredients (Serves 2)

60 grams (frozen) onion, 20 grams (frozen) celery, 50 grams (frozen) "shimeji" mushroom, 4 (frozen) cherry tomatoes, 1 clove (frozen) garlic, 1 slice (frozen) bacon, 1 Tbsp olive oil, 1 tsp granulated consomme soup base, bit of salt and pepper

About 120 kcal and 1.3 grams salt per portion

1. [Freezing appropriate amount of ingredients]
Cut onion into dices 1 cm on a side. Remove strings of celery stalk and cut into 1-cm cubes. Remove hard end from shimeji mushroom and separate roughly.

Remove calyx from cherry tomatoes. Peel thin skin of garlic, cut off root end. Cut length of bacon in half and wrap convenient number of slices in plastic wrap.

Place each ingredient in storage bag for freezing and push out air. Lay in flat container and freeze (PHOTO A).

2. [To make vegetable soup with ingredients listed above]
Cut length of shimeji in half. Cut bacon into 1-cm cubes. Quarter cherry tomatoes. All may still be frozen.

3. Place oil and garlic in pot on low heat. Briefly cook bacon, then add onion and celery in frozen state (PHOTO B).

Add shimeji, tomatoes, 500 ml water, soup base and bring to a boil over medium heat (PHOTO C). Lower heat, place lid and simmer for 15 minutes. Add salt and pepper to taste.

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Akiko Watanabe is a cooking expert specializing in Japanese cuisine.
Kazuhito Kajiwara is a former professor at the Tokyo University of Technology who specializes in the study of food preservation.

ARRANGED VERSION

Vegetable chowder (Serves 2)

The same amount of frozen vegetables (not including tomato and garlic) as used in the vegetable soup. Cut shimeji and bacon as in the vegetable soup. Melt 15 grams butter in pot, cook bacon, mix in 2 Tbsp flour and add onion, celery and shimeji.

Add 400 ml water and 1 tsp granulated consomme soup base and bring to a boil over medium heat. Lower heat and simmer for 15 minutes while mixing occasionally. Add 200 ml milk, cook for 1 to 2 minutes and add some salt and pepper.

COOKERY SCIENCE

When fresh vegetables or raw meat and fish are frozen, the water content turns into ice crystals. When this happens, the volume increases about 1.1 times, crushing the cells and damaging them. This spoils the texture and causes the savory "umami" flavor and nutrition to drain away. This process is known as “dorippu” in Japanese. A key to freezing is to take effective action against this phenomenon.

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From The Asahi Shimbun’s Gohan Lab column