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

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Adding sugar or sweet mirin sake to a dish gives it a subtle sweetness and turns the flavor up a notch.

Seasonings that add “sweetness” are the focus of our next four-part series starting this week. Using different ones lets you enjoy variations not just in flavor, but also in aroma and appearance.

First up in our series is “nikorogashi,” which is seasoned simply with sugar and soy sauce. The sweet-salty taste of the potato crumbling in your mouth is quite irresistible.

After the potato has been simmered until seasoned and soft, the lid on the pot is removed to cook out the liquid.

Though it is called “nikorogashi” (“niru” is to simmer and “korogasu” is to roll), the potato pieces are rolled only when sauteing.

After adding the simmering liquid, turn the potatoes once or twice, and move the pot only occasionally. This way, the pieces won't fall apart when they're simmering.

A key is to avoid pouring the seasonings directly onto the potatoes as that will flavor them unevenly. If you add the seasonings to the liquid instead, they will seep in evenly to the core during cooking.

TAKE ADVANTAGE OF JAPAN'S SUGAR VARIATIONS

The main raw materials of sugar are sugarcane that grows in warm regions and sugar beet from cold areas.

In Europe, sugar is mostly used to make sweets and most sugar is the granulated type made from sugar beets, according to Yukie Nagai, assistant manager of the research and development division of Mitsui Sugar Co., who supervised our recipe's cooking science aspect.

In Japan, a variety of sugar is used for different purposes. Caster sugar and “sanon-to” (brown-hued sugar made from molasses that remain after white sugar is made) are used for cooking, while “shirozara-to” (crystalized sucrose) and “wasanbon” (fine golden-colored sugar) are used to make high-end sweets.

“Japan probably has the widest variation of sugars,” Nagai says.

White sugar is white not because it has been bleached, but because light reflects randomly on the surface of the crystals. “Kuro-zato” (muscovado) is brown since it is made by simply boiling down the juice of sugar cane.

BASIC COOKING METHOD

(Supervised by Akiko Watanabe in the cooking aspect and Yukie Nagai in the cookery science aspect)

* Ingredients (Serves two)

300 grams potatoes (May Queen variety), 2 tsp cooking oil, 2 Tbsp sugar, 1 and 1/3 Tbsp soy sauce

About 195 kcal and 1.7 grams salt per portion

1. Peel potatoes and cut randomly. Immerse in water as you cut. When all potatoes are cut, drain in sieve and pat dry with kitchen paper (PHOTO A).

2. Heat oil in frying pan and lightly saute potato pieces on medium heat until coated with oil (PHOTO B).

3. Add 3/4 cup water, and sugar. Cover pot with lid and simmer on low heat for 5 minutes.

4. Turn potato pieces and add soy sauce. Cover with lid and simmer on low heat for 8 to 10 minutes until they are soft enough to pierce with a bamboo skewer.

5. Remove lid and while spooning liquid onto potatoes, reduce on low heat until almost no liquid remains (PHOTO C).

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Akiko Watanabe is a cooking expert specializing in Japanese cuisine.

Yukie Nagai is an assistant manager of the research and development division of Mitsui Sugar Co.

ARRANGED VERSION

Simmered “satoimo” yam (Serves two)

Peel 300 grams of satoimo and immerse in water as you cut the pieces. Place the pieces and water that covers them in a pot on medium heat.

When it comes to a boil, turn down to low heat.

After cooking for 20 to 25 minutes until the satoimo turns soft, drain in a sieve.

Wash pot, add the satoimo, 1/2 cup water and 1 Tbsp sugar, and bring to a boil. Add 1 Tbsp soy sauce. Cover with lid with a small opening and simmer over low heat for 5 minutes. Remove lid and reduce until almost no liquid remains.

COOKERY SCIENCE

The cell membrane of foodstuffs does not allow the seasoning molecules that are larger than those of water to permeate.

But when a foodstuff is heated, the membrane’s structure is broken down, and the seasoning molecules find their way into the cells.

In the case of salt and sugar, if salt is added first, the food will become too salty since salt has a small molecular weight and high transfer rate.

This is one of the reasons that the seasonings should be added in the order of the Japanese syllabary characters "sa shi su se so" ("sato" [sugar], “shio” [salt], “su” [vinegar], “seuyu” [alteration of “shoyu,” or soy sauce], “miso”).

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From The Asahi Shimbun’s Gohan Lab column