What is natto?
In Japan, natto is a breakfast food, usually eaten on a bowl of warm rice. Before eating, you stir the beans hard with chopsticks until a white, foamy slime forms. Then you season with soy sauce or the sauce that comes in the pack, plus hot Japanese mustard, karashi. The strands are polyglutamic acid, which the bacterium produces during fermentation. In a Japanese supermarket natto comes in small trays of 40 to 50 g. Outside Japan you can usually find it frozen at an Asian grocery store.
The right ingredients
- Soybeans: In Japan, producers use small varieties called kotsubu. Yellow soybeans from a health food store work too, but they need longer on the stove.
- Starter culture: You can order natto spores as a powder online. One packet is enough for many batches. Use the amount on the package and dissolve it in a tablespoon of boiled water. Alternatively, stir a tablespoon of store-bought natto into the beans. Frozen natto works too.
- Sugar: You can leave out the teaspoon of sugar.
How to make natto
Cook the beans until soft
Soak the beans for 12 to 24 hours, until they swell to about double their size. They are done when you can crush a bean between your thumb and ring finger without pressure. In a pot this takes several hours, in a pressure cooker about 40 minutes. Drain the beans well afterwards, because wet beans ferment badly.
Work cleanly
Rinse the container, spoon and lid with boiling water first. Otherwise stray microbes from the kitchen grow alongside the culture and spoil the batch. Sprinkle the culture over the still warm beans and mix it in.
Keep it warm
Spread the beans no more than 3 cm (1 in) deep in a shallow dish. Cover with plastic wrap and poke a few holes in it, because the bacteria need oxygen. To hold 40 °C (104 °F), use an oven with a proofing setting, a yogurt maker, a dehydrator or a cooler with a hot water bottle. Check the temperature with a thermometer. After 24 hours a white film covers the beans, and they pull strands when you stir them.
Ripen in the fridge
Then put the natto in the fridge for at least a day. The strands get longer and the flavor rounder. It keeps there for about a week, or several months if you freeze it in portions.
Common mistakes
- No strands: The temperature was too low or the time too short. Leave the batch somewhere warm for another 12 hours.
- Hard beans: You cooked them too briefly. The culture does not soften hard beans.
- Colorful mold or a rotten smell: Green, black or pink spots mean foreign microbes. Throw the batch away.
Natto dishes
For natto gohan, put a portion of natto with scallions on freshly cooked Japanese rice. The basics are covered under cooking rice. With a raw egg yolk it becomes a variation of Tamago Kake Gohan. On cold noodles such as Zaru Soba, you eat natto with dipping sauce and radish. A spoonful of natto in miso soup is called natto-jiru in Japan. Chopped, it goes well with kimchi or in a Tamagoyaki.
