Natto

A sticky soybean food

Natto is a Japanese fermented soybean food. Whole soybeans are steamed and then inoculated with a natto starter, and the warm incubation turns them into a sticky, stringy mass with a strong smell. It is eaten on rice, often with soy sauce, mustard and green onion, and it is also used in rolls and soup, as Kikkoman's account describes.

The starter is the key to the batch. Commercial natto is made from Bacillus subtilis cultures selected for the job, and research on natto-associated strains reports differences among tested strains. A home batch that uses a retail pack or a liquid starter does not always disclose the strain, so the culture cannot be identified from the product name alone.

A home batch with a warm hold

The most complete batch comes from a home video that uses 250 g of dry soybeans. The beans are soaked for about 15 hours, then pressure-steamed with 1.5 cups of water for 40 minutes. Once the heat is off, the cooker rests for 15 to 20 minutes before it is opened.

Frozen retail natto is cut into nine portions. One portion is mixed with a teaspoon of cooled soybean cooking liquid and combined with the beans. The beans go into a shallow heat-safe dish under two layers of film, one with air holes, and a towel. An oven light and a hot-water bottle keep them warm. The creator aims for 35 to 40°C and reports readings between 38 and 41.5°C over about 20 hours, while the caption says 18 to 22 hours. The wording of where the starter is mixed is not fully clear in the captions.

Other home batches

A video from the Netherlands uses 400 g of dry soybeans, a 12-hour soak, a 1 hour 45 minute boil, one quarter of a frozen retail pack, and a 42°C yogurt-maker incubation for 24 hours, followed by one and a half to two days in the refrigerator. A liquid-starter video uses 150 g of beans with 1 g of liquid starter, pressure-cooks them, and holds them in a foam box warmed by hot water for 20 to 24 hours. A yogurt-maker video uses 150 g of beans and half a retail pack, steams for 30 minutes, incubates at 45°C for 24 hours, then refrigerates for 24 hours and reports about 300 g of finished natto.

The batches differ in starter, mass and temperature, and none of them is a standard. This page keeps each one as the creator's account and does not merge them. One video compares four container layouts; its captions are too garbled to pair the observations with each layout, and the creator's preference for a paper-towel layer is a personal choice, not a safety finding.

Temperature, cold holding and limits

The reviewed batches hold the beans warm for about a day and then refrigerate them. The BC Centre for Disease Control's guidance on natto is general safety context. It does not validate these home temperatures or the creator's one-week storage claims.

Surface film, aroma and stickiness are the creators' observations. They are not measurements, and they do not show that a batch is safe to eat. The sources do not establish an earliest food attestation or a batch location for the home methods.

The BC Centre for Disease Control's Natto guidance identifies Bacillus cereus and Clostridium perfringens as hazards when soybeans are improperly cooked or cooled. It specifies soaking in potable water at 4°C or below, controlling the period after cooking so starter is added within two hours after the beans fall below 60°C, and cooling fermented soybeans to 10°C or below within four hours. The home videos do not report the soak temperature or timed cooling controls. These professional guidance points are separate safety context; they do not validate the video batches or turn them into a tested home process.