Natto in a sous vide bath

Mise en place — set out in the order it goes in

1. 

   Soybeans300 g dry, rinsedStep 1

2. 

   Spores1 scoop in 1 tbsp boiled waterStep 3

3. 

   To serve

   • soy
   • karashi
   • scallion

   Step 7

Prep order — what happens when, and what overlaps

Start the soak the evening before. The natto is first eaten on the third evening.

Step by step

1. 

   1Soak overnight

   12–18 h

   For this step

   • Dry soybeans300 g
   • Waterfor soaking and steaming

   • Rinse the soybeans, then cover them with three times their volume of cold water.
   • Soak 12–18 hours. They roughly double, and a bean splits cleanly into two flat halves with no dry core.

   

2. 

   2Steam until very soft

   high40 min – 5 h

   • Drain. Pressure cooker: beans on the steamer rack over about 2 cm of water, 40 minutes at high pressure, then let the pressure drop on its own.
   • No pressure cooker: simmer them in plenty of water for 3–5 hours, topping up so they stay covered.
   • Test one: it should crush with almost no effort between your thumb and ring finger, like a cooked chestnut. Firmer beans make weak, dry natto.

   

3. 

   3Spores in while hot

   5 min

   For this step

   • Natto spore powder1 packet scoop (see packet)
   • Boiled water1 tbsp

   • Meanwhile, scald the glass dish, a spoon and the tubs with boiling water. Natto bacteria crowd out most other microbes, but give them a clean start.
   • Stir one scoop of spore powder into 1 tbsp of just-boiled water. Nattomoto's tiny scoop (0.1 g) is enough for up to 1 kg of dry beans, so one scoop is plenty here. Follow your packet if it says otherwise.
   • Drain the beans well and, while they are still steaming hot, pour the spore water over and fold gently until every bean is coated. The spores survive the heat; the other microbes don't.

   

4. 

   4Spread out and cover with holes

   5 min

   • Spread the beans in the dish in an even layer no more than 2 cm deep. A deeper layer goes hot and smelly in the middle.
   • Lay cling film straight onto the beans and poke 10–15 holes through it with a skewer. The bacteria need air; the film stops the top drying out.
   • Lay a loose sheet of foil over the dish so condensation from the bath lid can't drip in.

   

5. 

   

   

   5Hold at 38–41°C in the sous vide bath

   22–24 h

   • Stand two heavy upturned glasses in the bath and fill it to just below the top of the glasses, above the circulator's minimum line. Set the circulator to 41°C.
   • Set the dish on the glasses. The water may touch its base but must stay well below the rim, and it must not lean on the circulator.
   • Cover the whole bath with its lid or cling film, so the air above the water stays warm and damp.
   • After an hour, push the probe thermometer through the film into the middle of the beans. Aim for 38–41°C. If it's lower, raise the bath a degree or two, or add water so more of the dish sits in it.
   • Leave it 22–24 hours. Check the water level once and top up with warm water.

   

6. 

   6Check for strings

   2 min

   • Lift the foil and film. The beans should have a thin white bloom and look a little darker. They smell earthy, a bit like ammonia.
   • Stir a few with a chopstick. Fine, sticky strings should follow it.
   • No strings yet? Cover and give it a few more hours. Pink, black or fuzzy coloured mould, or a rotten smell, means throw it all out.

   

7. 

   7Cool, ripen, portion

   24 h

   For this step

   • Soy sauce or the natto tare1 tsp
   • Karashi mustarda dab
   • Scallion1 tbsp

   • Let the dish cool to room temperature, covered, about an hour.
   • Fridge it for at least 24 hours. The ammonia fades and the strings get longer and stickier.
   • Pack into 50 g tubs. Fridge up to a week, freezer up to two months; thaw overnight in the fridge.
   • To eat: stir a portion hard with chopsticks 30–50 times until it's white and frothy with strings, add the soy and karashi, stir again, and pile it on hot rice with the scallion.