Koji amazake

Before you start

You'll need

• Small pot
• Yogurt maker, slow cooker or rice cooker that holds 131–140 °F
• Kitchen probe thermometer
• Clean spoon
• Small jars with lids, for the fridge

Step by step

1. 1

   Heat the water to 140 °F

   Wash your hands, and wash the pot, spoon and appliance with hot, soapy water. Heat 300 ml of water and check it with the thermometer: it needs to reach 140 °F. If it goes over, wait for it to come down before you go on.

   Tip: Hotter doesn't help: at 158 °F the koji's enzymes are lost within a few hours and the amazake comes out barely sweet.

2. 2

   Add the koji and bring it back to 131–140 °F

   Break up 250 g of koji with clean hands, add it to the water and stir well. That's the proportion from a Japanese study: 100 g of koji to 120 ml of water.

   Check it right away: the koji, especially straight from the fridge, cools the mixture below 122 °F. Set it over low heat, stirring constantly, until it's back to 131–140 °F, without going over 140 °F, and move it to the appliance, switched on beforehand so it's already warm. That time below 122 °F counts toward the 2 hours in the rule below.

   Tip: It's also made with extra rice: a well-cooked rice porridge, cooled to 140 °F, with the koji. It comes out thinner and less sweet.

3. 3

   Hold it at 131–140 °F for 6 to 10 hours

   With the mixture in the appliance, take the temperature inside it, not the air: it needs to stay between 131 and 140 °F, and never drop below 122 °F. Check it every hour for the first two hours, then every 2 or 3 hours, stirring each time (our house habit).

   A yogurt maker or a slow cooker that you can set to 131–140 °F works. So does a rice cooker on "keep warm," with the lid ajar and a towel over it: many run hot, so check with the thermometer and open the lid wider if it goes above 140 °F.

   It thickens and gets sweeter as it goes. It's ready when it's very sweet and the grains have broken down: this usually takes 6 to 10 hours; in Japanese commercial kitchens, about 9.

   Tip: Below 122 °F, food poisoning bacteria grow: at 99–104 °F, one study noticed a bacterial smell within 24 hours. If it spent more than 2 hours below 122 °F, adding up every stretch, throw it out (our house rule).

4. 4

   Cool it fast and get it into the fridge within 2 hours

   Divide the amazake among small jars so it cools faster, and put them in the fridge as soon as they stop steaming. Don't leave it out for more than 2 hours.

   Tip: If you want it to stop changing, bring it to a boil before dividing it: the enzymes stop. It doesn't change how long it keeps in the fridge.

5. 5

   Drink it within 3 or 4 days

   In the fridge it separates into layers and thickens: that's normal, just stir it. Drink it cold or hot, as is or with water, or use it as a sweetener. We recommend finishing it within 3 or 4 days, the general rule for leftovers. To keep it longer, freeze it the same day.

How to tell it's going well