Place the rice and soaking water in a non-aluminum pressure cooker. Add the sea salt. Bring to a boil and up to pressure. Reduce heat to as low as you can to maintain pressure. You can use a flame tamer if you have one. Cook for 50 minutes. Let the pressure come down naturally or carefully run a little water down the side to help the pressure come down more quickly.

Move the rice to a glass bowl and let sit until it’s just hot to touch. The temperature needs to be less than 140ºF, but still hot enough to activate the koji.

Stir in the koji. Mix well. Spoon the rice and koji into clean mason jars. This amount will fit nicely into two quart jars, but you can use whatever size you have. You can heat the jars first, but I haven’t found this to be necessary. Put a lid on top.

Bring some water to a boil and pour into two more quart size jars. Place all four jars into a medium size cooler. Wrap some towels in there, too, if they fit. Cover. Let sit for a few hours.

After the first few hours, open the cooler to check to make sure the temperature is staying warm. Either shake the jars with rice to mix them a little more or open the jars and give them a stir. The rice should be starting to get a little wetter. Tuck the jars back in. Put more hot water in the other two jars if necessary to maintain the temperature. Cover and let sit.

After about six hours, open one jar of amasake and taste a little to check for sweetness. If you want it sweeter, let it incubate for longer. Add more hot water if necessary. Check every hour until at desired sweetness.

When your amasake is sweet enough, remove from cooler and pour into a stainless steel pot. Bring to a boil and let simmer for a few minutes to kill the koji spores. Let cool.