Break up the sake lees to fit into a sterilized jar and add the liquid yeast and water that's been boiled and cooled. Adjust the amount of sake lees and water to fit the jar.
The following day, the sake lees should be settled at the bottom of the jar and be forming bubbles.
After 4 or 5 days, the fermentation will slow, and the sake lees will start to float. This is the time to make the sponge dough (bread starter).
Although it may be hard to see, there should be dregs at the bottom of the jar.
(For reference) This is what the dregs in raisin yeast looks like (the white substance are the dregs).
To make sponge dough, sterilize a large jar, a tea strainer, spoon, and chopsticks with boiling water. Strain the liquid yeast into the jar through the tea strainer, pressing it in the strainer with a spoon.
This is the strained mixture! Discard the sake lees left in the tea strainer. Weigh the yeast liquid at this point.
Add the same amount of bread flour as the amount of liquid yeast from Step 7, then mix with chopsticks until it's no longer floury.
Cover the jar with a paper towel, fix it on with a rubber band, then put another rubber band around the jar to mark the height of the mixture, so that you know how much it has risen.
After 3 to 4 hours, it should rise 2 to 3 times in height. Once it rises, close the lid and store it in the refrigerator.
Steps 6 to 10 can be done in one day. After repeating this three times (over 3 days), you will get sponge dough.
On the right is raisin yeast sponge dough. The consistency of the raisin yeast sponge dough is rough and thick. Sake lees yeast makes a finer and more watery sponge dough.
Story Behind this Recipe
I think it's quite hard to measure sake lees yeast, so I hope this is helpful.
It's possible to make fermentation liquid with only sake lees, but it takes a long time and it's difficult, so I recommend using liquid yeast from raisins or the like. The amount of bread flour to make sponge dough (starter dough) is the same as liquid yeast, so, for example, for the first day, use 100 g of both, then 50 g on the second day.