You are going to collect Lactobacillus from the air around you.
Add 1/2 cup of uncooked rice to 1 cup cool water in a bowl and stir. The water will become cloudy with rice starch.
Pour just the rice wash into a 1 quart mason jar or similar
Place the open mouth jar (no lid) within 2 feet of the floor for a couple days. I might leave on my back porch step for an afternoon, etc. Were just collecting microbes at this point. The air will deliver them.
After 2 days, loosely place a lid on mason jar. Keep in room temp dark place for two more days.
After two days there will be a stinky film on the top. This is perfect. You have all sorts of wild bacteria, fungus, and yeasts. Be we only want a certain type of bacteria, Lactobacillus.
We selectively feed Lacto B the lactose in milk. The rest of the organisms in that rice wash dont do so well in that environment, and Lacto B dominates.
So we have 2 cups of room temp milk. Skim, whole, 2%, whatever. Not hot and not cold. 70F is great. To that milk, add just a teaspoon or so of that stinky rice wash. Throw away the rest of the rice wash.
Two days later, the Lacto B will have separated much of the protein from the yellow whey (serum). Scoop out the cheese-like protein so you can get at that yellow serum. Animals love that protein, BTW.
Mix the yellow serum 1:1 with molasses, and 20 parts water. Its ready to store in the fridge. The molasses will also feed the Lacto B.
This is still concentrated. You can add a couple tablespoons of this to a gallon of water for soil or foliar. You can add this to soil to start the microbes after a new soil mix. You can spray as a foliar in veg or early flower.