Hi, I saw this Koji sourdough starter instruction: https://youtu.be/sEUokdUqE2M which makes the starter in several steps. First, a mixture of raw rice and cooked rice (along with koji and water) is used. But starting from the second step, only cooked rice (along with koji, water, and previous batch) is used.
I wonder why this Koji sourdough starter is being fed with cooked rice instead of raw rice powder, which I would think is more of the equivalent of raw flour (which is what typical sourdough starter uses)? What does it do differently than raw rice flour? I think part of it is to feed the koji mold... what does it do to yeast? Does it speed up yeast production and minimize lactobacillus? Finally, can we replicate this method with cooked wheat (flour) to make an "alternative" sourdough starter?
Others with more knowledge may chime in, but having brewed quite a bit of sake, and made koji rice in the process, cooking gelatinizes the starch in rice, causing it it to take up moisture and thus be made available to the A. oryzae mold.
Interesting topic; I look forward to the discussion, thanks for the thread.
Plants store their carbohydrate reserves in tightly packed granules. With wheat flour we rely on milling to break some of these granules open and this damaged starch accounts for roughly 4-8% of the flour. The actual percentage depends on grain hardness and milling decisions. It is only damaged starch that is available for fermentation.
By cooking the rice all the starch granules are bust open and all the starch becomes available. In doing so, much water is bound up and is why the rice swells. Damaged (free) starch can bind up vastly more water than native (undamaged) starch.
The next step is to utilise Aspergillus mould as a source of amylase enzymes to convert the starch into simple sugars, primarily, maltose. This conversion is called sacchrification.