Why is Sake / Shochu used to make Mirin ? Can we add yeast to the Koji-Rice mixture instead ?
Finished Sake isn't used to make the mirin. But a scoby is. Like sake, mirin needs the bacteria in the scoby to make the sugars for the yeast.
So just adding yeast to the rice will not work. You need something for saccrification process (enzymes from bacteria or fungi) to convert the starch to sugar.
Edit: based on Pete and neels comments, if your koji-rice mixture has converted the starches to sugars then yes adding yeast will work by making a scoby.
1Koji-rice is treated with Aspergillus oryzae which secrets a amylase enzyme that converts the starch to lesser dextrins and fermentable sugars. It is used for fermentation and as a sweetener (maybe like malt is). Nov 20, 2017 at 17:02
1@EvilZymurgist But Koji-rice is used to make Amazake, which is basically starch converted into sugar... en.wikipedia.org/wiki/Amazake– NeelNov 21, 2017 at 8:21
Can the yeast can use the sugar so produced via fermentation? Nov 21, 2017 at 13:19
@GrainMother if there are sugars it will ferment. Nov 21, 2017 at 15:06