I've been reading for some time and have to say many of you have been a big inspiration, so thanks!
I'm interested in Koji more so than Sake itself, because one of my goals is to use the enzymes to make alcoholic beverages from other types of starch. I like to experiment. I've done a fair amount of searching and reading, and have the privilege of a university student ID to access peer-reviewed articles related to sake, yeast, koji, and other brewing-related things.
A couple months back I found this amazing reference to anything koji-related, a free online book called "The History of Koji":
On the forum here, it looks like Claes Nilsson briefly mentioned this book after posting a website link about the history of industrialization of sake. I wanted to make a special post for this because I've found this book to be hands down the best resource on the topic. It is a massive annotated bibliography on everything related to koji, including sake, in chronological order.
Some of you may have glanced at this already and been turned off because a lot of it is purely historical, briefly summarized information, or pertains to other koji-related things such as miso or soy sauce. I have to say that I also felt that way at first. However, after using the search function a few times, with keywords such as "wood ash", or "Takamine", I started to feel strongly that this is an important resource. From this book I found the original Takamine patents on his methods of growing koji, including references to nutritional supplements and different growth mediums. I found the free online book titled "The Chemistry of Sake Brewing" by R.W. Atkinson in 1881, an indispensable part of any sake library.
A lot of the references are very hard to find on the internet, being either very old articles, or being kept behind a paywall. However, I've realized after using my student ID to access a few articles that the summaries in this book are usually more than sufficient.
Anyway, I'm sure some of you have found this book already and are way ahead of me, but I wanted to make this special post so that newcomers could find it, as I was only able to find one vague reference on this forum.