miayo's Profile

Here's what I learned from Japanese resources;

It's the different level of maillard reaction (never heard of it!), or browning reaction, that decides Red or White, for which the length of aging is the major factor. The method of cooking soy beans (red:steam, white:boil) or the type and quantity of Koji (the fermenting agent), etc also matter.
Red: longer aging (over 1 yr), more brown, salty and rich. White: shorter aging (a few months), sweet and light. Yellow in between.
Black, yea just soy beans and the way they use Koji is different. About 2 years of aging.

Yes, it is common understanding in Japan never bring the soup to boil after adding miso to keep the aroma and the tender taste of miso. Some noodle(Udon) recipes often with Black miso prefer simmering though.

To put miso into the soup, it is also popular to use a tool like this http://www.amazon.co.jp/dp/B0001BDD20 It goes directly into the soup in the pan. Otherwise you just keep the miso in a ladle until it becomes completely creamy while mixing with soup and releasing it little by little.

Now I learned a lot about Miso myself. Thank you!