Lukewarm Releases Umami

It's technical and precise but the process is simple to follow.

Another point is that the enzymes that break down the ribonucleotides into guanylate work most effectively at a temperature of between 30 and 40ºC, and when subjected to high temperature they become inactive. Thus if the dried shiitake is soaked in boiling water, the enzymes are inactivated and no more guanylate can be released. By contrast, if the shiitake is soaked in lukewarm water around 30-40ºC, then the enzymes can continue to produce guanylate from ribonucleotides, increasing the umami taste.
Advice from Dashi and Umami: The heart of Japanese cuisine

And so for day 983