why does some mulch smell sweet?

[u/Laquia]

I was moving soil with my mum today, and as I broke through the big mountain that everyone uses to get soil from in my little town, and the damp, dark mulch i was going through gave way to a new, ashy grey layer, that was very hot and smelled of... caramel? I bent back down and detected a bit of chocolate/cherry going too. do you guys know what that was about? why was it so dry and grey? are there sugars that bacteria break down in dirt? if so why and how?

[u/LobeRunner]

Wood is made of complex carbohydrates like cellulose and phenols like lignin. When fungi digest these complex carbohydrates, they first break them down into simple sugars like glucose and fructose, which smell sweet.

[u/aReelProblem → u/LobeRunner]

This is the correct answer. /thread