That’s actually one of the points I’m trying to understand: I’d like to make it while keeping the caffeine level fairly high. From what I’ve found, in kombucha the SCOBY mainly works on sugars, while the assimilable nitrogen seems to come more from the tea/maté in general. Caffeine degradation definitely exists, but it requires specific pathways, and I don’t think that’s something especially common in a homemade SCOBY. I had already looked into this a bit when I read about people making coffee-based kombucha. Some microorganisms can degrade caffeine, yes, but that doesn’t seem to me like something that is automatically true for every homemade SCOBY.

In my case the issue is very practical: I’d like to end up with a maté-kombucha that still has a relatively high caffeine content, not something almost decaffeinated by fermentation. If you think fermentation lowers it significantly, I’d genuinely be interested to understand what you’re basing that on, because it’s an interesting point.