Very good question!
I am not an expert, but my understanding is that they use a special, low sugar yeast found on a number of worlds, including those in the Denubian localverse. However, unlike Choco-Coffee(TM) it’s not exclusive to the Denubians so Hesseforthalus doesn’t have a lock on the distribution rights.
This is one of the things that makes him such a powerful figure in the Abyss (as even Sam notes in Book IV). You cross him and you get cut off from the Choco-Coffee(TM).
Anyway, they use this yeast, I’d be tempted to call it D’Yeast, but that’s not really true, it’s from the material plane. Along with some of the ingredients of X-Glargh (although in smaller proportions) and then a boatload of magic. This is necessary to keep the remaining animus in the cells and to prevent/repair cellular damage during the ice distillation process (as with ice wine)
I’ve never tried to make any myself. I’m fine with x-glargh if I were to get thirsty, but in general, I’m a pipe man myself. And cookies, brownies, and anything made with D’Butter.
Tizzy