[sjmulder]

The explanation as to why flour yeast and grape wine yeast are unsuitable is a bit of a tautology. I know little about yeast. Can someone explain why one sort of yeast is not suitable for another use? And why is "sorghum, the traditional fermenting agent of banana wine" unsuitable or not acceptable to regulators?

[jrflowers]

Different yeasts have different temperature and alcohol tolerance. For example a bread yeast may not continue making alcohol beyond 5-6%, or another yeast may only be productive in a narrow temperature range that’s too warm or too cool for a given application.

[amonon]

To add on, different yeasts also vary in their ability to metabolize carbohydrates. In general, a wine yeast will be less able to metabolize complicated carbohydrates than a beer yeast. Beer yeast tends to be more sensitive than wine to alcohol levels. More importantly, it's possible Rwanda lacks any serious brewer's yeast industry that is suitable. Kveik may be able to ferment at both 37C and up to 16% ABV but that's definitely an unusual trait in a yeast and I would not be surprised if they resulting wine was... funky.

[dluan]

It's similar to the malting process. Certain ingredients will contain enzymes and other important metabolites that can break down complex sugars into smaller simpler sugars that can be eaten by yeast (glucose, fructose). You need them to get a fermentation started and warmed up.

[stubish]

Even more confusing: "We mixed the fermenting agent with sorghum flour to keep the traditional color and aroma of sorghum, the traditional fermenting agent of banana wine"

So they developed a yeast to replace the sorghum as the fermenting agent, and then mix sorghum in. What has been gained? Does yeast make for a more controlled fermentation making regulation easier? Or just easier to industrialize?

I suspect that using sorghum for fermentation really means using whatever wild yeast happened to be on the sorghum, and the results too variable to regulate for commercial sale or export.

[dmurray]

> I suspect that using sorghum for fermentation really means using whatever wild yeast happened to be on the sorghum, and the results too variable to regulate for commercial sale or export.

Definitely this. Sorghum is not a "fermenting agent": it's not an organism that eats sugars and shits out alcohol and carbon dioxide (actually, it's pretty much the opposite). It's just somewhere wild yeast likes to live.

[yial]

Sorghum is acceptable I believe. It’s the fifth most produced crop in the world. It sounds like what might not have been acceptable is using wild yeasts to ferment it.