Yeast: sugar into alcohol and gas
Under anaerobic conditions, Saccharomyces converts sugars into ethanol and carbon dioxide, along with trace higher alcohols and esters. The wine-like or bready notes in fermented fruit usually come from this route.
Temperature and aeration are the levers: warmer ferments run faster but produce more fusel alcohols, while excess oxygen pushes sugar toward biomass instead of ethanol.
Lactic acid bacteria: sugar into acid
Lactic acid bacteria produce lactic and acetic acid through homo- or heterofermentation, dropping pH quickly. The acidification itself is a barrier that suppresses many spoilage organisms.
The result is a clean sourness and a rounder mouthfeel — the pathway behind pickles, yoghurt and many fermented vegetable juices.
Mixed fermentation: sequence defines style
Production often combines both: yeast first to build the aromatic frame, then lactic acid bacteria to adjust acidity and texture — or the reverse, dropping pH early to suppress contaminants before aroma development.
Changing the order changes the aroma layering, the acidity curve and the stability of the finished product. It is usually the most time-consuming part of formulation.
Frequently asked
- Does fermented juice contain alcohol?
- Yeast fermentation produces ethanol, though most products end up with very low residual levels or have it removed. The actual figure should come from a certificate of analysis.
- Can both fermentations run at once?
- Yes, as a co-fermentation. Their optimum temperatures and pH ranges differ, so simultaneous operation needs compromise parameters and tighter control.