For thousands of years, humans have been processing fruit to enjoy its benefits all year round—and apples are no exception. When apple juice is left untreated, various natural processes begin to unfold. Among them, one usually takes the lead: alcoholic fermentation.
Alcoholic Fermentation – The Path to Apple Wine
Apples and their juice naturally contain yeast, which thrives in freshly pressed apple juice under autumn conditions—rich in sugar, with the right pH and an ideal temperature (around 15°C). In this process, yeast converts sugar into energy, producing alcohol and carbon dioxide along with numerous other metabolites. This is how apple juice naturally transforms into apple wine.
To ensure that only alcoholic fermentation dominates in the must, we must limit oxygen exposure, as it promotes other (undesirable) processes. That’s why an airlock is used during fermentation, allowing the process to occur in anaerobic conditions.
What Happens After Alcoholic Fermentation?
Once the yeast has consumed all (or nearly all) the sugar and apple wine has reached a sufficient alcohol level, alcoholic fermentation comes to an end. However, this does not mean that all microbiological activity has stopped.
Under the right conditions, malolactic fermentation (biological deacidification) can occur, driven by lactic acid bacteria naturally present in fruit wines. This process does not change the fact that it is still a fruit wine, but it can significantly impact its sensory characteristics—flavor, aroma, and texture.
From Apple Wine to Apple Cider Vinegar – Acetic Acid Fermentation
If apple wine is left untreated and exposed to air, acetic acid fermentation (oxidative fermentation) begins. Acetic acid bacteria convert alcohol into acetic acid in the presence of oxygen, producing other secondary metabolites in the process. The optimal temperature for this transformation is slightly higher than for alcoholic fermentation—around 28°C.
It is important to note that acetic acid bacteria do not use oxygen directly from the air but require dissolved oxygen. If apple wine is not protected from oxidation, it will naturally turn into apple cider vinegar over time.
Controlling Fermentation to Improve Quality
This is the natural journey of apple juice: it first ferments into apple wine and can later develop into apple cider vinegar. These processes have been known and used for millennia, but modern fermentation science allows us to control them more effectively.
To achieve the best quality and avoid unwanted byproducts, we must understand the conditions that influence fermentation. This way, we can prevent apple wine from unexpectedly turning into vinegar—nature follows its course, but with knowledge, we can guide the process in the desired direction.
A Challenge for You: Try Fermenting!
Experiment with cultivating yeast and acetic acid bacteria to find the ideal conditions for your perfect fermented product. One tip: if you want to make apple cider vinegar, start with freshly pressed apple juice or naturally fermented wine. If you try using stabilized, sulfited wine, the result may disappoint you—rather than clean acetic acid, you might get an unpleasant "off" taste.
Ready to take on the challenge?
