Winemakers (and brewers) have two options for starting fermentation with yeast: they can use a commercial pure yeast strain with the desired and consistent characteristics, or they can rely on natural fermentation, using what is called the natural flora or wild yeast.
What is wild yeast?
- Wild yeast (also called native yeast, native yeast or natural yeast) enters the winery via the grape surface and adheres to the winery and vineyard equipment.
- Non- Saccharomyces yeasts and Saccharomyces yeasts are two types of wild yeast. The complexity of the grapes during natural fermentation has a significant effect on the organoleptic quality and sensory character of the final wine.
Where does wild yeast come from?
- The nature and quantity of wild yeast are determined by many parameters, including location (that is, soil type, average temperature, rainfall, etc.), grape ripeness and condition, and viticultural technique. The most common yeast varieties identified at the early stage of the natural fermentation of the grape must are non-Saccharomyces yeasts.
- The most important genera include Hanseniaspora, Candida, Pichia and Metschnikowia. The number of non- Saccharomyces species decreases as fermentation proceeds and the wine yeast Saccharomyces cerevisiae completes the fermentation. For example, the ability of non- Saccharomyces to outcompete S. cerevisiae is related to its alcohol tolerance.
Advantages and risks of spontaneous fermentation
Naturally fermented wine differs from pure cultured yeast mainly in its organoleptic appeal, which is why winemakers prefer this fermentation method. Conversely, winemaking with wild yeast is less predictable than conventional fermentation processes. Below are 3 risks:
- Slow or sluggish fermentation: Alcohol tolerance is common in wild yeast. This can lead to sluggish fermentation and undesirably high residual sugar, for example.
- Slower fermentation: Wild yeast present on the grapes is at a significantly lower concentration than inoculated yeast. As a result, fermentation takes longer to start, making the grapes more susceptible to contamination by additional spoilage organisms and oxidation.
- Undesirable by-products produced by wild yeast in the wine can lead to off-flavors
A combination of both processes: sequential fermentation
- Sequential fermentation is a combination of the natural yeast flora and the inoculated cultured yeast.
- The natural fermentation process is allowed to start, and the ongoing fermentation is monitored, for example, by checking the sugar content regularly to determine the current alcohol level. When the alcohol level reaches the appropriate point, a commercial S. cerevisiae strain is added to ensure complete fermentation. In this way, you get the best of both: the richness of wild yeast and a powerful, robust wine.
- The outcome of natural fermentation is very difficult to predict. However, there are techniques to determine whether you want to be "natural" and ferment wine with natural yeast.
- One approach is to identify which yeast species are present on the grapes or in your must. R-Biopharm offers many Real Time PCR kits in this field.
👉 See also the topic Determination of acid content in food by the Enzymatic method
Source: food.r-biopharm.com