The Secrets of Grape Fermentation: Do Grapes Ferment Naturally or Do You Need to Add Yeast?

Have you ever wondered whether grapes ferment naturally or if some additives are required to produce alcoholic beverages? The answer to this question lies deep within the mysteries of wine-making. From traditional methods to modern winemaking techniques, the process can vary significantly. This article explores the natural fermentation process and the roles of wild and proprietary yeasts in grape fermentation.

Understanding Natural Grape Fermentation

When grapes are harvested, they naturally contain a protective layer called bloom on their surface. This bloom is home to wild yeasts, which can begin to ferment the grape juice naturally. This process, known as carbonic maceration, is utilized in certain types of wine production, such as Beaujolais wines. During carbonic maceration, entire grapes are kept in an oxygen-free environment, where the yeast feeds on the sugars within the berries, producing alcohol and carbon dioxide.

However, in most cases, wild yeasts are not the ideal choice for fermentation due to their sensitivity to alcohol and their ability to produce off-flavors. In the past, before the understanding of yeast by figures like Louis Pasteur, many wines suffered from poor quality as wild yeasts competed with proprietary wine yeasts for dominance during fermentation. This often led to wines with off-flavors and incomplete fermentation.

Modern Winemaking and Proprietary Yeasts

Today, modern winemaking practices involve the deliberate addition of specific yeasts to ensure a clean and controlled fermentation process. Proprietary yeasts are chosen for their ability to resist alcohol, increase alcohol content, and produce better-tasting wines. By adding commercial yeasts, winemakers can significantly reduce the risk of producing off-flavored wines.

The Role of Wild Yeasts in Grape Fermentation

While wild yeasts can initiate fermentation, they often pose several challenges. Firstly, they may stop fermenting before all the sugar is converted, resulting in low alcohol content and a sweet wine that might or might not be desirable. Secondly, wild yeasts may disperse during fermentation and not settle properly, leading to a cloudy wine. Finally, wild yeasts cannot be controlled in terms of quality, and some can produce unpleasant flavors and odors.

To mitigate these issues, winemakers often take proactive measures. For instance, crushing the grapes with a Camden tablet or adding 5g of metabisulphite powder per gallon of grapes can serve to kill off unwanted wild yeasts. After 24 hours, the SO? will dissipate, and proprietary wine yeast can then be introduced to ensure a high-quality and consistent fermentation process.

Conclusion

While grapes can ferment naturally, the presence of wild yeasts is not always beneficial. The optimal approach to grape fermentation involves a combination of understanding natural processes and employing controlled, proprietary yeasts to achieve the best results. By carefully managing fermentation and using appropriate yeasts, winemakers can produce wines with consistent quality and superior taste.