Which fermentation method allows environmental yeast to enter the mash naturally?

The fermentation method that allows environmental yeast to enter the mash naturally is wild fermentation. This process relies on the indigenous yeast and bacteria present in the environment, such as on the grains, in the air, and on fermentation vessels. This creates a unique and often unpredictable fermentation profile, as the specific strains of yeast can vary widely depending on the geographical location and conditions.

Wild fermentation is particularly valued for the complexity and unique flavors it can impart to the finished product, making it different from traditional methods that might use cultivated or isolated yeast strains. This technique is often embraced by craft distilleries and winemakers who want to capture the essence of their local terroir, enhancing the character of the bourbon.

In contrast, controlled fermentation involves using a specific yeast strain that is selected for its desirable qualities, while spontaneous fermentation can refer to initiating fermentation without additional yeast but might not necessarily rely on wild environmental yeasts exclusively. Hybrid fermentation combines both wild and cultured yeasts to achieve a balance, but it still does not emphasize the natural entry of environmental yeast to the same degree as wild fermentation does.