There are many ways to develop and maintain mixed cultures of yeast and bacteria. For the purposes of this discussion, we’ll focus on three types of cultures as we define them. This terminology isn’t intended to be definitive, but it’s useful to explain what we mean when we use shorthand terms.
Native Cultures
In wine- and cider-making, a native fermentation is one that occurs without pitching a culture. In any fermentation, it’s possible for fermenters to come from ambient sources or contamination from equipment, such as barrels, tanks, or presses. Generally, a native fermentation is believed to occur due to yeast and other cultures that reside on the skin of the fruit. It is common for native grape cultures to contain Oenococcus or other malolactic bacteria, and I’ve had success using native grape cultures that contained Brettanomyces. Native cultures also can be gathered from flowers, but in my experience, this is a more esoteric pursuit. My suggestion for those who pursue it is to use very low-gravity wort with proper acidification and no hopping.
Wild Cultures
While many lab scientists will refer to “wild” Saccharomyces strains, our use of the term in a brewing context is solely to describe cultures taken from a coolship or similar ambient inoculation. While most coolship inoculations take place in existing breweries where the culture inside the building is largely what’s captured, it is possible to capture and propagate fermenters from the air in places where there is no history of fermentation.