It has been difficult to observe and collect Saccharomyces cerevisiae outside areas of human contact, so not much research has been done on its interactions in natural environments. Because it is rarely associated with any other environments other than areas that are close to sites of fermentation, people have wondered whether the yeast could ever be found in the wild. (19). So far, most interactions with its environment have been limited to fermentation. In 1871, Louis Pasteur discovered that grapes had to be crushed in order for fermentation to occur (9). The grape itself has been an ideal habitat for yeast due to its high sugar concentration and low pH, precluding the growth of rival species. (8). Despite this, not many intact grapes contain S. cerevisiae at any one time. In an estimate, only one intact grape berry has the yeast on its surface. (3).
While intact grapes have little to no yeast present on the skin, damaged grapes are more likely to contain the yeast as well as other organisms. Berries were damaged due to the weather, mold infections or birds feeding on the grapes. Additionally, insects may also appear more often if the berry is already damaged. (3) These insects would harbor the yeast in their bodies and deposit them unknowingly while feeding, and the yeast would divide upon exposure to the grape. While it is known that insects harbor microorganisms inside their bodies, it is unknown how yeast is introduced into the insect.