Yeast is what makes grape juice into wine. They are single-cell organisms (Saccharomyces cerevisiae), which needs food, warmth, and moisture to thrive. Their food is sugar and starch, which they through fermentation convert into alcohol and carbon dioxide.
In wine production you can use yeast developed in a laboratory where you can choose different varieties depending on how you want your wine to taste like. All yeasts have the ability to influence the taste and aroma of a wine in addition to the speed of fermentation, the amount of sulfites produced, and more.
In natural winemaking, one of the key elements is to let the natural occurring yeast in the cellar and on the grapes turn the grape juice into wine. Here the aim is, to let the wine develop as natural as possible, without adding yeast or other compounds which can manipulate the taste.
