Yeast is a fascinating microorganism that plays a crucial role in winemaking. Specifically, the yeast species Saccharomyces cerevisiae is the primary yeast used in wine fermentation. As a sommelier and brewer, I have had the opportunity to work with various yeast strains, but S. cerevisiae is by far the most common and important one in the world of winemaking.
This microscopic fungus is responsible for converting the natural sugars present in grapes into alcohol through the process of fermentation. It consumes the sugars and produces ethanol as well as carbon dioxide as byproducts. These chemical reactions give wine its characteristic alcoholic content and effervescence.
The role of yeast in winemaking begins during the crushing and pressing of the grapes. As the grapes are broken open, the natural sugars are exposed, providing a food source for the yeast. The yeast then begins to consume these sugars, converting them into alcohol and releasing carbon dioxide as a result. This process typically takes place in large fermentation vessels, such as stainless steel tanks or oak barrels.
During fermentation, the yeast cells multiply rapidly, creating a thick layer known as the “lees” or “sediment.” This sediment consists of spent yeast cells, grape solids, and other particles that have settled to the bottom of the fermentation vessel. The presence of lees can contribute to the flavors and aromas of the final wine, as well as add complexity and texture.
After fermentation is complete, winemakers have the option to remove the yeast sediment through a process called racking. This involves transferring the wine to a clean vessel, leaving the sediment behind. Alternatively, winemakers may choose to leave the wine in contact with the lees for an extended period, a technique known as “sur lie” aging. This can impart additional flavors and textures to the wine, resulting in a more complex and nuanced final product.
While Saccharomyces cerevisiae is the dominant yeast species in winemaking, it's worth noting that other yeast species and strains can also be present. These can come from the grapes themselves, the winery environment, or be deliberately added by the winemaker. Different yeast strains can contribute specific characteristics to the wine, such as aroma profiles, fermentation speed, and tolerance to alcohol levels.
In my experience as a sommelier and brewer, I have witnessed the significant impact that yeast selection can have on the final wine. The choice of yeast strain can greatly influence the aromas, flavors, and overall style of the wine. For example, certain yeast strains may enhance fruity or floral characteristics, while others may emphasize earthy or spicy notes. The skill of the winemaker lies in selecting the right yeast strain to complement the grape variety and desired wine style.
Yeast, particularly Saccharomyces cerevisiae, is the key microorganism responsible for transforming grape sugar into alcohol during winemaking. Its role is fundamental in creating the unique flavors, aromas, and textures that we associate with wine. The choice of yeast strain is a crucial decision for winemakers, as it can greatly influence the character and quality of the finished product.