The Different Yeast Types used to Ferment Wine Grape Must
Probably the best argument for adding cultured yeast is that natural yeast is not extremely effective at high sugar levels and can die before the desired alcohol level is reached. Cultured yeasts have been specifically developed to not be as susceptible to these problems. Different strains have varying responses to these two issues.
An additional potential problem to using natural yeasts is that there are often adverse bacteria on grape skins. In some circumstances, this can be disastrous to the winemaking process. However, be aware that some of California’s best wines have and continue to be fermented with natural yeast.
Natural yeasts can be neutralized by adding sulfur dioxide to the juice before fermentation. Montrachet and Champagne are two cultured yeast types that are commonly used during winemaking.
Very few strains of yeast can survive over 16% alcohol. Yeast is only active between 26 and 97 degrees Fahrenheit. The enzymes responsible for fermentation are denatured above 149 degrees Fahrenheit. Many high-quality wines are flash pasteurized at 176 degrees Fahrenheit for about 1 minute.
Sulfur dioxide or sorbic acid is added after fermentation to kill any additional yeast cells. Pressure over 8 atmospheres will also kill yeast cells.
There are 2 major types of yeast used in the winemaking process: natural and cultured. Natural yeasts are present on the skins of grapes. They stick to the slightly waxy coating that develops on grapes. The yeast cells and other natural organisms that live on a grape’s skin are called the “bloom.”
Cultured yeasts are raised in the laboratory to develop certain characteristics. Many winemakers prefer cultured yeasts for their reliability and predicable behavior during the winemaking process. Although the addition of sulfur should be kept to a minimum, it is very difficult to make a stable wine without using sulfur at all. Too much sulfur will create off-aromas and can ruin a wine.
Yeasts are tiny fungi organisms used in the fermentation process of wine. There are thousands of species of yeasts, but Saccharomyces cerevisiae is most commonly used for wine production. In nature, yeasts often thrive in environments that contain a lot of sugar. Yeasts are naturally present of grape skins as well as many other fruits.
There are benefits of using either natural occurring or added cultured yeasts. The addition of one instead of the other depends on the winemaker’s philosophy.
Many believe that natural yeast imparts more complex flavors and aromas in resulting wines. Others culture specific yeasts to give their wines what they believe to be more controlled and predictable characteristics. In modern winemaking, the latter type of yeast is more commonly used.
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