When the solids have been removed, fermentations are cleaner and better controlled. Juice is often settled over night and then the clear juice is racked off the sediment the next day. The juice must be kept cold, and the proper amount of sulfur dioxide should be used. Sometimes, additional clear juice can be obtained by resettling the residue. Sulfur dioxide is used to arrest yeast activity, but reasonable quantities of SO2 will not kill the native yeast.
Most winemakers prefer to add pure cultured yeast to start fermentation.
Cultured Yeast Most home winemakers prefer dry yeast because using it is easier. Some yeasts like Epernay does not tolerate high levels of alcohol. Steinberg yeast does not tolerate high levels of sulfur dioxide. Montrachet yeast should never be used with grapes containing residual sulfur dust. Pasteur Champagne yeast can produce large amounts of foam in warm fermentation.