With many different styles of mead possible, there are many different processes employed, although many producers will use techniques recognizable from wine-making. One such example is to rack the product into a second container, once fermentation slows down significantly. These are known as primary and secondary fermentation, respectively. Some larger commercial fermenters are designed to allow both primary and secondary fermentation to happen inside of the same vessel. Racking is done for two reasons: it lets the mead sit away from the remains of the yeast cells (lees) that have died during the fermentation process. Second, this lets the mead have time to clear. Cloudiness can be caused by either yeast or suspended protein molecules. There is also the possibility that the pectin from any fruit that is used could have set which gives the mead a cloudy look. The cloudiness can be cleared up by either "cold breaking", which is leaving the mead in a cold environment overnight, or using a fining material, such as sparkolloid, bentonite, egg white, or isinglass. If the mead-maker wishes to backsweeten the product (add supplementary sweetener) or prevent it from oxidizing, potassium metabisulfite and potassium sorbate are added. After the mead clears, it is bottled and distributed.