Fermentation can be carried out using a number of methods; among these are: batch, continuous, and membrane recycle fermentation. Batch fermentation is the more simplistic approach and has been in practice for a number of years. The overall process of producing ethanol involves the following steps: milling, cooking, fermentation, and distillation. Removal of the ethanol is the key function of the distillation; other byproducts will be removed in this step because of the difference in boiling points. Milling and cooking are basically pretreating steps that facilitate a proper condition for fermentation; the milling step essentially breaks down the sugar containing feed to very small particles, and the cooking step allows for the yeasts to reach the proper reaction temperature to start actual fermentation.