After crushing and pressing the grapes, the grapes go into the fermentation tank. During this process the grape juice turns into an alcoholic beverage. Fermentation is the process where the sugar transform into ethanol and carbon dioxide as a by-product. The biggest percentage of energy usage goes to the fermentation process, because of the importance of the temperature and speed of the fermentation. The temperature for white wine should be between 18 and 20 °C and for red wine 29°C. The level of oxygen present in the must at the start of the fermentation is also an important consideration. During fermentation several wine faults can take place. Primary fermentation takes 5 to 14 days and secondary fermentation takes 5 to 10 days. Different types of tanks are used for fermentation, stainless steel tanks, open wooden vat, inside a wine barrel or inside the bottle itself.