In brewing, alcoholic fermentation is the conversion of sugar into carbon dioxide gas (CO2) and ethyl alcohol. This process is carried out by yeast cells using a range of enzymes. This is in fact a complex series of conversions that brings about the conversion of sugar to CO2 and alcohol. Yeast is a member of the fungi family which I like to think of as plants but strictly they are neither plant nor animal. To be specific yeast is a eukaryotic micro-organism. Not all yeasts are suitable for brewing. In brewing we use the sugar fungi form of yeast. These yeast cells gain energy from the conversion of the sugar into carbon dioxide and alcohol. The carbon dioxide by-product bubbles through the liquid and dissipates into the air. In confined spaces the carbon dioxide dissolve in the liquid making it fizzy. The pressure build up caused by C02 production in a confined space can be immense. Certainly enough to cause the explosion of a sealed glass bottle. Alcohol is the other by-product of fermentation. Alcohol remains in the liquid which is great for making an alcoholic beverage but not for the yeast cells, as the yeast dies when the alcohol exceeds its tolerance level.