Fermentation is the process by which alcoholic beverages and some biofuels are produced. To start fermentation you need two main things: sugar and micro-organisms. In this case we are going to take glucose as our sugar and yeast as the micro-organism. When something is fermented the yeast turns the sugar into alcohol (ethanol) while also giving off carbon dioxide and energy. This can be represented by a word equation:

 This process is carried out under anaerobic conditions – i.e. without oxygen. The yeast is not the brightest bulb in the box as it eventually kills itself. Ethanol is a poison and once it reaches a certain concentration it kills the yeast.