Fermentation is the reaction that is used to produce alcohol from sugar. It is an anaerobic reaction, which means it requires no oxygen to be present other than the oxygen atoms contained in the sugar. Consequently, fermentation is conducted in a sealed, air-tight container. The other ingredient required for the reaction to take place is yeast.
Glucose is a sugar molecule and is the main component of starch, cellulose and glycogen. It is named after the Greek word ‘glycos’ meaning ‘sugar or ‘sweet’ and was first derived from raisins by the scientist Andreas Marggraf in 1747. Glucose contains the six carbon atoms, 12 hydrogen atoms and six oxygen atoms required to make alcohol. The structure of glucose is thought of as constantly switching between a chain and a ring because the carbon bonds of the chain are flexible enough join together to form a chain ring, but easily rebroken.
Yeast is not a chemical but a living microorganism. It is useful to the fermentation process because it helps the glucose molecule break down into its constituent parts, which then form alcohol. It is the enzymes contained in the yeast, rather than the yeast itself, that breaks the chemical bonds of the glucose and allows the formation of alcohol. Because of this, the yeast remains unchanged at the end of the reaction while the glucose molecule is deconstructed. Substances that aid a reaction but remain unchanged afterwards are known as catalysts.
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After the glucose has been broken down, its constituent elements form ethanol and carbon dioxide. The chemical formula of ethanol is C2H5OH, and it is the ‘OH’ on the end of the formula that marks this chemical as an alcohol. Alcohols are actually a large group of chemicals, including methanol and pentanol, but it is ethanol that is used to create the alcohol found in beers and wines and other beverages. The other elements from glucose also join together to form carbon dioxide, which is given off as a gas.
During the fermentation reaction, it is vital that oxygen does not enter the reaction chamber. The addition of oxygen to the reaction will lead to the creation of ethanoic acid rather than ethanol, which is the main aim of conducting the reaction in the first place. Ethanoic acid is what gives ‘off’ wine its vinegary taste and will completely ruin your batch of alcohol. This is why fermentation tanks are kept sealed during the reaction.