Cider Science

• Fermentation occurs when microscopic organisms called yeast are introduced to a liquid that contains sugars for them to feed on. The yeast consume the sugar and create alcohol and carbon dioxide as byproducts. Once the alcohol level in the mixture has risen to a high enough level, fermentation stops. The first alcoholic beverages may have been created when attempts to store fruit or grain were accidentally contaminated by yeast.

Modern Cider-Making

• Controlling the fermentation process is the basis of making cider. Ingredients are added to the juice to help nourish the yeast and sustain the fermentation process. From there, the juice is filtered to remove impurities. The cider-maker then seals the apple juice in a container with an airlock. The airlock allows carbon dioxide to escape but prevents air from entering. "Racking" involves transferring the cider to a series of new containers, leaving behind more residue each time until the cider is ready to bottle.

Pasteurization and Fermentation

• Although early cider was probably created by wild yeast occurring naturally on apples, modern cider-makers prefer to control the process by using a controlled amount of winemaking or brewing yeast. Some potential cider-makers may be concerned that pasteurization will have killed off the natural yeast in the apple juice -- but, in fact, most cider-makers working with unpasteurized apple juice kill off the natural yeast anyway using sodium metabisulphite.

Chemical Preservatives

• Some cider experts warn that chemical preservatives in processed apple juice can harm the fermentation process. Although pasteurization, once over, will have no further effects, chemical preservatives may kill the yeast introduced into apple juice to make it ferment. If you intend to use store-bought apple juice to make cider, make sure that it does not contain chemical preservatives such as sodium benzoate or potassium sorbate.