Cider apple
Cider is made in several countries and can be made from any apples. Historically the flavours preferred and varieties used to produce cider have varied by region. Many of the most traditional apple varieties used for ciders come from or are derived from those from Devon, Somerset and Herefordshire in England, Normandy in France, and Asturias in Spain, and these areas are considered to have their own broad cider styles although the many exceptions make this more of a historic footnote. Normandy cider is usually naturally carbonated and clear: Asturian cider apple varieties are mainly 'sharps' or mild 'bittersweets', producing a mildly acidic cider which is customarily served by being poured from height into the glass to oxygenate it.
Cider
An important component in cider-making is the addition of sulphur dioxide to inhibit the growth of many spoilage bacteria or yeasts in the juice. This encourages the inoculated yeast to dominate the juice environment, converting sugars to alcohol. Once sulfur dioxide dissolves in the juice, it converts into a pH dependent mixture of bisulfite, sulfite ions, and molecular sulfur dioxide. The "unbound" sulfur dioxide provides the antimicrobial environment in the juice, while the bisulfite and sulfite ions contribute to flavor. The quantity of sulfur dioxide needed to inhibit microbial activity is directed related to pH of the juice; lower pH means less should be added, while higher pH juice requires more. Many cider producers add sulfur dioxide immediately after pressing and juicing, but before fermentation. However, in some cases it can be added afterwards to act as an antioxidant or stabilizer. This prevents the finished cider from releasing hydrogen peroxide or aldehydes that produce "off" odors and flavors.