Cider apples are a group of apple cultivars grown for their use in the production of cider (referred to as "hard cider" in the United States). Cider apples are distinguished from "cookers" and "eaters", or dessert apples, by their bitterness or dryness of flavour, qualities which make the fruit unpalatable but can be useful in cidermaking. Some apples are considered to occupy more than one category. In the United Kingdom the Long Ashton Research Station categorised cider apples in 1903 into four main types according to the proportion of tannins and malic acid in the fruit. For cider production it is important that the fruit contains high sugar levels which encourage fermentation and raise the final alcohol levels. Cider apples therefore often have higher sugar levels than dessert and cooking apples. It is also considered important for cider apples to contribute tannins, which add depth to the finished cider's flavour. Classification of cider apples Long Ashton Research Station classification system In 1903, Professor B.T.P. Barker, the first director of the Long Ashton Research Station (LARS) in Bristol, England, established an analytical classification system for cider apples based on tannin and malic acid percentages in pressed juice. This system is divided into four categories, which are as follows: Long Ashton's classification system also included a three-level classification of tannin: "full" for an apple with pronounced tannins (e.g. a "full bittersweet" such as Chisel Jersey, "mild" for light tannins such as Cummy Norman, and "medium" such as Dabinett. Tannins are further sometimes categorised as "hard" or "soft", for bitter and astringent tannins respectively. British cidermakers normally blend juice from apples of multiple categories to ensure a finished cider with a balanced flavour and for the best and most consistent quality. While traditional ciders were made from whatever apples were available locally, the blend of sugar, acid and tannin required for a successful cider is difficult to achieve from any single cultivar with the possible exception of some bittersharps. As bittersharps are rare, a common modern approach is to use a range of bittersweet varieties with some sharps, or a cooking apple such as the readily available Bramley, to balance the acidity. Sharps, with their high acid content, also keep the cider's pH below 3.8 to prevent spoilage; sweets help provide adequate sugar for fermentation to the proper alcohol content. French and Spanish classification systems In addition to the Long Ashton Research Station