The biochemical and physiological basis for hard cider apple fruit quality

Societal Impact Statement: Fermented “hard” cider is currently experiencing a resurgence in popularity. While there is a long history of cultivating apple trees with fruit quality characteristics intended specifically for cider production, there is a dearth of cider-specific apple production in many emerging cider producing regions, such as North America. To help bolster the emerging cider industry and identify topics that warrant further research, this review article describes the biochemistry and physiology of apple fruit quality from a cider producing perspective. Summary: The United States and Western Europe have a long history of alcoholic “hard” cider production made from the fermented juice of apples (Malus spp.), especially in regions where cultivation of European grapevines (Vitis vinifera) for wine was climatically limited. While all apples contain fermentable sugars, in many regions, cultivars were selected, named, and propagated specifically for fermentation. This review highlights fruit quality attributes that are important for cider production and that are distinct from fresh-market apple fruit and wine grapes. Polyphenol profiles, yeast assimilable nitrogen composition, carbohydrates, organic acids, pectin, and volatile aroma compounds are discussed as they relate to cider quality.