Advances in Cider Flavor: Integrating Apple Raw Materials, Microbial Ecology, and Process Control.

Cider is a low-alcohol fruit wine produced by partial or complete fermentation of apple juice. In recent years, its consumption has grown significantly, especially in Asia. Its distinctive flavor profile reflects a complex interplay of aroma and non-volatile components. The composition of cider is mainly influenced by three factors: raw materials, starter cultures, and production process. This review begins by outlining the composition of cider, covering both its aromatic compounds and non-volatile components. The primary aroma profile is defined by higher alcohols, esters, fatty acids, and carbonyl compounds, while sugars, organic acids, and polyphenols are the key determinants of its taste. Subsequently, it provides a detailed analysis of how the raw material, the choice of starter cultures, and the applied production processes collectively shape the cider's flavor. Research shows that apple variety and maturity influence the levels of sugars, organic acids, and polyphenols, shaping the flavor foundation of cider. To enhance flavor diversity, inoculation strategies have shifted from single-strain fermentation with Saccharomyces cerevisiae to mixed fermentations using non-Saccharomyces yeasts and lactic acid bacteria, either simultaneously or sequentially. Currently, screening non-Saccharomyces strains has become a key strategy to increase cider flavor complexity. Precise micro-oxygenation and nutrient supply regulate microbial metabolism, thereby controlling the fermentation process and the production of specific flavor compounds. In the future, given the untapped diversity of non-Saccharomyces yeasts and lactic acid bacteria in winemaking traits, research in this direction may be key to improving cider quality. In addition, selecting apple cultivars tailored to specific cider styles and exploring pre-fermentation treatments such as cold maceration and enzymolysis may also contribute to enhancing the flavor diversity of cider.