Key message <p>Reducing the speed of ripening genetically is a means for adapting grape berry development to the changing needs of the wine industry and in response to global warming.</p> Abstract <p>Understanding ripening patterns and governing ripening speed are central aspects of grapevine (<i>Vitis vinifera</i>) berry biology owing to the importance of grape ripeness in winemaking. Given this reality, it is surprising that the genetic control of ripening remains unknown. Here, we report a major quantitative trait locus that controls ripening speed, expressed as speed of sugar accumulation. A haplotype originating from the species <i>Vitis riparia</i> halves maximum speed regardless of crop levels and berry sizes. In these slow-ripening variants the onset of ripening during midsummer, which is normally completed within a two-week period, takes place so slowly that ripeness is attained under milder weather conditions later in the fall. <i>V. vinifera</i> cultivars show limited phenotypic variation for ripening speed and no selective sweep in the causal genomic region that could derive from domestication or improvement. Closely related species make up for the lack of standing variation, supplying major effect alleles for adapting grape cultivars to climate change.</p>