As apples mature, they produce ethylene gas, which acts as the "ripening hormone" and triggers changes in the fruit.

Ripening is marked by a series of changes: Starch in the flesh converts to sugar. The skin changes color: background green fades to yellow or whitish (variety-dependent).The flesh softens and acidity decreases, making apples taste sweeter. Seeds turn brown, indicating maturity.

Apple varieties ripen from late July to October in temperate regions, with some early varieties ripening around late July/early August, and late varieties into October or November.