Apple Air and Texture

Apples differ from pears in having as much as a quarter of their volume occupied by air, thanks to open spaces between cells in the fruit. (Pears are less than 5% air.) The air spaces contribute to the typical mealiness of an overripe apple: as the cell walls soften and the cell interiors dry out, biting into the apple simply pushes the largely separated cells apart from each other rather than breaking the cells and releasing pent-up juices. Air cells become a factor in baking whole apples; they fill with steam and expand as the apple cooks, and the skin will split unless a strip is removed from the top to release the pressure.