Whether fruit holds its shape in the oven depends largely on its variety and ripeness. Juicy varieties with soft flesh collapse quickly in the heat, while firm-fleshed varieties hold up longer. Ripeness works the same way: overripe fruit falls apart, while slightly underripe fruit holds its shape. Slice thickness, leaving the peel on, and oven temperature also affect the result.
What holds fruit’s texture together is the glue-like substance that connects its cell walls. Heat loosens this bond; the cells separate, their water escapes, and the fruit collapses. How quickly it happens depends on two things: the fruit’s water content and how strong those bonds are. Juicy varieties with soft flesh fall apart much faster. The same thing happens in a skillet or saucepan; the oven just makes the process easier to see. That is why two different fruits can turn out very differently after the same time in the oven.
That is why choosing the variety comes first. Firm-fleshed apples that are crisp when bitten hold their shape in the oven; firm varieties such as Amasya apples belong in this group. Soft, tender apples that fall apart in the mouth turn to purée in the oven within a few minutes. Pears have the same distinction. If you do not know which variety you are using, test a slice first and adjust the time based on the result. The point in the season matters for the same variety, too; late-harvest fruit is generally softer.
Ripeness is the second factor and is often even more important than the variety. The bonds in overripe fruit are already loose, so it offers no resistance in the oven. Fruit that is not fully ripe and is slightly firm softens as it cooks without falling apart. That is why fruit for oven recipes is chosen slightly underripe; it will be a little less sweet, but the added sugar balances that. If a fingerprint remains when you hold the fruit, it is too ripe for the oven. When buying fruit, gently pressing it with your palm is a more reliable test than pressing with your fingertip.
Preparation also changes the result. Fruit cut into thick slices or cooked whole holds up much longer than fruit cut into thin slices. If you leave the peel on, it forms a frame around each slice and helps the piece stay together. Sugar draws water from the fruit and slightly firms its surface; lemon juice works in the same direction because the acid makes the bonds loosen more slowly. If you do not pierce the bottom of the fruit while removing the core, the filling will not leak out and the piece will stay firmer.
The final adjustment is in the oven. High heat quickly dries the surface and makes the inside collapse all at once; a more moderate temperature and a little more time soften the fruit evenly. Do not crowd the baking sheet, because slices piled on top of each other cook in their own steam and melt. Remove the fruit from the oven as soon as the tip of a knife slides in; just a few extra minutes is enough to make it fall apart. Do not discard fruit that falls apart; mash it and use it as purée, sauce, or tart filling. If you strain the purée, excess water drains away and the texture thickens.