Fruit fillings and baked fruit

Why

Heat breaks down the cell walls of fruit, the pectin that holds them together softens and the cells release juice; sugar draws it out of cut fruit even beforehand. Starch, flour or tapioca catch the juice, but only where the filling gets hot enough, cornflour and flour only at the boil, so a filling is done only when the juice bubbles thickly in the centre as well, not just at the edge; juicy berries, cherries and plums need more thickener than apples, and acid together with long baking weakens starch (see the Thickening with starch card). In a strudel toasted breadcrumbs do the same job, and in a cobbler pre-baking the fruit makes it release its juice before the dough goes on. Depending on the variety, apples either hold their shape or fall into purée; according to America's Test Kitchen, gently precooking sliced apples firms the pectin in their walls, so the slices keep their shape in the oven, shrink less and leave no gap under the top crust. The juice sets only as it cools, so a pie cut while hot runs.

How to do it

• Toss juicy fruit with sugar and cornflour just before filling; sour fruit needs more sugar, apples need the least starch.
• In a strudel or a tray bake, lay the fruit on a layer of toasted breadcrumbs or ground nuts to soak up the juice.
• Bake the pie in the lower third of the oven until the juice bubbles thickly in the centre; under a very juicy filling, prebake the base (see the Shortcrust pastry and cold butter card).
• For a deep pie you can first cook the apples slowly, covered and stirred often, until tender but still holding their shape; drain them once cool and they shrink less in the oven.
• Toss sliced apples and pears that have to wait with lemon juice (see the Browning of cut fruit and vegetables card).
• Cut a fruit pie once it has cooled to at least lukewarm; put a cake or bake with quark, eggs or cream in the fridge within 2 hours.

If it goes wrong

Pour juice that has run out of the pie or stayed thin into a small pan, thicken it with a little starch mixed with cold water, boil briefly and serve it with the pie. Return a soggy base to the lower part of the oven for 10–15 minutes, covering the edges with foil so they do not burn. Apples cooked to mush cannot be fixed; next time choose a firmer variety or precook them.