Fresh fruits are made of living, breathing cells. Even when a fruit is picked from the plant, its cells are still alive and continue to carry on natural cell processes like taking in oxygen and giving off carbon dioxide, just as our own cells do.
But when you heat fruit, the cells die and undergo dramatic changes that cause the cells to leak water and soften. The longer you heat the fruit, the more softening and water loss occurs; in other words, the more its texture changes.
Genetics play a big role in the texture of cooked fruit. For example, some types of apples are “good for cooking,” meaning they’ll hold together and have some toothiness, while others quickly turn to mush when heated. But as you’ll see, there are other factors that can affect the texture of cooked fruit, such as its ripeness, when or whether you add sugar, and how you cook it.
Ripe fruit gets tender faster
Someone once asked Jacques Pépin how long it takes to poach a pear, and he responded, “From 2 minutes to 1 hour.” He explained that it all depends on the ripeness of the pear.
Botanically speaking, fruits are the plant’s ripened ovaries, which contain the seeds. (By this definition, many foods that we call vegetables are actually fruits: tomatoes, peppers, avocados, cucumbers, eggplant, snow peas, and snap beans.) When the seeds are mature, many chemical changes occur and the fruit ripens. The green chlorophyll breaks down and bright, alluring colors take its place, delicious aromatic compounds and flavors form, and big starch molecules begin to break down into sweet sugars, or the fruit starts storing up sugar sap to become sweeter.
During ripening, the fruit’s texture changes completely, too. Firm, insoluble substances (hemicelluloses and pectic substances) break down, convert to water-soluble pectins, and dissolve. The fruit becomes soft and tender. Such a sweet, tender fruit will take just minutes to cook.
Unfortunately, much of our grocery-store fruit is picked well before it reaches its perfect state of ripeness. If you’re stuck with rock-hard, odorless, flavorless fruit, don’t be surprised if it takes much longer to cook than riper fruit and needs the addition of other sweet, fragrant ingredients to become palatable.
Adding sugar can preserve a fruit’s shape
In addition to how ripe the fruit is, you should also consider whether to add sugar or ingredients that contain calcium.
Sugar can save cooked fruit from a soft or mushy fate. It does this by slowing down the conversion of those insoluble pectic substances (the cell “glue,” in a sense) into water-soluble pectin. How might you use this to your advantage? Let’s go back to Jacques’s poached pears. If your pears are very ripe, adding sugar to the poaching liquid can prevent them from getting mushy. But if the pears are hard and underripe, don’t add any sugar to the poaching liquid. Instead, poach the pears until they’re fork-tender (or as soft as you want them) and then add sugar to sweeten them.
Fragile fruit cooked with sugar remains intact, while without the sugar, it becomes mush. If you drop fragile berries into a concentrated sugar syrup to cook, the high sugar concentration on the outside of the fruit will pull water out of the fruit but still maintain the firmness of the pectic substances around the cell walls. Without the concentrated sugar syrup, the berries would fall apart as they cooked.
Firmer fruit, however, can shrivel and toughen with too much sugar. A good procedure for cooking firm fruit like apples is to start the apples in water or in a weak sugar solution. This tenderizes the fruit a little but doesn’t draw out enough water to cause shriveling. As the fruit cooks, you can add more and more sugar to keep the pectic substances (and thus the fruit) firm.
Brown sugar, molasses, and hard water, all of which contain calcium, can also maintain texture. Calcium prevents mushiness differently than sugar does. It reacts with the pectic substances to form insoluble calcium compounds that make food firmer. Calcium compounds are sometimes added to canned tomatoes and fragile fruits like raspberries during processing to prevent them from losing their shape. If you’re making a raspberry sauce and you want the fruit to maintain some shape, try cooking the berries with a tablespoon or so of brown sugar. Finally, using pieces of fruit in ice cream can be problematic because of the fruit’s high water content, which causes it to turn into icy pebbles. You can avoid this by soaking the fruit for several hours in a sugar syrup before adding it to the ice cream. This will slow the freezing of the fruit by lowering its freezing temperature.
Fast cooking means firmer fruit
Another way to control a fruit’s texture (although not as effective as adding sugar or calcium) is by how you cook it.
Rapid, high-heat cooking, such as grilling, broiling, or boiling in water, will keep fruit firm, in large part because there’s simply less time for the cells to leak and soften. Immediate contact with high temperatures does something else, too: It kills enzymes in the fruit that would otherwise contribute to the cell’s deterioration. The faster cooking, however, makes more of a difference.
So if you’re aiming for a chunky rather than a smooth peach preserve, you’ll have better luck plunging the peaches into a rapidly boiling sugar syrup than if you cooked them for a longer time by bringing the peaches, sugar, and water to a boil together.
The other side of the coin is that slow cooking and lower temperatures can help soften hard, unripe fruit. Lower temperatures let the enzymes stay alive longer to aid in softening the fruit.