Q Why do fruits such as peaches and melons stop ripening when they are cut open?
A Cutting fruit damages cells and removes the protective peel, exposing the flesh to the environment and altering its chemistry. Some fruit does actually continue ripening. However, it also starts to rot much faster, said Rebecca Harbut, an assistant professor of horticulture and fruit expert at the UW-Madison.
Fruits that can ripen after picking — including melons, peaches, apples, avocados, mangoes, pears and tomatoes — are called climacteric fruits. In these fruits, ripening is hastened by chemicals, primarily ethylene gas, that are produced inside the fruit and convert stored starch into sugar even after picking.
Non-climacteric fruit produce little or no ethylene gas and therefore do not ripen once picked; these stubborn fruits include raspberries, blueberries, strawberries, watermelons, cherries, grapes, grapefruit, lemons and limes.
"If you buy a grapefruit or a pineapple and think it is going to ripen, it simply won't," Harbut said.
Storing fruit in a paper bag will help ripen climacteric fruits because the bag retains the ethylene.
"But the biggest myth is that people think any fruit can be ripened in a bag," she added.
With a pineapple or a grapefruit, "this won't do anything to improve the sweetness or flavor," Harbut said. "The pineapple may become softer and juicier as the fruit breaks down, and the rind may turn yellow, but the flavor will not improve. Pineapple has to be picked ripe. In North America, it's very rare to taste a truly ripe pineapple unless you are in Hawaii where pineapples are grown."