The Man Who Ate Everything - Jeffrey Steingarten [33]
7. Isn’t that a teleological explanation bordering on the religious?
So?
8. When does ripening begin?
Ripening can begin only when a fruit has reached its physical maturity—its full size and intended shape. Fruit picked earlier will never ripen. And even fruit picked when it has reached physical maturity will undergo only some of the changes that we mean by “ripening.”
9. How many changes are there?
Twelve, but I’ll mention only a few.
Ethylene, a simple hydrocarbon gas, is a fruit’s own internal ripening hormone. In ways yet undiscovered, it triggers and coordinates most of the other changes as the fruit sweetens, brightens, becomes juicy and aromatic, grows less acidic and less astringent, exudes a protective wax to slow the loss of water when it finally plops from the tree and is cut off from fresh supplies.
Most fruits soften when they synthesize an enzyme called polygalacturonase, which attacks the pectin cement holding their own cells rigidly in place. The cells slide around, which makes the fruit soft, and spill out their contents, which makes the fruit juicy. Apples lack polygalacturonase, which is why they remain crisp until they degenerate and decay—the stage beyond ripeness when a fruit becomes subject to microbial attack and rot.
Fruits become much sweeter as they ripen. Some of them have already stored up lots of starch or insipid sugars like glucose either on the tree or off; enzymes convert these into intensely sweet sugars like sucrose and fructose. Other fruits fill up with sweet sap only while attached to the mother plant and can get no sweeter after they are picked. And most fruits become less sour as their acids are used up in other ripening processes.
Fruit begins to separate from its parent when a thin layer of cells (known as the abscission zone) is weakened by a specialized enzyme called cellulase secreted by neighboring parts of the plant. Abscission is the natural separation of a fruit from its tree or vine or bush. Very few fruits these days are allowed to remain attached to their mother plant until abscission occurs.
It takes the average fruit only a week or two to go from full maturity to perfect ripeness.
10. But what about limes?
It is a wonder that the lime, with its abundance of acid and only 1 percent sugar, managed to propagate itself at all before the invention of the cocktail, especially because it stays an invisible camouflage green. Most fruits change to a spectacular, attention-getting hue as their chlorophyll decomposes and fades (in ways that nobody understands) and other pigments are either unmasked or quickly synthesized.
As they say in the fruit business, people buy with their eyes. Humans in the grocery store use color as a test for ripeness, which is good practice with strawberries, raspberries, blueberries, and cherries. But some apples redden before they begin to ripen, and oranges can remain green at the peak of ripeness when grown in tropical or subtropical climates (like Florida) without the chilling temperatures that turn the fruit orange (in California). In response to the irrational demands of consumers (including, until a few months ago, me) perfectly sweet and flavorful green oranges are dyed orange or treated with ethylene to “degreen” them on the way to market.
With mature peaches, nectarines, plums, and apricots, the background color of their skin should show no trace of green (except for green varieties). Pay little attention to the red or rosy blush—new varieties have now been bred to turn red long before they are fully ripe. The purpose is to let growers pick immature fruit and dupe the consumer. Some of the sweetest, juiciest peaches and nectarines never color beyond bright yellow.
11. Then what is a fruit lover to do?
Avoid peaches with a green background, and sniff your way around the supermarket. Aroma may be the best way to tell how ripe a piece of fruit was when it was picked. While attached to its parent, fruit synthesizes a bouquet of volatile compounds, as many as one or two hundred in each ripe fruit. At the same time,