The Man Who Ate Everything (10 page)

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, bitter and astringent compounds called phenols begin to fade away; their main purpose was to discourage animals and microorganisms from eating the fruit before its seed was ready. Neither process happens normally after the fruit is harvested.

The aroma of ripe fruit seems to make the deepest impression on us. The fragrance of a melon I ate in Japan, a peach nudged from the tree on a farm in Sonoma, Rainier cherries jetted from Yakima to a fancy greengrocer in Greenwich Village, tomatoes and strawberries eaten in a field near San Diego—these memories nearly obliterate the intervening months of numbing banality. Aromatic compounds are synthesized as a fruit grows riper, a bouquet of esters, alcohols, acids, and things with names like lactones and aldehydes—all of them capable of becoming gaseous or
vaporous at room temperature so that they can reach the ten thousand odor receptors in the roof of my nasal passages.

In contrast, most vegetables have weak, uncomplicated aromas until you cook them. As Harold McGee puts it, “All cooked food aspires to the condition of fruit.”

12. But doesn’t fruit keep on ripening after you pick it?

Up to a point. When fruit is pulled from the tree or drops of its own accord, it remains alive—capable of respiration, complex metabolism, and reproduction. But its life is drastically changed. The flow of minerals and water is instantly cut off. So is the supply of sugars from those little photosynthesis factories we call leaves. (Fruits that stay green as they ripen can continue photosynthesis in a minor sort of way were the sun not eclipsed as the fruit is piled together or packed into a cardboard box.) Many fruits feel physical pressure on their skin for the very first time. The supply of raw ingredients for synthesizing aromatic compounds changes. In a dizzying shift, the pull of gravity is flipped sideways or upside down.

And the only energy a harvested fruit can draw on comes from its dwindling reserve of sugars, acids, and starches.

No matter what the growers and supermarkets would like you to believe, most harvested fruits do not ripen nearly as well as they would on the tree, vine, or bush, and some don’t ripen at all.

13. Can you be much, much more specific?

Gladly. Fruits can be divided into two groups, according to their style of ripening. “Climacteric” fruits ripen in a frenzied climax of respiration and activity; peaches, apples, and bananas are climacteric. “Nonclimacteric” fruits ripen gradually and decorously; examples are cherries and oranges.
Only climacteric fruit will ripen off the parent plant.
And of these, it is mainly fruit with stored reserves of starch (like apples and bananas) that can grow much sweeter after harvest, although other types of carbohydrates—protopectins in the cell walls and unsweet sugars like glucose—are also capable of sweeting. So there are really five categories of fruit.

14. Who made up these categories?

I did. But they’re quite useful. Category One is fruits that never ripen after they are picked. These include blackberries, cacao, cherries (sweet and sour), dates, grapes, grapefruit, lemons, limes, litchi, mandarins, olives (which don’t belong here because they are not eaten for dessert, but I thought you should know), oranges, pineapples, raspberries, strawberries, and watermelons. Except for watermelons, these are all nonclimacteric, calmly ripening fruits that receive all their sugar from the parent plant, though some may seem to get sweeter as their acidity decreases. Most postharvest changes in these fruits do not improve their quality. Like mushy cherries, they may soften after harvest, but more from decay than from ripening. Except for dates and citrus, they have brief storage lives.

All you can do is to buy them ripe and store them carefully. Mature, fresh berries are plump, with none of their little segments pale or green. Wash them (and cherries) only before serving to avoid damaging the skin and inviting decay. Buy cherries only with stems attached; decay begins at the bared opening. With all citrus, buy firm fruits that feel heavy for their size (they will be juicier with more tasty dissolved solids in the juice) and with thin, fine-pored skin (no point in paying for thick skin). With oranges, color is unimportant; early-season oranges that have been degreened with ethylene to make you feel warmer toward them have a shorter storage life. Don’t mind surface scars and scratches; but soft spots spell decay. If the tiny flower-shaped button at one end of an orange is green, it was picked recently or handled well or both; a brittle, dark button indicates the opposite.

Mature watermelons are well rounded on both ends with dark, waxy rinds, firm but not hard. In a cut piece of melon, the seeds should be dark against intensely colored flesh without white streaks—which makes it much safer to choose a piece of cut watermelon. White seeds are a sign of immaturity.

Category Two contains the one fruit that stands at the opposite extreme. It ripens
only after you pick it
because a chemical
signal sent out by the tree inhibits ripening. It is the avocado. The best way to store an avocado is on the tree. The second-best way is in the refrigerator for up to ten days after you’ve ripened it at room temperature—but only until the fruit yields to gentle pressure, before the skin loosens.

15. How can you call the avocado a fruit if a fruit is an ovary we eat for dessert, and I eat avocados in guacamole and in California rolls at Americanized sushi bars? Do you eat California rolls for dessert?

I don’t eat California rolls under any circumstances. But Brazilians eat avocados for dessert, mashed up with sugar.

16. And the last three categories of fruit
do
ripen after harvest?

Yes. They are all climacteric fruits, and as long as they are picked fully mature in size and shape, they will ripen to some extent and in some ways.

Category Three includes fruits that ripen in color, texture, and juiciness but
do not improve in sweetness or flavor.
These include apricots, blueberries, cantaloupes, casabas, crenshaws, figs, hon-eydews, nectarines, passion fruit, peaches, Persian melons, persimmons, and plums. They will not grow much sweeter after harvest because they contain no starch to turn into sugar. When you ripen them at home, the most you can expect is an attractive, juicy fruit no more flavorful than the day it was picked. If you’re lucky.

But you must buy them physically mature. Mature peaches, nectarines, plums, and apricots have fully developed shoulders (the rounded area around the stem) and sutures (the seam that runs along one side); they have just begun to soften; and the background color of their skin shows no trace of green (except for green varieties). Pay no attention to the rosy blush—it is the background color that matters. You should buy apricots ready to eat, but peaches, nectarines, and plums can be ripened at room temperature in a paper bag.

Category Four is for fruits that
do
get sweeter after harvest— apples, cherimoyas, kiwis, mangoes, papayas, pears, sapotes, and soursops. As they mature, they convert sugars from the plant’s leaves into starch; during ripening, they convert these starch
reserves back into sugar and will grow sweeter, on the tree or off. They are the darlings of commerce because they can be picked mature but unripe, and the advance of ripening can be arrested by refrigeration, sometimes in a controlled atmosphere low in oxygen. Apples and pears do especially well. Pears, in fact, become mushy and mealy when ripened completely on the tree; a period of cool storage before final ripening improves their texture. We are very lucky that pears can be stored, because a ripe pear stays perfect for less than a day.

Most apples in North America are harvested between July and November; cold storage makes them available year-round, often to the detriment of flavor and crispness. Long cold storage followed by ethylene ripening has been shown to produce kiwifruit with less sugar, bananas with less flavor, and apples and pears with less of both.

Buy mangoes when at least some of the green has turned yellow or red (unless you have run across the evergreen variety); avoid those with black spots, which may later penetrate the flesh.

But don’t expect the proper aroma to develop in fruit picked long before it was ripe. Aromatic flavor compounds are not synthesized normally after a fruit is picked; astringent and bitter compounds no longer fade away. That’s why aroma may be the best way to tell how ripe a piece of fruit was when it was picked.

Bananas are alone in Category Five because they ripen in nearly every way after harvest. The world champions of starch conversion, they go from 1 percent sugar and 25 percent starch to 15 percent sugar and 1 percent starch during ripening. And the simple banana aroma (also known as isoamyl acetate) does develop off the tree, though it will not quite compare with the more complex perfume of a nearly tree-ripened specimen.

When most commercially grown bananas are picked, they are mature but still completely green. Turn this to your advantage: buy them green, if you have the time to let them ripen. Hard, green bananas are less likely to have been injured in handling than those that have softened and yellowed on the way. Buy them with the stems fully attached and without splits in the
skin. Ripen in a paper bag until fully yellow with little brown specks. Then refrigerate what you cannot eat immediately, but expect the skins to turn black.

17. Why is fruit sometimes gassed with ethy
le
ne?

The industry prefers the word “treated.” As we have learned, ethylene is a fruit’s own internal ripening hormone. In heavy-breathing climacteric fruit, Categories Three through Five, brief exposure to the gas triggers the fruit’s own production of the hormone and with it whatever ripening potential the fruit possesses. When you place these fruits in a loosely closed brown paper bag at room temperature, the natural ethylene concentrates and speeds the process. Putting a ripe apple or banana in the bag can also help because these fruits generate ethylene like mad. The bag must be permeable enough to allow carbon dioxide produced by the ripening fruit to escape and oxygen to enter. Cut off from oxygen, fruit ferments. That’s the benign side of ethylene. The fruit industry also uses artificial ethylene treatment to hide incalculable sins.

18. Didn’t
you promise to explain the best way of choosing melons?

I was just corning to that. If only there were one simple rule for all melons, nature’s most succulent creation! Remember that melons are climacteric—they can continue to ripen after harvest. But they never get much sweeter than the day they were picked. Buy mature melons—well formed, heavy for their size, without injuries or flat areas. When netted melons like cantaloupes are mature, the netting will be raised instead of flat and the skin between will be tan or yellow, not green. Crenshaws are the king of melons: juicy, perfumed, honeyed, tender. Some mature crenshaws may stay green rather than turn gold, except on the “ground spot,” the place where the melon rested on the earth. The background color of a Persian melon can be light green at
maturity. In the honeydew, that
potentially ambrosial but hard-
to-choose treasure, the skin must be cream colored (not starkl
y
white), without a trace of green. As with other smooth melons, the skin should feel slightly waxy or tacky.