How can fruit look and feel ripe but not be ripe at all? How can we tell if a piece of fruit is ripe? How can we get fruit to ripen? How can we slow down ripening when all the bananas in that bunch on the counter are getting brown spots at once?
As a food scientist, I should know the answers to all of these questions, but on occasion, I slip up, too, and am drawn to a bright orange or soft apricot, only to be devastated when I bite into it. There are guidelines that can help us all make better selections. There also are good and bad ways for storing fruit once it is chosen.
First, a little scientific explanation. Fruits are the seed-bearing ovaries of a plant. It’s their mission to get their seeds distributed as widely as possible. If all of the seeds fall right under the plant, there will not be enough nutrients and sunlight for them to prosper. So several things must happen. Until the seeds are ready to plant, the fruit must stay hidden to keep the seeds safe. To that end, fruit remains hard, sour, inedible, often an almost invisible green among the leaves until the seeds are ready to be sown.
When this finally occurs, fruit needs to enlist the help of animals, humans included, to distribute those precious seeds. To attract animals, fruit becomes brilliantly beautiful, sweet and luscious, with enticing aromas. Animals drawn by the gorgeous colors and smells pick the fruit and carry it away, eating the edible flesh but rejecting the hard, frequently poisonous, seeds. Thus, animals distribute the seeds for the plant.
To become beautiful and irresistible, fruit ripens. It changes in color, texture, aroma, taste, size and nutrient content. All fruit does not change in the same way, though. For example, taste changes that are so important to us can happen very differently in different fruit. Some become sweet when big starch molecules break down into sugars. Others become sweet by storing sugar sap from the plant itself.
This means that fruits such as bananas and apples, which become sweeter as the starches break down into sugars, ripen nicely after picking. Apricots, peaches, blueberries and other fruits that become sweet by storing sugar sap from the plant will never get any sweeter. They may ripen in color and texture but remain as sour as the minute they were picked.
GUIDE TO WHEN FRUITS RIPEN
Fruits that never ripen after picking: Soft berries, cacao, cherries, grapes, citrus fruit, litchis, olives, pineapples and watermelons.
Fruits that ripen only after picking: Avocados.
Fruits that ripen in color, texture and juiciness but not in sweetness after picking: Apricots, blueberries, figs, melons other than watermelons, nectarines, passion fruit, peaches and persimmons.
Fruits that ripen by getting sweeter after they are picked: Apples, cherimoyas, kiwis, mangoes, papayas, pears, sapotes and soursops.
Fruits that ripen in every way after picking: Bananas.
With fruit that cannot ripen after picking, the best we can do is to select the ripest available. We can use color, texture and smell as indicators.
For example, raspberries accumulate anthocyanins, the compounds that give them their rich, bluish red color as they ripen. For riper berries, select those with a deep red color.
Color in melons can be deceptive. Cantaloupes become pale yellow-tan as they ripen, but Crenshaw and Persian melons may remain light green as they ripen. The best indicator of ripeness is probably aroma. Sniff the blossom end — the end away from the stem — to find out if there is a rich melon aroma. A natural waxiness on the surface of some melons also indicates ripeness.
Even with fruit that will ripen after picking, we want to buy the ripest possible.
With color, we usually look for the disappearance of the green hue. As soon as the green chlorophyll breaks down with the acidity changes in ripening, a red or yellow hue begins to appear underneath. However, some apples, including Granny Smith, are bred to stay green and be eaten sour and green.
Fruit such as the tomato makes its own red and orange carotenoid compounds as the chlorophyll breaks down.
Texture also can be a good indicator of ripeness. Hemicelluloses and firm pectic substances, which are the glue that holds cells together, change to water-soluble pectin as a fruit ripens. The cells begin to separate, making the fruit softer.
Can we speed up the ripening of fruit that will ripen after picking? Sure. As it ripens, this type of fruit gives off ethylene gas, which further speeds ripening. You may have noticed that bananas next to apples in a fruit bowl can become overripe overnight. This is ethylene at work.
A ripe banana will speed up the ripening of the other bananas in a bunch so that they all get too ripe at the same time. In fancy food shops, you may see hooks to hang bananas on. These allow some of the ethylene to flow away and not be trapped around the fruit.
My friend Barbara Caleary, a chef trainer in Arizona, told me that when she came home one day, there was a banana lying in the living room, another in the dining room, one in the den and one in the kitchen. She turned to her husband and asked, “Jim, what are bananas doing all over the house?” He explained that he had heard me on the radio and had separated the bananas to slow down their ripening.
We can use this same principle to speed up ripening. To ripen avocados or other fruit in a hurry, warm the fruit by microwaving it for 15 seconds or by placing it in a sunny window. Then place it in a paper bag with a couple of ripe apples and close loosely. You want ethylene concentrated in the bag, but you also want oxygen to speed the ripening. Clear plastic fruit ripeners (plastic domes with some holes) are available and do the same thing.
Because we live in an imperfect world and must make do with fruit that is not truly ripe, we can help nature by adding a little sugar to a recipe. This is what I did in the ice-cold fresh fruit with ginger recipe, which follows. Ginger root gives a magnificent crisp flavor to fruit, and a little sugar makes unripe fruit taste ripe.
Ice-cold fresh fruit with ginger
On a hot summer day, there’s nothing like cold, sweet, fresh fruit. In a clear glass wine cooler or trifle dish, rows of brilliant orange pinwheel slices alternate with rows of strawberries.
Chunks of melon and grapes fill the center, and the top is blanketed with red strawberries to create a dramatic presentation. Prepared a day ahead, this is a great dish for a yard party or barbecue. Sugar enhances the taste of fruit that may not be fully ripe. Ginger root adds a fresh note.
1 (3-inch) piece of ginger root
2 cups sugar
6 navel oranges, peeled and sliced into ½-inch thick pinwheels
1 ripe cantaloupe, peeled and cut into 1-inch cubes
1 ripe honeydew, peeled and cut into 1-inch cubes
1 bunch (about 1 pound) red flame seedless grapes, stemmed
1 quart strawberries, hulled
12 slices candied ginger, finely chopped
In a food processor or by hand, finely mince the fresh ginger root. Place in medium bowl and cover with 1 cup boiling water. Let stand for 30 minutes.
Heat 1 additional cup water with 2 cups of sugar in a small saucepan over medium heat, stirring until sugar dissolves. Remove from heat, pour into a large heat-proof glass container, and stir in 1 cup cold water.
Strain liquid from ginger root into sugar water, pressing ginger against strainer to squeeze out as much as possible of the flavored liquid. Discard the ginger. Place sugar-ginger water in the refrigerator to chill.
You can simply spoon all of the fruit into a clear glass serving bowl, sprinkling it with chopped candied ginger and sugar-ginger water as you go. Or you can make an arrangement.
For the arrangement, press a row of orange pinwheels against the inside of a clear glass bowl or trifle dish. Place cantaloupe and honeydew chunks and grapes in the center to hold the orange slices against the glass and to make a layer. Sprinkle with a little chopped candied ginger.
Arrange a row of strawberries against the glass on top of the orange slices. Again, fill in the center with melon chunks and grapes, and sprinkle with a little candied ginger. Continue alternating layers of orange slices and strawberries, adding melon chunks and grapes until the container is full.
Cover the top with strawberries pressed close together and sprinkle with remaining candied ginger. Pour the chilled ginger-sugar water over the fruit. Cover with plastic wrap and refrigerate overnight. Serve cold. Makes about 10 servings.
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