Strawberry soup

Most of the ingredients we buy to cook with are long dead. Thankfully. The meat and dairy products in your refrigerator, the bins of sugar, flour, rice and grains in your pantry, all of the various spices and condiments in the cupboard--none of them is going anywhere, metaphorically speaking.

Except for that rare block of wild, mold-ripened artisanal cheese, any physical changes these foods go through while waiting for us to prepare them are restricted to bacterial spoilage. The main exception to the rule is fruit.

Though we may think of fruit as cheerfully inanimate, its life doesn’t stop at harvest. Fruits continue to change--and even to breathe--long after we’ve popped them into our shopping bags and taken them home.

Fruit ripens. We all know that. But what does it really mean?

Ripeness is not a fixed point but a process. It begins with pollinated flowers forming fruit and ends with rot. As anyone who has eaten a dripping peach will tell you, when caught at the right point, that’s not nearly so disagreeable as it sounds. Here’s the process--call it “A Fruit’s Progress.”

Within several days of being pollinated, a fruit has created all the cells it ever will. It will get larger, certainly, but that’s because the cells expand, not because the plant is making more of them. The cells expand because they are filling up with water. Dissolved in that water is a rich variety of compounds, but of primary interest to us are the starches, acids and sugars.

Technically, at that point a fruit has only matured. It doesn’t begin to ripen until it reaches its maximum size. Ripeness is signaled by a series of changes. Frequently the skin turns color as the green chlorophyll fades, revealing the underlying pigments (this is the same reason some leaves turn red in the fall). The fruit softens too, as enzymes from within the fruit begin to dissolve the cell walls and the pectin glue that holds them together.

Pectin is the reason immature fruit is so hard. It is also the reason why fruit cooked into jams and jellies can thicken without the addition of a starch. As fruit matures, the pectin glues change into pectic acid, which has much less ability to form a gel. Consequently, very ripe fruit does not make good jam.

As the cell walls of the fruit dissolve, moisture is released, making the fruit juicy. At the same time, its chemical compounds intermingle, combining and forming new ones. Of special interest are the compounds that convert the complex carbohydrate starch to the simple carbohydrate sugar. Simple sugars like glucose are converted to complex sugars like fructose and sucrose. Fragrances and flavors develop. Left to itself, the fruit will eventually ripen to the point that it falls to the ground, where it then will either be eaten by animals or finish rotting. Either way, the seeds in the fruit will be scattered to germinate, sprout and grow into new plants.

But ripeness is not a single standard: In different types of fruit, it means different things. As the eminent food writer Jeffrey Steingarten has pointed out, there are five classes of fruit, each ripening in a different way.

Neither is ripeness an unmixed blessing--especially to the people who sell fruit for a living. Obviously, as the fruit softens with ripeness, it can become damaged more easily. This is true not only for accidents that occur during shipping but also for hazards in the field--anything from a poorly timed rain to a hailstorm, even a gust of wind that rubs branches against the fruit.

That is why farmers view the picking of fruit as a race against time. The sooner they can get it out of harm’s way, the better. And because of the ability of many fruits to continue improving in quality after they are off the tree, farmers can pick them even when they appear to be dead green. This is especially true of stone fruits (apricots, peaches, plums and nectarines).

Unfortunately, however, though that fruit might have already converted its starch to an acceptable level of sugar, it probably won’t be as sweet as it would be if it were left to hang longer. And almost as important, it won’t have had time to develop many of those volatile chemicals that help define flavor.

In addition to the more obvious rules for picking fruits--choose those that are heavy for their size; look for firm, smooth flesh--let’s add one more: The closer to you the fruit is grown, the better it is liable to be. Peaches not grown with the expectation of having to be shipped 2,000 miles to market are more likely to be picked later and to be varieties in which flavor is more important than the ability to withstand truck transportation.

There is another way to promote flavor, at least with some fruits. The first step is taking care of them once you get them home. Cold deadens the flavor in fruits such as strawberries and stone fruits, so you should be wary of sticking them in the refrigerator. Leave them at room temperature for as long as you can without courting spoilage. This presumes daily fruit shopping, which is not always practical, to put it mildly.

Another solution is to go with what the supermarkets sell you and then try to trick the fruit. Stone fruit, for example, will soften and develop more complex flavors even if it is picked at a less-than-ideal state: Stick a couple of hard but ripe peaches in a paper bag and leave them at room temperature; in a day or two they’ll be ready to eat.

Because many fruits are still in the process of ripening even after harvest, storage is trickier than it is for vegetables. Any fruit--including the tomato--that is still ripening should be stored at room temperature until it has softened and sweetened as much as it can. Moreover, chilling inevitably damages the enzymes that help create the flavors in fruits like tomatoes, peaches, plums, nectarines and apricots.

It is far better to use such fruits as soon as they are ripe and avoid refrigerating them altogether. Other fruits, such as melons, apples, pears and mangoes, are safe to refrigerate after they’re fully ripe and sweet. If you’re of a particularly morbid turn of mind, it might amuse you to think of the refrigerator as Purgatory.

* Some fruits do not ripen after being picked (berries, cherries, grapes, citrus fruits, watermelon and olives--yes, they’re a fruit).

* One fruit, the avocado, ripens only after it’s picked.

* Some fruits change color and texture and develop more complex flavor after being picked but won’t develop any more sweetness (apricots, melons, figs, peaches, nectarines, plums and persimmons).

* Some fruits do get sweeter (apples, pears, kiwis, mangoes and papayas).

* And then there’s the banana, which will ripen either on the tree or off (though there is little to compare with the flavor and aroma of a banana that’s been allowed to hang to full ripeness).

* Buy these fruits fully ripe: berries, cherries, watermelon and citrus. All except berries can be refrigerated without losing flavor.

* These fruits will soften and develop more complex flavors (though not more sweetness) after picking: apricots, most melons, figs, peaches, nectarines, plums and persimmons. Store them at room temperature until they are as ripe as you want them. After that, refrigeration will extend the life of the fruit, though it will mute the flavor.

* You can refrigerate fruits such as apples, ripe pears and ripe mangoes as soon as you buy them with no ill effects.

* If you buy stone fruit and pears that are hard, you can ripen them by storing them at room temperature in a closed paper bag. Adding an apple will speed the process.

* Fruits can be “cooked” without heat. Sugar draws the water out of the cells, collapsing them and softening the fruit. For this reason, whenever you use sugared fruit in a recipe, either use it immediately after sugaring or be careful to drain off the liquid before adding it.