Agriculture Reference
In-Depth Information
WHAT TO REFRIGERATE
For most of us, putting food in the refrigerator is a reflex, not a considered act. We get
home from the grocery store, sort out the packaged goods and shove everything else in the
fridge - potatoes and peaches, berries and basil, all treated alike. But before you do this,
stop and pay attention to what you're doing. In some cases, it takes only a day at room
temperature to ruin a fruit or vegetable. In other cases, it takes only a couple of hours of
cold. And in a few cases, the question of whether to refrigerate or not depends on the cir-
cumstances.
The best first step is understanding what a refrigerator does and why it can be important.
Even after picking, fruits and vegetables continue to take in oxygen and give off carbon
dioxide and heat. For most produce items, chilling slows the rate of that respiration. Gen-
erally, the closer you can come to 32 degrees, the more slowly respiration will occur. (That
is the freezing temperature of water, but most fruits and vegetables won't freeze until sev-
eral degrees colder because of the sugar they contain.) Different varieties of fruits and ve-
getables respire at different rates, ranging from those that hardly breathe at all (dates and
nuts) to those that seem to be almost panting (asparagus, mushrooms, peas and corn).
At the same time, fruits and vegetables give off moisture, which is called "transpiration."
Slowing transpiration is the purpose of the refrigerator's small, tightly sealed crisper.
Looked at on a cellular level, most plant material is predominantly made up of water held
in little cellulose sacks. When those sacks are full, the fruits and vegetables are firm. When
the sacks start to lose moisture, the fruits and vegetables soften and wilt. Different fruits
and vegetables transpire at different rates, roughly equivalent to their rates of respiration.
Some have thick skins that slow the rate, such as apples, beets, hard-shelled squash, pota-
toes and citrus fruits. Some have hardly any peel at all, most notably lettuces and other
greens.
If it were as simple as remembering the relative rates of respiration and transpiration, the
whole question of whether to refrigerate would be a lot easier. But there is another layer of
complexity. In some fruits and vegetables, chilling actually causes physiological damage.
Refrigerating a tomato, for example, breaks down the chemical compounds that give the
fruit its flavor and fragrance. Once chilled, a tomato may look just as pretty, but it will
never regain its flavor. Potatoes convert starch to sugar if refrigerated and take on a sweet
taste. Some fruits and vegetables that suffer chill damage might surprise you. Cucumbers,
for example, develop soft spots on the surface. So do eggplants. Although most leafy ve-
getables and herbs need to be refrigerated, chilling wipes out basil, turning it black within
a couple of hours.
