Most people do not realize the crucial importance of freshness when it comes to produce.  In the same way that seeds gradually die, fruits and vegetables go through a similar process as their nutritional content gradually oxidizes or is broken down by the vegetables own enzymes, but vegetables lose nutrition hundreds of times more rapidly than cereals.  Produce was recently part of a living plant.  It was connected to the vascular system of a plant and with few exceptions, is not intended by nature to remain intact after being cut.  A lettuce or a zucchini was entirely alive at the moment of harvest, but from that point, its cells begin to die.  Even if it is not yet attacked by bacteria, molds and fungi, its own internal enzymes have begun breaking down its own substances.

Vegetables, especially leafy vegetables, are far more critical in this respect than most ripe fruits.  All, however, deteriorate much like radioactive material; they have a sort of half-life.  The mineral content is stable, but in respect to the vitamins and enzymes and other complex organic components, each time period or “half life” results in the loss of half the nutrition.  Suppose a lettuce has a half life of 48 hours, two days after harvest only 50 percent of the original nutrition remains.  After two more days, half the remaining half is gone and only 25 percent is left.  After two more days half of that 25 percent is lost.  Thus six days after harvest and a lettuce contains only bout 12 percent of its original nutrition.  A two day half-life is only hypothetical.  Those types of produce I classify as very perishable probably do have a half-life of from 36 to 48 hours.  Moderately perishable produce has a half life of about 72 hours; durable types of produce have half lives of 96 hours or longer.

Vegetable Storage Potential

Very Perishable   Moderately Perishable   Durable
lettuce           zucchini                apple
spinach           eggplant                squash
Chinese cabbage   sweet peppers           oranges
kale              broccoli                cabbage
endive            cauliflower             carrot
peaches           apricots                lemons
parsley                                   beets

The half life of produce can be lengthened by lowering its temperature.  For that reason, sophisticated produce growers usually use hydrocooling.  This process dumps a just-cut vegetable into icy water within minutes of being harvested, lowering core temperature to a few degrees above freezing almost immediately.  When cut vegetables are crated up at field temperatures, and stacks of those crates are put in a cooler, it can take the inside of the stack 24 hours, or longer, to become chilled.  Home gardeners should also practice hydrocooling.  Fill your sink with cold water and wash/soak your harvest until it is thoroughly chilled before draining and refrigerating it.  Or, harvest your garden early in the morning when temperatures are lowest.