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The tumble of fresh green peas looks so tempting. They're fat, crisp, and break with a snap. Sure signs of freshness. As you search for the youngest and most tender, gently wiggle your hand inside the pile. You'll likely be surprised at the amount of warmth near its center as even after harvesting, cell activities continue and energy is released in the form of heat.

That heat is a reminder that even after picking, vegetables are still living things. But once harvested, they can no longer renew their food and energy supplies, thus most fresh produce moves quickly past prime condition.

Sweet fresh flavors are fleeting, especially in corn, peas and beans.
Corn stored for just one day at room temperature can lose over 25 per cent of its total sugars. Peas and beans lose even more. As sugar provides the energy for the continuing life processes in all vegetables, it's quickly depleted once vegetables are picked. When vegetables are left on the vine to mature, sugar gradually changes to starch - a form of carbohydrate, which vegetables can store.

Thus, tiny peas are tender and sweet, while mature ones are starchy - perfect for drying, to use later in the year in thick nutritious winter soups.


As soon as vegetables are harvested, they also begin to lose moisture. Celery shrivels. Beans flop. Even tiny carrots soon sag.

Their cut stems also provide a perfect escape route for moisture, so vegetables wilt even faster once sliced. When plant tissues lose water, their nutrients, sugars, and plant acids become more concentrated in the remaining cell sap. Consider the garden-ripe tomato and how quickly it deteriorates. Produce high in plant acids spoil more quickly, because their own acids sabotage cell membranes already weakened by the processes of picking and standing.

In addition, bruised or damaged tissues offer an ideal refuge for bacteria to initiate spoiling. So there's good reason to buy vegetables in the best condition possible, particularly when you don't intend to use them immediately.


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Keeping 'em crisp.
Refrigerator "crispers" reduce moisture loss by keeping the immediate surroundings more humid, reducing moisture loss. Lightly sealed storage bags serve the same purpose. Unless bags are permeable to air, however, vegetables can't breathe properly and water released by the tissues accumulates. And while too little moisture encourages shriveling, too much moisture encourages spoiling. To remedy storing difficulties, perforated produce packages allow the air to circulate freely and excess moisture to escape.

Each month, we've featured a different kitchen science article by the Inquisitive Cooks, Anne Gardiner and Sue Wilson, with tips, facts, and unique ideas to give you a whole new perspective on cooking.

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Temperature also affects keeping qualities.

In most vegetables, refrigerator temperatures just above freezing (34-40° F) retard enzyme action and delay the loss in quality. While deterioration slows, it doesn't stop. Very low temperatures and freezing places vegetables in a state of suspended animation. As most of their water turns to crystals, and the respiratory process halts, chemical activities also slow greatly. Thus, freezing dramatically retards (but does not completely stop) their decline.

In contrast, vegetables of tropical or subtropical origin don't breathe properly when they're stored below 50°F. Thus peppers, eggplant, snap beans, potatoes and sweet potatoes, tomatoes, cucumbers, and squash prefer being stored in a cool, rather than a cold, place.

While new varieties of vegetables suffer less from the rigors of commercial transport and handling than many traditional varieties, there's still validity to the old instruction - "Set the cooking pot to boil, and then run to the garden to pick fresh corn." Most summer vegetables don't take kindly to waiting!

Pick and choose.
So go ahead and be a fussy shopper! Select the freshest produce you can find. Store it with care. And enjoy it as soon as you can.

 

 

Anne Gardiner & Sue Wilson are the authors, with the Exploratorium, of the book The Inquisitive Cook.

 

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