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Keeping Fresh Greens Fresh

Wilted lettuce leaf

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from Fine Cooking #100, pp.22-23

In the daily struggle to eat healthfully, salads make it easy. They’re economical, quick, and, because they’re so easy to customize, almost always delicious.

The hard part is dealing with the disappointment of opening the crisper drawer and discovering wilted leaves. Or worse, a pool of green sludge. That’s a quick way to discourage a nice graze. It’s not difficult to keep lettuce happy; in some cases, you can even bring it back from the brink. But first you have to understand what’s going on inside those leaves.

Under the microscope
Leaves are nature’s solar panels, and salad greens are no different. The career goal of a leaf is to have as much surface area as possible with the minimum amount of volume, in order to capture sunlight, absorb carbon dioxide, and release oxygen. There’s not a lot of extra structure, and for that reason, leaves are tender and delicate. The stems are the crunchy bit, because they are the internal pipes of plants: They facilitate the exchange of nutrients between the leaves and the roots.

Healthy lettuce
  Healthy lettuce

The crispness and color of lettuce are determined by the health of its cells. Every plant cell is surrounded by a cell wall, which provides the structure that helps give greens their crisp texture. Inside the cell wall, a semipermeable cell membrane (think of it as a filter) allows the exchange of fluids and gasses that keep the cell alive and productive. At the same time, the membrane contains the various functional parts of the cell, like chloroplasts, the little pockets inside each cell that hold chlorophyll and other chemicals. The chloroplasts’ main job is to convert sunlight to chemical energy for the plant. It’s also the chloroplasts that give lettuce its color—generally green or in the green-to-white range. Much of the volume of a cell is taken up by the cytoplasm and a sac called the vacuole, which holds most of the liquid that fills the cell. When plant cells are healthy and happy, the cells are filled to the brim with liquid, completing the structure that the cell wall started.

Wilted lettuce
  Wilted lettuce

Pop goes the…lettuce
Sound confusing? Well, imagine a bunch of cardboard boxes with no tops or bottoms, all set next to each other in a grid. Inside each box is a balloon that can fill the box. If the balloons are filled so that they push against the sides of the boxes, you can squeeze the box structure and it’s not going anywhere. If you squeeze hard enough, though, some of the balloons will pop. That pressure is what gives lettuce and other vegetables their crispness. By the same token, as lettuce ages, its cells leak liquid, which causes it to wilt.

Know when to fold ’em
The good news is that lettuce is designed to pull in nutrients from its surface. That makes it pretty easy to fix if you’ve let it wilt. Just soak the lettuce in cold water for a half-hour or so, and suddenly it’s rejuvenated.

The cold-water trick is not magical, though. It won’t heal rotting bits, it won’t reverse cellular damage, and it won’t get rid of damage from bacteria. So your lettuce still has to be in essentially good shape, even if it isn’t crisp, before it can be resurrected.

Rotten lettuce
  Rotten lettuce

How to tell? If a portion of the lettuce is much darker green or brown, if it’s liquid rather than solid, or if it just doesn’t look like lettuce anymore, throw in the towel. If it looks pretty much like lettuce except that it’s limp, then you have a candidate for resuscitation.

As long as lettuce cells are whole, the lettuce is in good shape. Remember the balloon analogy? If the balloon is deflated but intact, no worries. However, if the balloon has popped, there’s nothing you can do to fix it. You want to break up the cells when you’re eating the lettuce, not when you’re storing it.

Back, you bacteria
The two biggest threats to cell walls are physical stress and being exposed to liquid for too long. Physical stress because it directly damages the cell walls and makes them susceptible to bacteria, and water because it is a breeding ground for bacteria.

A cell’s cytoplasm and vacuole contain all sorts of nutritious goodies. This is great for humans, since that’s one of the reasons we eat salads. The flip side is that nutrition is also good for bacteria. Because bacteria are lacking in “chewing” and “puncturing” skills, they can’t easily break through cell walls. But when cell walls become damaged, bacteria can move in and have a feast. And bacteria are not on anyone’s list of good salad components.

So buy salad greens that show no signs of damage. Rinse them just before eating, and handle them gently. A vigorous cleaning can cause damage from handling or by scraping dirt or sand across the leaves. Don’t cut or tear the greens before you’re ready to eat them.

Let’s spend a moment on the tearing versus-cutting debate. Some experts advise tearing greens into bite-size pieces, on the principle that cutting will damage the cells, while tearing will occur naturally between the cell walls without damaging the membranes. Others insist you should cut greens because in tearing them apart, you squeeze cells with your fingers, causing the cells to burst. I say: It doesn’t matter. Just be as gentle as you can as close to eating time as you can.

Crisp tips

• Store lettuce whole (uncut and untorn); it will last longer.

• Wrap lettuce in paper towels and keep in an airtight container in the fridge.

• Soak greens in cold water before serving to fill their cells with any water they’ve lost in their journey from field to table, making them as crisp as possible.

Sound advice
Storage is much less controversial. Keep greens in an airtight container in the refrigerator. It’s a good idea to wrap them in paper towels to absorb excess moisture (remember, too much water breeds bacteria) and to keep the leaves from touching the plastic directly (to prevent condensation).

Understanding your salad greens will help you keep them fresh, and keeping them fresh will help ensure that you’ll eat them regularly. That will make you healthier, happier, and generally a better person. Between that and the fresh taste of a good salad, what more do you need?

Illustration by Aude Van Ryn

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  • User avater
    Bowl_of_Plenty | 08/18/2009

    Check out this video of lettuce getting rejuvenated in water:
    http://blog.khymos.org/2008/04/09/osmosis-in-the-kitchen/

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