There are hundreds of lettuce varieties grown throughout the world and, because they peak at different times of year, there's always a plenitude of this universal salad favorite. There are four general lettuce classifications butterhead, crisphead, leaf and romaine, most of which comprise many varieties. When shopping for any kind of lettuce a general rule of thumb is to choose those that are crisp and free of blemishes. As with all greens, lettuce should be washed and either drained completely or blotted with a paper towel to remove any excess moisture. A salad spinner, which uses centrifugal force to remove water from leafy greens, is a real time-saver for this process. Never allow lettuce to soak, as the water tends to soften some leaves. Refrigerate washed-and-dried greens airtight in a plastic bag for three to five days, depending on the variety. All lettuce is low calorie and most of it is rich in calcium, iron and vitamins A and C. Keep in mind that the darker green leaves contain the most nutrients.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.