Go ahead and buy bagged greens, but keep them cool.

RODALE NEWS, EMMAUS, PA—Bagged, prewashed salad greens have become a time-saving staple in this country. Exhibit A? The fresh-cut lettuce business has more than quadrupled in the past decade. You can even find organic greens in the bagged produce aisle these days. And, as many of you have discovered, bagged greens aren’t just for salads—witness our yummy recipes for brunch, lunch, side dishes, and dinner entrées below.

However, this healthy trend isn’t without its risks. There are an increasing number of contaminated-produce outbreaks, including incidents with bagged salad greens. Though overall incidence of foodborne illness is on the decline in the U.S., according to the Centers for Disease Control and Prevention, the outbreaks that occur are more often caused by contaminated produce than by bacteria-laden meat.

Bagged salad greens can be completely safe, though, as long as you take a few precautions, suggests a recent U.S. Department of Agriculture study published in the Journal of Food Science. The researchers examined how temperature affected the growth of human pathogens such as E. coli on produce. They also examined if the greens normally showed clear signs of deterioration before the pathogens would grow.

In the study, bagged salads were treated with E. coli, resealed, and stored at both 40°F and 54°F until their “use by” dates. The results? Storing at 40°F limited the growth of E. coli, whereas storing at 54°F actually facilitated its proliferation. The quality of the lettuce kept at that higher temp was still fine when the E. coli growth reached a statistically significant level, so it’s not like you can eyeball the greens to see if they're safe. Bottom line? Maintaining fresh-cut products at 40°F or below is critical for reducing food-safety risks, such as E. coli contamination.