Pre-washed, ready-to-eat bagged salads certainly offer convenience. But a recent study in Applied and Environmental Microbiology alarmingly reported that they might fuel the growth of potentially harmful bacteria, at least under certain conditions.
British investigators simulated this scenario in lettuce packages by exposing raw salad greens to the liquid released when the leaves are cut or damaged. This “salad juice,” as they called it, had been contaminated with Salmonella. Even at refrigerator temperature, the bacteria increased dramatically over five days—from about 100 to 100,000 cells, a level high enough to cause foodborne illness.
More disconcertingly, the juice not only allowed the bacteria to stick more to the inside of the plastic salad bag, it also created a coating on the leaves that trapped the bacteria so strongly that they couldn’t be washed off.
Bacteria can get into salad greens via contaminated irrigation water, soil, and human hands during harvest, processing, and packaging. Though this happens rarely, when it does occur it can cause severe, even deadly, illness. A number of headline-making outbreaks have been linked in recent years to packaged salads contaminated with Listeria and other bacteria. Spinach may be particularly vulnerable to such contamination.
So what to do?
It’s really up to growers and packagers to find ways to ensure that salad greens are not contaminated with foodborne pathogens on the way from the field to the bag. In the meantime, the FDA maintains that pre-washed salad greens—the label may say “triple-washed” or “ready-to-eat"—can be eaten without further washing. The rationale is that they have been processed in facilities that are typically more sanitary than the average home kitchen, and home washing may just increase the contamination risk.
But other experts recommend rewashing as an extra layer of safety—as long as you make sure your hands and kitchen surfaces are cleaned well, so as to prevent cross-contamination.
Whether or not you rewash bagged greens, here’s what Berkely Wellness advises:
- At the store, select packages that are refrigerated, have the latest “use by” dates, and show no signs of damage, spoilage, wetness, or slime on the leaves. The leaves should look dry and crisp. Greens that are minimally cut may be less risky than chopped ones.
- At home, keep them refrigerated, and eat them as soon as possible. But toss them if you notice any juices or slime developing.
- Don’t assume packaged organic greens are safer. Several outbreaks of foodborne illness have implicated them specifically.
- Since pre-washed greens are more expensive, you may be better off buying unpackaged greens if you plan to wash them anyway.
- If you buy bagged spinach, consider cooking it. This will greatly reduce or eliminate any risk, depending on how long and to what temperature it’s heated.