No rinsing (and re-rinsing), no drying, no chopping. On a busy day when you just want to get food on the table, pre-washed, bagged leafy greens can be a pretty tempting option. But are they less healthy — or even worse, more prone to contamination — than the fresh bunches that you have to wash and chop yourself?
We've all seen those bags of lettuce or spinach that look suspiciously slimy — despite the expiration date being days away. And even if the greens do seem fresh, have they lost nutrients by sitting in those packages for days on end? Find out how pre-washed greens stack up against their fresh counterparts, plus what to get next time you're at the store.
How Bagged Salad Greens Are Processed
The leaves in that bag or clamshell are usually washed not once, not twice, but three times before packaging. The initial wash happens right at the harvesting site and rinses off the first layer of dirt and debris. The greens are then washed twice more at the processing site. At least one of the later washes involves sanitizing chemicals such as a diluted chlorine solution, which is FDA-approved for safety, says Frances Largeman-Roth, RDN, nutrition and wellness expert and author of Eating in Color.
Why the triple wash? "The leaves don't have smooth surfaces that are easy to clean, so a single wash may not be sufficient to get rid of dirt and pathogens hiding in the crevices of the leaves," explains food safety expert Katie Heil, senior editor at State Food Safety. As for the sanitizing chemicals, they're the best defense for wiping out harmful pathogens like E. coli and salmonella that can make their way onto the greens during the growing or harvesting process.
Once the greens are cleaned and dried, they're put into bags or clamshells, stamped with a use-by date and shipped out to stores.
Are Bagged Salad Greens Less Nutritious?
Storing washed and dried greens in an airtight bag or clamshell helps them last longer than whole bunches, which are often sprayed with water while they sit on store shelves. In fact, it's not uncommon to see a bag of spinach or romaine with an expiration date that's seven to 10 days away. But are greens that sit around for a week or longer losing valuable nutrients — even if they still look fresh?
The simple answer: No. "As long as you're buying greens that have been stored properly and you continue to store them properly in your refrigerator at home, there shouldn't be that much nutrient loss," Largeman-Roth says. Indeed, a January 2016 study in Agro Food Industry Hi Tech and a February 2011 study in the Journal of Food Science, respectively, found that lettuces and kale tend to retain many of their vitamins and antioxidants even after a few days or a week.
But Are They More Likely to Be Contaminated?
"Even triple washing doesn't remove all bacteria because they adhere to the uneven surface of the leaves," says Tamika D. Sims, PhD, director of food technology communications for the International Food Information Council Foundation.
And the packaging actually has the potential to make things worse. Juice from cut or crushed leaves are significantly more likely to spur the growth of bacteria like salmonella compared to sterilized water (which might be used to spray fresh greens at the store), found a December 2016 study in Applied and Environmental Microbiology. The juices can make it easier for the bacteria to stick to the leaves or to the plastic packaging.
So, Should I Buy Bagged Salad Greens or Fresh Greens?
Both options are nutritious — so you shouldn't feel like you're picking a less virtuous veggie when you buy pre-washed greens. The sanitizing solution isn't a health concern either, Largeman-Roth says. "The benefits definitely outweigh the risk," she adds.
OK, but what about the whole bacteria thing? Plastic packaging does seem to put pre-washed greens at higher risk for contamination. But if you're strapped for time (or hey, you just don't feel like washing and chopping a gigantic bunch of kale), pre-washed greens are way better than no greens at all.
"The best greens are the ones you're going to eat," Largeman-Roth says. "For a lot of people, myself included, the best greens are the ones that are prepped and ready to go." After all, that head of romaine isn't gonna do you much good if it sits in the fridge for days and eventually turns to mush before you get around to prepping it.
That said, there are some steps you can take to ensure those pre-washed leaves are fresh and free of any potential pathogens:
Scan the package: Make sure your greens are labeled as "triple washed." And pick the greens with the furthest away expiration date, Heil recommends. They'll taste fresher and have a better texture — and they are also less likely to harbor bacteria compared to ones that have been sitting in a bag or box for weeks.
Pick the prettiest ones: Check that the greens look dry and crisp. "Avoid greens that look wet, slimy, yellowed or have an off odor — even if the expiration date says they're still good," Largeman-Roth says. You might want to pick whole leaves instead of pre-cut ones, too, since sliced leaves may be more likely to leak juices that encourage bacteria growth.
Opt for the clamshell when you can: It offers a little more protection than a plastic bag, Sims says. The clamshell packaging minimizes the risk for crushed or bruised leaves that could be more likely to harbor bacteria.
Don't re-wash the greens at home: Doing so puts the greens at risk for getting contaminated by any germs that might be hanging out on your hands, in your sink or on your cutting board. Plus they've already been washed three times, so you're not going to get them any cleaner. "Any bacteria that can be removed was already removed at the bagged greens facility," Sims says.
Store them safely — and use them quickly: "The keys to helping pre-washed greens stay fresh are good sanitation and temperature controls," Heil says. Stash your greens in the fridge as soon as you bring them home and keep them there until you're ready to eat them — ideally, within a few days of purchase. The less time greens spend in their packaging, the less likely they'll be to leak juice that could spur bacteria growth.
- Agro Food Industry Hi Tech: "Nutritional and Sensory Evaluation of Ready-to-Eat Salads During Shelf Life
- Journal of Food Science: "Behavior of Flavonols and Carotenoids of Minimally Processed Kale Leaves during Storage in Passive Modified Atmosphere Packaging"
- Centers for Disease Control and Prevention: "Foods Most Likely to Cause Food Poisoning"
- Applied and Environmental Microbiology: "Salad Leaf Juices Enhance Salmonella Growth, Colonization of Fresh Produce, and Virulence"