And why does there always seem to be at least one slimy piece per container?
I eat salad almost every day. This is not some sort of penance for me—I really love a good salad loaded with a rainbow of veggies and crisp greens. What I don't love is opening a container of mesclun mix or baby spinach and discovering that some of the greens are slimy. The only thing that's worse than seeing slimy greens when I open the container? Eating a forkful of them.
The discovery of slimy greens leads to a conundrum: Do I compost the whole container of greens and find something else to eat, or is it OK to pick through the greens and separate the good from the bad? I confess I usually do the latter and try to salvage as many greens as I can. But is this safe, or am I asking for trouble?
To find out if my mesclun rescue missions are ill-advised, I chatted with James E. Rogers, Ph.D., the director of food safety research and testing for Consumer Reports. Not only does Rogers hold a Ph.D. in microbiology and immunology, he also worked at the Department of Agriculture. In other words, he knows his stuff when it comes to food safety.
Why Do Salad Greens Get Slimy?
According to Rogers, there are two reasons greens get slimy. "It's age—eventually all plants break down," he says. "If you get a dozen roses like I did for my wife for Mother's Day, they will break down. So it's age, but it's also the bacteria that these leafy greens will pick up during growth or processing. They get in there, they love it, and they start multiplying and growing and changing the structure of the plant itself."
Is It Safe to Eat Salad Greens After You've Picked Out the Slimy Pieces?
As gross as slimy greens are, the good news is that the damage caused by age and spoilage bacteria is unlikely to make you sick if you pick out the slimy bits—or, indeed, even if you eat a slimy piece by mistake.
Rogers says he hasn't seen any studies showing an association between eating slimy greens and illness. "I am not going to say absolutely not, because there are exceptions to the rule," he says. There are some people who are very sensitive to eating spoiled food, but, again, he has not seen studies that would suggest you are likely to get sick if you accidentally down a piece of slimy lettuce. (A spokesperson from the Food and Drug Administration confirmed this.)
The bad news? Once the bacteria that spoils food begin to multiply, if there are any pathogenic bacteria (aka the bacteria that can make you sick) on the greens, those bad guys are likely multiplying too.
"Our leafy greens have a lot of bacteria on them—because of the way they're grown, the soil, the air, the animals that walk through the fields," Rogers explains. And those bacteria can include types that can cause serious foodborne illnesses, including Salmonella, Listeria and pathogenic strains of E. coli.
In fact, leafy greens have topped Consumer Reports' list of foods linked to recalls and outbreaks from 2017 to 2022. (Note: If you are very concerned about foodborne illnesses from leafy greens, Rogers suggests cooking them by either quickly blanching them or stir-frying them to kill the bacteria—of course, this works better for hardy greens like spinach, kale and escarole than for tender lettuces.)
And in more unfortunate news, washing greens doesn't help much when it comes to removing bacteria. "Rinsing them typically only removes the dirt, and the rocks and all the rest of that, because the bacteria stick very, very well to the leaves," Rogers explains. "Bacteria can get in between these little cracks and crevices—if you look at the leaf microscopically, you'll see all these dips and ditches and the bacteria get down in there and washing doesn't do anything."
What Should You Do If You Encounter Slimy Salad Greens?
Rogers advises that if half or more of the greens are slimy, toss them all. In addition to being the safest bet from a food safety perspective, throwing away those gnarly greens is also the best bet from a culinary perspective. "Usually when they start getting slimy, the taste is different, the structure is different, they can start to smell," says Rogers. "I know money is tight and groceries are very expensive right now, but why would you want to try eating that?"
However, if the majority are still firm and crisp and just a few bad pieces are sullying the batch, it's likely safe to pick out the slimy ones and eat the rest. Just be aware that the clock is ticking on the remaining greens once you've spotted decay, says Rogers. "I do know that when I see a couple of slimy leaves I'd better use that batch very, very soon," he says. "The bacteria are there, so they're going to spread through the batch eventually."
Salad Greens Shopping Tips
So how do you keep from buying slimy (or soon to be slimy) greens in the first place, beyond the obvious step of inspecting the package well to be sure all the greens you can see look fresh and crisp?
Check the expiration date: Rogers suggests checking the sell-by or use-by date on the greens at the store and choosing the package with the date the farthest in the future, keeping in mind that greens can keep as few as three days once they're home in your fridge.
Ask the grocer: Another trick Rogers and his team at Consumer Reports suggest is asking the people in the produce section of your supermarket when they get shipments of greens. For some markets, that could be once a week, while for others it could be daily. You can also ask when the greens that are currently for sale came into the store.
Consider buying whole heads of lettuce: While buying bagged or boxed lettuce might be more convenient, Rogers says there is some evidence that whole heads of lettuce last longer. They can also be better from a food safety perspective, since you can strip off the outer leaves, which are more likely to be contaminated, and just use the inner leaves.
Keep different kinds of loose-leaf lettuce separate: In many years of picking slimy leaves out of salad blends, I've noticed that the red leaf lettuce always seems to go first. So, if you are buying loose lettuces instead of whole heads, I'd suggest buying each green (or red) individually and blending up your mesclun mix yourself just before serving.
Buy local: Are salad greens in season where you live? Try getting them from a local farm or farmers' market—there's a good chance they'll be freshly picked not long before you buy them, which means they'll probably last longer when you get them home.
How to Keep Salad Greens Fresher, Longer
To keep your salad greens fresh as long as possible, start by keeping them cool on the way home from the store. When you get home, open the container and pick out any wilted pieces. Then transfer the greens to an airtight container lined with paper towels, and stash them in the crisper. Rogers also says to keep your greens away from fruits that produce ethylene gas, like pears, apples and avocados—a hard-sided airtight container should do the trick.
You're unlikely to get sick if you pick a few slimy greens out of a container and eat the crisp ones. But if more than half of the greens are bad, your best bet is to toss them and buy new greens. Increase your chances of a slime-free experience next time by inspecting the greens in the store and choosing a bag with a distant expiration date. Then store the greens properly and consume them quickly to avoid the dreaded slime.