Should you wash pre-washed vegetables? A food scientist explains the complicated answer

The heaping bags of fresh kale sold at grocery stores are often advertised as “READY TO EAT”, “TRIPLE WASHED”, or “PRE-WASHED.” But is this really true? Don’t you need to do your own home rinse just to be safe? Probably not, according to food science experts.

According to the Food and Drug Administration (FDA), “Many pre-cut, bagged, or packaged produce items are pre-washed and ready-to-eat. If so, it will be stated on the packaging, and you can use the produce without further washing.”

The Centers for Disease Control states the same conclusion. While there’s never a 100 percent chance of annihilating every microbe on leafy greens, pre-washing actually seems to be pretty safe. And an industry professional and food scientist back up the reliability.

Are “ready-to-eat” veggies actually ready-to-eat?

In short, yes. Evidence shows that these leafy greens actually are ready-to-eat. Martin Bucknavage, a senior food safety associate at Penn State Extension, which is affiliated with Pennsylvania State University, vouches for their safety.

“It is, yes indeed, ready to be consumed,” he tells Inverse.

There’s an incentive, he tells Inverse, for companies to go through the trouble of thoroughly washing their product. Recalls cost companies, retailers, and restaurants millions of dollars (and, you know, harm consumers), so manufacturers are willing to jump through a series of hoops to ensure a safe product.

Still, if someone washes their vegetables again at home, there’s a possibility of re-contamination from microbes in a dirty sink or on a counter where raw chicken had just been prepared. That cross-contamination can make someone sick, at which point they’re more likely to blame the bagged salad’s manufacturer.

How well pre-washing works depends on the green. One 2015 study from the University of California, Riverside found that pre-washing spinach with bleach and water cleansed the leaves of E. coli microbes, meaning they detached from the leaves’ surfaces, but didn’t always kill the bacteria. Some greens may be hiding more bacteria than others because of their dynamic, uneven surfaces.

Bucknavage cautions consumers who shop at farmers’ markets to ask about the produce. “If you're buying [bagged] lettuce at a farmers’ market, I think you'd want to have that conversation with the farmer, you know, ‘Should I wash this?’”

Should you wash pre-washed vegetables? A food scientist explains the complicated answer

He underscores that as long as a bag has the magic words on it, though, it’s safe to eat.

What does pre-washed/triple-washed/ready-to-eat mean, exactly?

All of these labels mean the produce was washed ahead of packaging, and it doesn’t need to be washed again. They really are ready to go straight into the salad bowl. But the pre-wash and triple-wash processes look very different than an at-home rinse. Triple-washed veggies are washed in a solution of water and some kind of disinfectant.

Alex Castillo, a food science professor at Texas A & M University, outlines the triple-wash process:

The product spins dry, which removes droplets, and ships out.

Pre-washing is a safety measure as well as a quality measure. While it kills bacteria on the veggies, it’s also meant to spiff up color and cleanliness. To get into the nitty-gritty, triple-washing is a type of pre-washing. Pre-washing could mean that the produce had a shower of water and/or disinfectant at least, or only, once; triple-washing very likely means that it underwent the three-step process Castillo outlined.

At some produce plants, the greens are rinsed in a large tank that also must be disinfected regularly. A function of the triple wash is to head off any few contaminated products that entered the tank. Maybe 50 spinach leaves in a bunch of hundreds were contaminated. Once they’re washed with water in the tank, the bacteria could spread around and reach other leaves. The two additional washes further scrub and disinfect the produce, and the large tank is also disinfected.

Should I wash pre-washed veggies just to be safe?

This is a tricky question, says Castillo, especially when it comes to products that are already contaminated. “There's no wash whatsoever — triple, quintuple, et cetera — that you can apply or any antimicrobial that you add to a solution that will guarantee you the safety of a product that has been contaminated,” he says.

On the one hand, some bacteria hide in crevices and might evade the triple-wash, which could make another home-wash seem appealing. Consumers could go beyond a water rinse and soak greens in a bowl of water with a drop of bleach or chlorine to disinfect. But, Castillo says, “they need to understand that if those microorganisms were precisely not reachable by the [triple-wash] sanitizer, then that is not going to be successful.” A DIY soak could still reduce microbes, but it may be negligible compared to what the produce plant has already done.

Another point he addresses is that some food is contaminated beyond redemption, and that’s on the industry. “These washes at home may not be sufficient to render the food [safe] ... if it had been contaminated,” he says. In other words, if the produce was already contaminated before it reached the supermarket, washing at home wouldn’t reduce the risk of infection.

Castillo points to five possible causes of contamination: humans, animals, water, soil, and air. For instance, the FDA points to contaminated water irrigation as a contributor to the E. coli outbreak in Romaine lettuce in 2018. These potential entryways for bacteria are in the government’s domain to regulate.

Ample evidence and corroborations from trustworthy science and government sources suggest that there’s no need to rinse pre-washed veggies again at home. But, if you wash greens at home for peace of mind, there’s a right way to do it.

First, wash your hands and make sure your kitchen is clean. Straggling microbes from raw chicken or a dirty sink may re-contaminate the greens. Only wash what you’re going to eat immediately because water hastens deterioration. Wetting leafy greens and putting them back in the fridge only makes them wilt faster. Think about patting dry your leaves as well. And whatever you don’t use, refrigerate right away, otherwise that gives lingering microbes the ability to easily multiply in the room-temperature environment.

“Make sure that you're not re-contaminating it, and then make sure that you're just washing what you're going to use right away,” Bucknavger says.

That ready-to-eat grocery store salad may seem too good to be true, but really, all you need is a fork, and perhaps some dressing.