Bloggers recommend everything from bleach to baking soda. Food safety experts insist that tap water is all you need. What’s the best way to kill germs on fresh produce?
Bloggers recommend everything from bleach to baking soda. Food safety experts insist that tap water is all you need. What’s the best way to kill germs on fresh produce?
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We’re losing the sodium wars—but potassium could help turn the tide (Nutrition Diva #708)
Research references:
Welcome to the Nutrition Diva podcast. I’m your host, Monica Reinagel. There’s a lot of conflicting information online about the best ways to clean fresh fruits and vegetables. Today, we’re going to sort through the research and recommendations. But first, I got a great question from Cary in response to my recent episode on sodium intake.
In that episode, researcher Yanni Papanikolaou pointed out that a potassium-rich diet can blunt many of the negative health effects of sodium and that canned beans, which are often demonized for being high in sodium, are also high in potassium, and could actually help improve the potassium to sodium ratio of our diets.
Cary wondered how rinsing canned beans would affect the potassium content. “Would rinsing reduce the sodium without reducing the potassium,” she wants to know. “Or has the potassium leached into liquid?”
This is a really smart question.
The amount of sodium that is shown on the Nutrition Facts label on a can of beans includes the sodium that’s in the liquid, which most people don’t use. When you drain your beans, more than a third of that sodium goes down the drain. If you also rinse them, you’re reducing the sodium by more than 40%.
But how much potassium are you losing in the process? On the one hand, the sodium is being added to the liquid that the beans are processed in, while the potassium is inside the bean. On the other hand, we have the principle of diffusion, which says that solutes (like sodium and potassium) will move from areas of high concentration to low concentration, eventually reaching an equilibrium.
So, when you put beans in salt water, the concentration of sodium in the bean is much lower than the concentration of sodium in the water, so some of that salt will migrate from the water into the bean. But by the same principle, the concentration of potassium in the beans is much higher than in the water and therefore some of the potassium will leach into the water.
So, by draining the beans, you’re presumably not just losing sodium but also potassium. What’s the upshot in terms of the sodium and potassium ratio of the beans?
If you know me at all, you know that I love questions like this (especially when answering them requires making a spreadsheet!). And fortunately, the USDA has nutrient data for canned beans that have been drained as well as those that have been rinsed. So, I was able to assess the impact of draining and rinsing not just on sodium but also on potassium. And here’s what my latest spreadsheet revealed:
When you drain and/or rinse canned beans, you do lose both sodium and potassium. But there’s a greater reduction in sodium than in potassium. According to the USDA data that I reviewed, draining off the liquid reduces sodium by around 40%, but potassium by only 30 to 35%. Canned beans (with their liquid) already contain a bit more potassium than sodium, and after draining and rinsing, the potassium:sodium ratio is even better.
By the way, while actually rinsing the beans does remove a bit more sodium, the difference is relatively minor. Most of the sodium reduction is achieved simply by draining the liquid. In my opinion, you can probably save yourself the extra step (and the extra water) and skip the rinsing.
And now, let’s turn to Emma’s question about cleaning fresh produce. She writes:
“I've been finding conflicting answers about the best way to make sure the fresh produce I'm consuming is free of dirt, grime, germs, microbes as well as pesticides."
“I see internet articles and forums recommending bleach, baking soda, vinegar, as well as commercial vegetable washes. US government sites say that store-bought cleaners haven't been shown to work any better than water and recommend rinsing produce with cold, running tap water.
“What does the research actually say as to the best way to wash produce? If vinegar or baking soda solutions are realistic options, how long do I need to soak my produce in order for it to actually be effective?”
Emma’s right that food safety experts and government sites such as the CDC recommend washing produce in tap water and insist that home remedies such as salt, vinegar, or lemon juice have not been shown to be effective at removing germs on produce.
And it’s also true that most dirt, pesticide residues, and up to 98% of bacteria can be effectively removed by rinsing produce thoroughly using cold tap water. For firmer produce, adding some mechanical friction from a (clean) brush or even just rubbing vigorously with your (clean) hands also helps. Concentrate your efforts on the stem and/or blossom end, when there is one, as these are areas where dirt and residues tend to collect and concentrate.
For produce that can’t be scrubbed or rubbed (such as lettuce or broccoli), you can soak them in water for a couple of minutes, swishing them around a bit to dislodge any dirt. You also want to be careful not to re-contaminate your clean produce with bacteria from dirty sinks, countertops, or towels.
But Emma’s situation involves a little additional complexity. “I live in Ecuador,” she writes, “where the water is not always safe to drink, and thus I don't have the luxury of just running produce under the tap as I did in the US, which is what prompted my investigation into this topic.”
Rinsing produce in water that is not safe to drink is obviously not a good idea. In that case, you might want to wash your produce in bottled or distilled water—which may or may not be practical.
But, contrary to the CDC’s dismissive statement about home remedies, I actually did find some research showing that a vinegar soak can kill pathogenic bacteria, including the dreaded E. coli bacteria that occasionally cause food poisoning outbreaks. (Interestingly, the study was done by Japanese researchers in the aftermath of a big E. coli outbreak there.)
The study also offers some hints about how long you’d need to soak your produce for it to work. (Although, I want to note that the study was not conducted on actual produce but on bacteria in petri dishes.)
The first thing to know is that the diluted vinegar solution often recommended on food blogs isn’t nearly potent enough to do the job, unless you’re planning to soak your produce for two or three hours. Even straight vinegar (5% acetic acid) required a 25-minute soak to inactivate E. coli bacteria. But there were a couple of ways to boost the effectiveness. One was to add salt to the water.
According to this study, a solution of 1 cup water, 1 cup vinegar, and 2 teaspoons of salt inactivated E. coli in just 6 minutes. Keep in mind, however, that if you’re soaking produce in salt water, some of that salt may end up in the produce. (Remember the principle of diffusion that we talked about with the beans?)
Another way to improve the effect is to heat the water up. The researchers found that it took about 12 hours to inactivate the bacteria using a solution of equal parts vinegar and water at room temperature. Not terribly practical. But a lukewarm solution (100 degrees F) of vinegar and water inactivated bacteria in only 15 minutes. That’s a little more reasonable. And if you’re really in a hurry, adding salt to the lukewarm vinegar water took the time down to just 1 minute.
Again, I want to remind you that this study was done in a bacteria-laden petri dish and not in a typical home kitchen. But it does offer some answers to Emma’s questions about whether vinegar or salt is effective in killing bacteria, what concentrations are required, and how long you might want to soak your produce.
The only way to be 100% sure that all pathogenic bacteria have been destroyed is to thoroughly cook your fruits and vegetables. But nobody wants a boiled Caesar salad. So, I think it’s a matter of understanding and managing the risks.
Here in the U.S., your chances of being infected with E. coli or other dangerous food-borne pathogens from raw vegetables are quite small. Nonetheless, infants, the elderly, pregnant women, and others with weakened immune systems might have a harder time fighting off a food-borne pathogen.
If your resistance is lowered—or you simply want to reduce your risk of being infected to zero—avoid all uncooked fruits and vegetables, as well as unpasteurized dairy products, and be sure that all eggs, meat, and fish are cooked thoroughly. Equally important: keep your hands, implements, and cooking surfaces scrupulously clean.
Even if you're hale, hearty, and risk-tolerant, it would probably be wise to avoid raw vegetables and fruits if some sort of contamination is reported or suspected—such as during an active outbreak—until the source is identified. Otherwise, I think the nutritional benefits—not to mention the culinary pleasures—of fresh raw fruits and vegetables generally outweigh the small risk.
Thanks to Cary and Emma for your questions and I hope you all enjoyed going down a couple of nutrition science rabbit holes with me.
If you have a comment on today’s episode or a question you'd like me to answer, you can email me at nutrition@quickanddirtytips.com You can also leave me a message at 443-961-6206.
I’d also like to invite you to check out my other podcast. It’s called the Change Academy, where we explore the art and science of creating positive behavior change, both in our own lives, and in our workplaces and communities. You can find it on all the major podcast platforms. Just search for Change Academy.
Nutrition Diva is a Quick and Dirty Tips podcast and is supported by a fantastic team, which includes Brannan Goetschius, Nathan Semes, Davina Tomlin, Holly Hutchings, Morgan Christianson, and Kamryn Lacy.