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What’s the Best Way to Wash Microbes off Your Produce?

Photo credit: Bartlomiej Berczynski (barthetzk), via freeimages.com
Photo credit: Bartlomiej Berczynski (barthetzk), via freeimages.com
Photo credit: Bartlomiej Berczynski (barthetzk), via freeimages.com

Note: This post is part of an ongoing series in which we try to answer questions about the science behind food – from farm to fork. If you have a food-related question, please let me know at matt_shipman@ncsu.edu.

Short version: You can use water to wash off your fruits and veggies – but it may not make a big difference, in terms of food safety.

Here’s the question we got: “What is the most effective means of cleaning fresh produce at home to remove micro-organisms that could make you sick?”

“Vigorously rinsing the produce under running water is the most effective way of removing the microbes that cause foodborne illnesses – you don’t need soap or any special cleaning products,” says Ben Chapman, a food safety researcher at NC State. “But while washing your produce may remove some pathogens, it doesn’t eliminate risk altogether.”

“At best you get a two log reduction – that’s a 99 percent reduction in microbes,” Chapman says. “That seems good, but it’s not great. While washing can help reduce pathogen contamination, it shouldn’t be relied on as the only control measure.”

By comparison, cooking food results in a six log reduction in viable microbes. That means the population of viable microbes gets cut by 99.9999 percent(!).

The difference between 99 percent and 99.9999 percent is important because some fruits and vegetables can be contaminated with thousands of microbes. And we know that, on average, most microbial food-borne illnesses are caused by foods that are contaminated by only 20-30 organisms. So washing off 99 percent of the microbes doesn’t help much if a food was carrying thousands of microbes to start with.

This is why people who are immunocompromised, such as some chemotherapy patients, are often discouraged from eating raw produce; there is no way to make raw produce as safe as cooked fruits or vegetables in terms of microbial contamination.

Your best bet for reducing risk is to be an educated consumer and buy from a reliable producer that understands how to minimize the chances that produce will be contaminated.

Don’t be afraid to ask questions at the farmer’s market or in the produce section of your grocery store! Here’s a list of food safety questions that could help. If they don’t know the answer to your questions, you may want to shop elsewhere.

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