MINNEAPOLIS (WCCO) — With Thanksgiving just around the corner, many people are already thinking about how to make their elaborate dishes. From green bean casserole to mashed potatoes to apple pie, proper food preparation will be necessary to keep everyone healthy.

So, David from Minneapolis wants to know: How much should we wash fruits and vegetables?

“People get ill,” says Ted Labuza, a professor of food science at the University of Minnesota. “If you really want to reduce your chances, washing it good enough is going to maybe reduce the risk.”

Labuza says people should scrub, rather than rinse, their fruits and vegetables for 30 seconds.

“It should really be to one rhyme of Mary Had a Little Lamb,” he says.

In this video from the University of Minnesota Extension, the difference between a quick rinse and deep wash with your hands is dramatic.

“The friction is scraping it off, but you don’t want to scrape it off so much that you’re damaging the fruits and vegetables,” Labuza says.

He says a good wash will remove about 90% of the bacteria. For most healthy people, that’s enough to avoid getting sick from a variety of food-borne illnesses, like E. coli, salmonella and listeria. Older people and children are generally at greater risk.

Studies have shown that water and friction offers a similar clean to commercial vegetable washes or diluted vinegar.

But, in rare cases, the best cleaning won’t help. For example, leafy fruits and vegetables that have been irrigated with bacteria-infected water can be dangerous.

“We do know with things like lettuce and spinach, sometimes the bacteria crawls up through the channels and nothing is going to work there,” Labuza says.

As for fruits and vegetables with inedible peels, like bananas or oranges, Labuza says the outsides should still be washed. He points to a 2011 listeria outbreak in cantaloupe that killed more than two dozen people.

“The organism, listeria was on the outside and cutting the cantaloupe was enough to bring it on the inside,” he says.