It's Settled: Dishwashers Beat the Lowly Hand, Almost Every Time

The secret is scalding water that's too hot for the human touch.


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There comes a time in every person's life when the futility of it all hits home, full force. That time for me is every Friday, around mid-afternoon, when I set to tackling the piles of dishes that have accumulated in my sink throughout the week. I have a dozen plates and countless utensils to scrub and scrape. At the end of the day, how clean are they, really?

According to science, my weekly crisis is well-founded: hand-washing doesn't get your dishes as clean as machine washing. And, before washing even begins, your dishes are likely disgusting.

"Any time you're dealing with food, or even just utensils touching a person's mouth, there's the potential for harmful bacteria and even parasites to transfer from food to food, or food to person," said Dr. Keith R. Schneider, associate professor of food science at the University of Florida's Food Science and Human Nutrition department.

Schneider described the formation of "biofilm" on plates left to steep in their own scum for prolonged periods of time. The buildup, he said, "are colonies of bacteria that, once you get established, are harder to remove." In other words, salmonella, E. coli, and a host of other microbes you never hear about on the news can contaminate your plates, utensils and cups, and they tend to grow and become more stubborn over time.

What reliably sanitizes dishes is high heat, at temperatures greater than most people can stand. Past 145 degrees Fahrenheit, water easily and quickly kills bacteria. That's good news for those who own a dishwasher, which run at temperatures ranging from 130-170 degrees Fahrenheit. But most people can't handle water temperatures over 104 degrees, meaning those of us stuck with the pauper's slog of scrubbing our own dishes have a higher likelihood of leaving some bacteria on our plates.

What to do? Is hand-washing dishes truly pointless? Why do I stand, every Friday afternoon, elbow-deep in sudsy water?

Those looking for meaning in life often seek deities; I sought a deity of cleaning, Jolie Kerr, who writes a popular cleaning advice column for lifestyle blog The Hairpin. Kerr has tackled everything from removing leg wax from hardwood floors to de-stinking vomit-stained upholstery, so if anyone has an answer to my cleaning malaise, it would be her. It turns out Kerr does not, in fact, use the more reliable method of cleaning her dishes, as she hasn't had a dishwasher for the past 10 years, so she made the perfect disciple for hand-washing.

Her first point of advice: Quit being such a germaphobe.

"Dishwashers haven't been in existence for so long," she said. "It wasn't like people were dying because of dirty dishes" before the advent of dishwashers. (Even before they were widely used, dishwashers were considered the superior choice, as this 1917 study indicates). Touché.

Kerr echoed Schneider's advice and suggested I use the "hottest water I can," and that, since most people can't tolerate the high heats needed to kill the most bacteria (and most people don't want to ruin their manicures), I consider using dishwashing gloves. Some actually have the added benefit of being quite pretty.

Hot water is one thing. But do not discount your sponge, either.

Your sponge can be "chock-full of bacteria," Schneider said. One 1997 study of 10 U.S. kitchens found that 33 percent of sponges tested positive for E. coli contamination. You're likely scrubbing a bacteria-ridden cleaning utensil all over your bacteria-ridden plate in an attempt to remove bacteria -- the definition of futility. To sanitize a sponge, Kerr suggested microwaving it for 30 seconds.

And soap? Soap doesn't really matter.

"To some extent, soap is soap is soap," Kerr said. Antibacterial soap does have bacterial-killing qualities, but it takes some time sitting on the plate to have any effect. Soap is best at loosening the microbes and causing them to slip from a surface while water washes them away.

The final step to the process: acceptance. These dishes aren't perfect. They may be riddled with germs. But I've been eating from germ-riddled dishes for over two decades now, and I'm not dead yet. So, eating from them for decades more probably won't kill me -- or you.