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Risky or just gross? A food scientist explains the most common food safety mistakes

A professor of food science weighs in on the worst things we're all doing in kitchen — and what's probably just fine.
Girl giving dog food under table
A bowl or fork that's licked by a dog will be just fine after trip through the sanitizing cycle in the dishwasher. Terry Vine / Getty Images/Blend Images RM

Fess up — raise your hand if you've dropped something on the floor and eaten it anyway, or skipped washing that apple or eaten pizza that sat out all night. Mine's up. But are those things so bad? Robert Gravani, professor emeritus of food science at Cornell University, talked with NBC News BETTER about some of the worst things we're probably all doing in the kitchen, what's probably fine — and how we can all reduce our risk of food-borne bacteria and illness.

You don't wash your produce: risky

Say you grabbed a tomato out of your backyard garden, or you've got a delicious watermelon from the farmer's market. You know where the tomato came from and you don't eat the watermelon rind, right? Before you grab that knife, hold on. “The deal is all produce that you buy either at retail or farmer's markets or even in your home garden should be washed,” Dr. Gravani said. “When you cut it with a knife you'll drag through anything [that's on the skin] as you cut into the flesh. Remember that produce is grown in soil and certainly in the environment we have now [even as] growers are trying to reduce risks of bacterial contaminants, every once in a while we see issues where something goes wrong.”

To reduce risk of introducing bacteria, “wash it under cool running water and pat it dry with a clean towel or paper towel,” he said. “If the produce is firm like melons or cucumbers, use a clean produce brush to brush it off — especially netted produce like cantaloupe because a lot of critters can hide in there.”

The wash won't get rid of everything, he said, but it reduces your risk. Just don't overdo it, he cautioned, with soaps or detergents. Cool water is all you need.

You cut the moldy bit off the cheese and eat the rest: it depends

You're just dying for that last wedge of Camembert from last week's party but — drat — it's turning blue. Blue cheese is good, so this can't be bad, can it? Dr. Gravani wants you to step away from the cheese. Unless it's a hard cheese, like cheddar, that is. It's ok to eat the rest if you cut off at least an inch around and below the mold, he said, being sure to keep the knife out of the mold itself to avoid cross contamination. “Discard the mold and cover the cheese with fresh plastic wrap. The thing here is if the cheese is overwhelmed with mold, forget it — throw it out, it's not worth the risk.”

When it comes to any soft cheeses — think Neufchâtel, cottage cheese, burrata — you're just out of luck. “You can't trust that the mold is localized,” he said.

But why, when stinky Gorgonzola is ok? “Molds used as part of the manufacturing process are not dangerous,” he explained. “They're used to ferment the milk to create the flavors that we enjoy.” Molds not intentionally part of the process, on the other hand? “Some molds produce mycotoxins and they can be dangerous,” he cautioned. Some in fact, he said, can be cancer causing. Moral of the story? Finish the Camembert before it has a chance to go bad.

Pet bowls were found the be the fourth germiest thing in the house and they should be washed daily.

You let Fido lick your plate: mostly ok

If you don't have pets, just move on, nothing to see here. But if your furry friend moonlights as a living, breathing garbage disposal and licks from your dishes, is that horrible? (Asking for a friend.)

Turns out the more serious risk is that they can be “ingesting products that may not be good for their digestive system,” Dr. Gravani said. So be careful what you're feeding them. As for the human members of the family? “We really want to do a good job of cleaning,” he said, but as long as we're washing dishes on a sanitation cycle — or high heat of 160 degrees — breathe easy. “It's ok,” he said.

We're not the only ones who need our dishes sanitized, though. Pet bowls were found the be the fourth germiest thing in the house and they should be washed daily. Yep, daily, and if you're handwashing them they need weekly sanitation.

You had last night's pizza for breakfast — after it sat out all night: risky

“You know what the USDA says,” Dr. Gravani said. “There's nothing magical about pizza. Anything over two hours at room temperature should be discarded.” So why is this such a prevalent practice? “What usually happens is some people don't see any adverse effects so they think it's ok,” he said. But just because you've been lucky so far doesn't mean you're home free. “Organisms that cause foodborne illnesses varying from very mild to significant” can be lurking there with your olives and pepperoni. To be on the safe side, just cram the box into the fridge.

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You're still eating that food with last month's date stamped on it: it depends

“This is so confusing to most consumers,” Dr. Gravani said. “They have no idea what these designations mean. I sure hope at some point we can get a handle on getting people's definitions.” In the meantime?

“Every product has a usable shelf life and at some point the quality begins to deteriorate and that's usually what these dates mean,” he said. “You can eat some of these after the dates but use your senses. If it's significantly lacking in quality you don't want to consume it.” That's a little murky though. Gravani agrees.

“The keeping quality of food still mystifies people because they have no clue.” The good news is there's help available on your phone. Gravani and Cornell worked with food safety partners like the USDA to develop a free app called the Foodkeeper. “It's pretty cool,” he said. There's “basic information about dating but also a rough idea of the keeping quality of a variety of foods. It's really a great app to get a sense of how long folks can keep something.”

You grill your steak and put it back on the same platter: very risky

That happens more than you think, Dr. Gravani said. He's seen it, in fact, when at a barbecue “someone brings out raw meat on a platter and wants to put the cooked meat back on it. I quietly walk the platter back to the kitchen.”

“Certainly raw foods of animal origin contain pathogens,” he said, so letting food you're going to eat touch raw meat is a definite no-go. Not only that, he added, you've got to cook it thoroughly. “How many people have thermometer? Slim to none so it's all eyeballing and we know undercooked hamburger causes illness.” And that holds true whether or not you know where the meat's coming from, he said. “Bacteria doesn't know the difference in a small or medium or large farm, or organic or conventional.”

You dropped your sandwich on the floor and ate it anyway: probably risky

Ahh, the good old five second rule. Dr. Gravani's former student and good friend Donald Schaffner, a food science professor at Rutgers University, is a risk modeler who set out to get to the truth about that old adage. “He looked at four different surfaces and four different foods and he inoculated the surfaces and he dropped the foods for a fraction of a second, less than five seconds, five seconds, and an extended time,” Dr. Gravani said.

“The bottom line was the longer the contact the more bacteria so the five second rule is kind of an oversimplification of what happens when bacteria transfers to food.” But, here's the key. “No matter which food or which surface, they saw bacterial transfer. There was no safe amount of time to leave food on the floor and it is never completely risk free.”

So why do we do it? Just like with the pizza phenomenon, “if people drop it and dust it off and eat it with no consequence that's a learned response,” he said. “But from a microbiologist point of view that's a bad news situation.”

The worst thing most of us do every day

What's the biggest thing we're all doing wrong? According to Dr. Gravani, “the most important thing is just the simple act of handwashing. What a lost practice.”

Before handling food or eating we need to wash our hands for 20 seconds, he said. “It's [singing] Happy Birthday twice.” And that's the hard and fast rule at his house. Even when friends come over to eat, “we say we have a rule … we march everyone to wash their hands.” If we could just bring that practice back, he said, “I think that would reduce a lot of hassles.”

So should we all be aiming for a completely sterile kitchen? Of course not. “I don't think anyone is advocating for operating room conditions in your kitchen,” Dr Gravani said. “What we're saying [is] across the board, the food agencies and health and agriculture departments, let's reduce the risk, there are some common practices we can use. These pathogens are all around now and organisms that we never thought about 20 years ago are now household names. We can still enjoy our food — remember it's social, it's about enjoying the moment and you don't want to make that a sterile lifeless situation. Have fun but do it safely.”

And with that, I'll go wash my hands.