How bad is double-dipping?? Paul Dawson explains @US_Conversation

Is double-dipping a food safety problem or just a nasty habit?

Paul Dawson, Clemson University

What do you do when you are left with half a chip in your hand after dipping? Admit it, you’ve wondered whether it’s OK to double dip the chip.

Maybe you’re the sort who dips their chip only once. Maybe you look around the room before loading your half-eaten chip with a bit more dip, hoping that no one will notice.

If you’ve seen that classic episode of Seinfeld, “The Implant,” where George Costanza double-dips a chip at a wake, maybe you’ve wondered if double-dipping is really like “putting your whole mouth right in the dip!

‘You doubled-dipped the chip.’

But is it, really? Can the bacteria in your mouth make it onto the chip then into the dip? Is this habit simply bad manners, or are you actively contaminating communal snacks with your particular germs?

This question intrigued our undergraduate research team at Clemson University, so we designed a series of experiments to find out just what happens when you double-dip. Testing to see if there is bacterial transfer seems straightforward, but there are more subtle questions to be answered. How does the acidity of the dip affect bacteria, and do different dips affect the outcome? Members of the no-double-dipping enforcement squad, prepare to have your worst, most repulsive suspicions confirmed.

Start with a cracker

Presumably some of your mouth’s bacteria transfer to a food when you take a bite. But the question of the day is whether that happens, and if so, how much bacteria makes it from mouth to dip. Students started by comparing bitten versus unbitten crackers, measuring how much bacteria could transfer from the cracker to a cup of water.

We found about 1,000 more bacteria per milliliter of water when crackers were bitten before dipping than solutions where unbitten crackers were dipped.

In a second experiment, students tested bitten and unbitten crackers in water solutions with pH levels typical of food dips (pH levels of 4, 5 and 6, which are all toward the more acidic end of the pH scale). They tested for bacteria right after the bitten and unbitten crackers were dipped, then measured the solutions again two hours later. More acidic solutions tended to lower the bacterial numbers over time.

The time had come to turn our attention to real food.

But what about the dip?

We compared three kinds of dip: salsa, chocolate and cheese dips, which happen to differ in pH and thickness (viscosity). Again, we tested bacterial populations in the dips after already-bitten crackers were dipped, and after dipping with unbitten crackers. We also tested the dips two hours after dipping to see how bacterial populations were growing.

We tested All Natural Tostitos Chunky Hot Salsa (pH 4), Genuine Chocolate Flavor Hershey’s Syrup (pH 5.3) and Fritos Mild Cheddar Flavor Cheese Dip (pH 6.0).

So, how dirty is your dip? We found that in the absence of double-dipping, our foods had no detectable bacteria present. Once subjected to double-dipping, the salsa took on about five times more bacteria (1,000 bacteria/ml of dip) from the bitten chip when compared to chocolate and cheese dips (150-200 bacteria/ml of dip). But two hours after double-dipping, the salsa bacterial numbers dropped to about the same levels as the chocolate and cheese.

After two hours, levels of bacteria in the salsa were similar to levels in the cheese and chocolate dips.
Paul Dawson, Author provided

We can explain these phenomena using some basic food science. Chocolate and cheese dips are both pretty thick. Salsa isn’t as thick. The lower viscosity means that more of the dip touching the bitten cracker falls back into the dipping bowl rather than sticking to the cracker. And as it drops back into the communal container, it brings with it bacteria from the mouth of the double-dipper.

Salsa is also more acidic. After two hours, the acidity of the salsa had killed some of the bacteria (most bacteria don’t like acid). So it’s a combination of viscosity and acidity that will determine how much bacteria gets into the dip from double-dipping. As a side note about party hosting: cheese dip will run out faster than salsa since more of the cheese sticks to the cracker or chip on each dip. That could reduce the chances of people double-dipping. And yes, this is something we discovered during the experiment.

Should I freak out about double-dipping?

Double-dipping can transfer bacteria from mouth to dip, but is this something you need to worry about?

Anywhere from hundreds to thousands of different bacterial types and viruses live in the human oral cavity, most of which are harmless. But some aren’t so good. Pneumonic plague, tuberculosis, influenza virus, Legionnaires’ disease and severe acute respiratory syndrome (SARS) are known to spread through saliva, with coughing and sneezing aerosolizing up to 1,000 and 3,600 bacterial cells per minute. These tiny germ-containing droplets from a cough or a sneeze can settle on surfaces such as desks and doorknobs. Germs can be spread when a person touches a contaminated surface and then touches their eyes, nose or mouth.

That’s why the Centers for Disease Control and Prevention strongly recommends covering the mouth and nose when coughing and sneezing to prevent spreading “serious respiratory illnesses like influenza, respiratory syncytial virus (RSV), whooping cough, and severe acute respiratory syndrome (SARS).” With that in mind, there may be a concern over the spread of oral bacteria from person to person thanks to double-dipping. And a person doesn’t have to be sick to pass on germs.

One of the most infamous examples of spreading disease while being asymptomatic is household cook Mary Mallon (Typhoid Mary), who spread typhoid to numerous families in 19th-century New England during food preparation. Science has left unanswered whether she was tasting the food as she went along and, in effect, double-dipping. Typhoid Mary is obviously an extreme example, but your fellow dippers might very well be carrying cold or flu germs and passing them right into the bowl you’re about to dig into.

If you detect double-dippers in the midst of a festive gathering, you might want to steer clear of their favored snack. And if you yourself are sick, do the rest of us a favor and don’t double-dip.

The Conversation

Paul Dawson, Professor of Food Science, Clemson University

This article was originally published on The Conversation. Read the original article.

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Paul Dawson explains the #science behind the 5 second rule! #foodonthefloor @US_Conversation

Explainer: is it really OK to eat food that’s fallen on the floor?

Paul Dawson, Clemson University

When you drop a piece of food on the floor, is it really OK to eat if you pick up within five seconds? This urban food myth contends that if food spends just a few seconds on the floor, dirt and germs won’t have much of a chance to contaminate it. Research in my lab has focused on how food and food contact surfaces become contaminated, and we’ve done some work on this particular piece of wisdom.

While the “five-second rule” might not seem like the most pressing issue for food scientists to get to the bottom of, it’s still worth investigating food myths like this one because they shape our beliefs about when food is safe to eat.

So is five seconds on the floor the critical threshold that separates an edible morsel from a case of food poisoning? It’s a bit a more complicated than that. It depends on just how much bacteria can make it from floor to food in a few seconds and just how dirty the floor is.

Where did the five-second rule come from?

Wondering if food is still OK to eat after it’s been dropped on the floor (or anywhere else) is a pretty common experience. And it’s probably not a new one either.

A well-known, but inaccurate, story about Julia Child may have contributed to this food myth. Some viewers of her cooking show, The French Chef, insist they saw Child drop lamb (or a chicken or a turkey, depending on the version of the tale) on the floor and pick it up, with the advice that if they were alone in the kitchen, their guests would never know.

In fact it was a potato pancake, and it fell on the stovetop, not on the floor. Child put it back in the pan, saying “But you can always pick it up and if you are alone in the kitchen, who is going to see?” But the misremembered story persists.

It’s harder to pin down the origins of the oft-quoted five-second rule, but a 2003 study reported that 70% of women and 56% of men surveyed were familiar with the five-second rule and that women were more likely than men to eat food that had been dropped on the floor.

So what does science tell us about what a few moments on the floor means for the safety of your food?

Five seconds is all it takes

The earliest research report on the five-second rule is attributed to Jillian Clarke, a high school student participating in a research apprenticeship at the University of Illinois. Clarke and her colleagues inoculated floor tiles with bacteria then placed food on the tiles for varying times.

They reported bacteria were transferred from the tile to gummy bears and cookies within five seconds, but didn’t report the specific amount of bacteria that made it from the tile to the food.

But how much bacteria actually transfer in five seconds?

In 2007, my lab at Clemson University published a study – the only peer-reviewed journal paper on this topic – in the Journal of Applied Microbiology. We wanted to know if the length of time food is in contact with a contaminated surface affected the rate of transfer of bacteria to the food.

To find out, we inoculated squares of tile, carpet or wood with Salmonella. Five minutes after that, we placed either bologna or bread on the surface for five, 30 or 60 seconds, and then measured the amount of bacteria transferred to the food. We repeated this exact protocol after the bacteria had been on the surface for two, four, eight and 24 hours.

We found that the amount of bacteria transferred to either kind of food didn’t depend much on how long the food was in contact with the contaminated surface – whether for a few seconds or for a whole minute. The overall amount of bacteria on the surface mattered more, and this decreased over time after the initial inoculation. It looks like what’s at issue is less how long your food languishes on the floor and much more how infested with bacteria that patch of floor happens to be.

We also found that the kind of surface made a difference as well. Carpets, for instance, seem to be slightly better places to drop your food than wood or tile. When carpet was inoculated with Salmonella, less than 1% of the bacteria were transferred. But when the food was in contact with tile or wood, 48%-70% of bacteria transferred.

Last year, a study from from Aston University in the UK used nearly identical parameters to our study and found similar results testing contact times of three and 30 seconds on similar surfaces. They also reported that 87% of people asked either would eat or have eaten food dropped on the floor.

Should you eat food that’s fallen on the floor?

From a food safety standpoint, if you have millions or more cells on a surface, 0.1% is still enough to make you sick. Also, certain types of bacteria are extremely virulent, and it takes only a small amount to make you sick. For example, 10 cells or less of an especially virulent strain of E. coli can cause severe illness and death in people with compromised immune systems. But the chance of these bacteria being on most surfaces is very low.

And it’s not just dropping food on the floor that can lead to bacterial contamination. Bacteria are carried by various “media,” which can include raw food, moist surfaces where bacteria has been left, our hands or skin and from coughing or sneezing.

Hands, foods and utensils can carry individual bacterial cells, colonies of cells or cells living in communities contained within a protective film that provide protection. These microscopic layers of deposits containing bacteria are known as biofilms and they are found on most surfaces and objects.

Biofilm communities can harbor bacteria longer and are very difficult to clean. Bacteria in these communities also have an enhanced resistance to sanitizers and antibiotics compared to bacteria living on their own.

So the next time you consider eating dropped food, the odds are in your favor that you can eat that morsel and not get sick. But in the rare chance that there is a microorganism that can make you sick on the exact spot where the food dropped, you can be fairly sure the bug is on the food you are about to put in your mouth.

Research (and common sense) tell us that the best thing to do is to keep your hands, utensils and other surfaces clean.

The Conversation

Paul Dawson, Professor of Food Science, Clemson University

This article was originally published on The Conversation. Read the original article.