What Happens When You Double Dip That Chip?

33:44 minutes

aerial view of spread of food with multiple hands reaching for it
Credit: Shutterstock

You’ve probably heard of the five second rule, when you drop a cookie on the floor and take a bite anyway because it’s only been a few seconds. What about when you’re at a party and you see someone double dip a chip in the salsa? How much bacteria does the double dip and the five-second rule spread around?

Biologists Paul Dawson and Brian Sheldon investigate these questions their new book, Did You Just Eat That?: Two Scientists Explore Double-Dipping, the Five-Second Rule, and other Food Myths in the Lab. They talk about how bacteria spread around in our everyday lives and what can be done for food safe handling in our homes.

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Segment Guests

Paul Dawson

Paul Dawson is co-author of Did You Just Eat That?: Two Scientists Explore Double-Dipping, the Five-Second Rule, and other Food Myths in the Lab (W. W. Norton & Company, 2018). He’s also a professor of Food Science at Clemson University in Clemson, South Carolina.

Brian Sheldon

Brian Sheldon is co-author of Did You Just Eat That?: Two Scientists Explore Double-Dipping, the Five-Second Rule, and other Food Myths in the Lab (W. W. Norton & Company, 2018). He’s also a professor emeritus of Food Microbiology and Poultry Science at North Carolina State University in Raleigh, North Carolina.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. If you’re a Seinfeld fan, perhaps you remember this classic moment. George is at a party, just like the kind you’re going to be attending this holiday season. People are schmoozing, eating the crudités, then he’s caught double dipping his cracker into the dip. 

GEORGE: Double dipped? What are you talking about? 

TIMMY: You dipped the chip, you took a bite, and you dipped again. 


TIMMY: That’s like putting your whole mouth right in the dip! 

IRA FLATOW: Well, does double dipping a chip really infect the dip? What about the five-second rule, where you drop some food onto the floor? Is it too germy to eat? And how about this holiday favorite– does spiking the eggnog kill the bacteria? You know, the alcohol in it? My next guests are two biologists who investigated these food questions we’ve all thought about in their new book Did You Just Eat That– Two Scientists Explore Double Dipping, the Five-Second Rule, and Other Food Myths in the Lab. 

So if you’ve got questions about the bacteria and germs around us this season– like, when you blow out the candles, do you spread your germs all over the cake? Hmm. These two guys are here for you. Do you have a food or germ myth you’re wondering about? Our number is 844-724-8255. 844-724-8255. Or you can tweet us @SciFri. 

Let me introduce my guests. Paul Dawson is Professor of Food and Science at Clemson University in Clemson, South Carolina. Brian Sheldon is Professor Emeritus of Food Microbiology and Poultry Science at North Carolina State University in Raleigh. Welcome to Science Friday. 

BRIAN SHELDON: Thank you, Ira. Glad to be here. 

PAUL DAWSON: Thank you, Ira. My pleasure 

IRA FLATOW: Paul, you actually teach a class about these questions we all think about, like the five-second rule and double dipping? 

PAUL DAWSON: In a sense, yeah, we have a program called Creative Inquiry here at Clemson. And the purpose of the class is to expose students to research. So rather than or in addition to going to a lab– we all remember our labs back when we were in high school and college, where you kind of receive a list of things or of things to do, in these classes, the students come and they address a problem or an issue, everyday issue, and they could get some choice in that. And we attacked that in the lab so to speak with the scientific method. And as you mentioned some of these in the intro, these are ones we’ve used to teach the students how to do research. 

IRA FLATOW: Let me go right into that clip from George Costanza, double dipping. Let me ask right out, is that a dangerous thing to do? 

PAUL DAWSON: Well, I guess, “dangerous” is how you approach it. But the fact of matter is we did find that you do transfer oral bacteria to the dip. So if the people in the room are your good friends and you feel comfortable exchanging saliva with them, if you will, then it’s not a problem. But as you know, at this time of year in particular, we’re concerned about the cold, flu, and influenza, and the common cold and so forth. So I guess there is some risk in doing that. 

IRA FLATOW: Brian, I was going to ask, what are the most common bacteria and viruses that like to munch on our food? 

BRIAN SHELDON: Well, that’s quite a variety. There’s thousands, literally millions of organisms that comprise our bodies itself has been estimated somewhere like 5 times 10 to the 30th organisms on this planet. And about 39 trillion actually reside in or on our bodies. And fortunately, about 99% of those are seemingly harmless or actually have beneficial uses for us. Only about 1% of the known bacteria and viruses actually are pathogenic or disease causing. 

So relative to– I mean, these organisms are just like us. They need to metabolize. They need a nutrient source. And they carry out all the functions that we do. They reproduce. They communicate. They are able to move. And so consequently, they’re going to be in about every environment that we’re in. And we can’t do anything without them because they are part of us. And it’s just a matter of is that 1% of the organisms that– did that land in that dip, like Paul said? 

Essentially, is there a cold virus, or a flu virus, or you pneumonia virus, or bacteria in that dip? Or anything that we touch, too, could contain these organisms. Really, you’re playing the odds. There’s always a risk associated with anything we do in life. It’s a matter of how great is that risk. And of course, the risk for us also depends upon our immune systems themselves. If we’re very aged, or very young, or immunocompromised in some way, obviously, we’re going to be at greater risk in engaging in these types of practices like double dipping and just everyday life. 

IRA FLATOW: Let me hone in on a few things that people do or people think about. Is there a time, a set limit, a time that you can allow the food to stay outside on the serving tables before they go bad? Or does each food have its own clock on it? 

BRIAN SHELDON: This is Brian again. 

IRA FLATOW: Brian, go ahead. 

BRIAN SHELDON: I’ll jump in on that one, and Paul can follow with additional information if he cares to. Well, the recommendation is that the food not stand on the countertop or the picnic table for more than two hours. That’s dependent upon what the atmospheric conditions are, the environment. If you’re out there in that proverbial summer picnic and it’s 90-plus degrees, and you have a, let’s say, a meat-containing product, a chicken containing product is sitting out there at 90 degrees, we did some calculations. If you had, like, 40 salmonella cells per gram of material, after four hours, you would have something like 2.6 million cells. 

IRA FLATOW: Oh, but we’re inside in the holiday season? Inside someone’s living room or kitchen or something? 

BRIAN SHELDON: The recommendation is still– 

IRA FLATOW: Still two hours? 

BRIAN SHELDON: –to be within two hours. And some, actually, if the conditions are too favorable for growth of the organism, within 30 minutes, you ought to be refrigerating it. 

IRA FLATOW: Wow. Do you want to add anything to that? 

PAUL DAWSON: Well, yeah, I guess, obviously we’re talking about casseroles and food that are perishable. If you left an M&M out on the table, that’s not going to be a problem. Some foods are, what we call, shelf stable. So yeah, I mean, obviously, we are considering the casseroles, like Brian mentioned. 

IRA FLATOW: We have a lot of people calling in. Let’s go to the phones early. Josiah in Harrisburg, South Dakota. Hi, Josiah. 


IRA FLATOW: Hey, there. 

AUDIENCE: OK, so my question was, is it bad if you take the– like, if you’re cooking some food and then you take it out and, give it a taste, and then put the utensil back in, is that bad? 

IRA FLATOW: Mm. Good question. You’re tasting with a spoon. Is that a bad thing? Because it’s going back into the sauce or whatever you’re making. 

PAUL DAWSON: Yeah, that’s actually kind of one of the chapters we did a study on– sharing food, if you will. Because we talk about, in some cultures, it’s common, even our culture, to share food or actually taste food as was mentioned by the caller. So again, we go back to the double dipping. You are transferring oral bacteria to the food when you do that. So– 


PAUL DAWSON: –again, if you’re going to keep– Brian can jump in again after I finish. But if you continue to cook the food– 

IRA FLATOW: But doesn’t it get destroyed by the heat, if you’re boiling soup or something? Doesn’t it? 

PAUL DAWSON: Oh, yeah, if you continue to cook it and cook it after, but if it’s like the last few minutes of the cooking or whatever, you’re probably not going to. Because as mentioned, time and temperature, both growth-wise and destruction-wise for bacteria and viruses, is a time and temperature combination. So 10 seconds at a particular temperature is not the same thing as a minute or 10 minutes or whatever. So tasting’s not bad if you’re going to cook it fully after that. 

IRA FLATOW: That’s why you see professional chefs. When they want to taste something, they take a piece of bread and dip it in. And then, they taste it. They don’t actually take this spoon or something. 

PAUL DAWSON: That’s probably a good practice. 

BRIAN SHELDON: At least we hope they do that. 


IRA FLATOW: OK, Paul, let’s talk about the– everyone has heard of the five-second rule, right? You can eat something off the floor as long as you pick it up within five seconds. And you actually tested that out. There’s a history to this idea, right? Where did it come from? 

PAUL DAWSON: Yeah, we did. That was also a fun part of the book. In most chapters, we go back and we talk about food habits or practices, and, like, blowing out birthday candles, or the five-second rule. We try to figure out where it started. And, really, we couldn’t find it. I don’t there is a definitive origin of the five-second rule. But there are some writings in history– actually, Genghis Khan made some statements about if food was left– if food was prepared for Genghis Khan, then it was good enough to eat, no matter how long it stayed on the floor. So he had the Khan rule. 

And then, really, there’s a video or a tape of Julia Child dropping a potato pancake on the stovetop and making a comment, it’s fine to put it back on the plate if nobody’s in the kitchen with you. So that may have been the origin of that. But we actually– there’s kind of two questions there, and that’s kind of part of the learning of the creative inquiry studies we did. You asked the question, is it safe to eat if you pick it up in five seconds, whereas we really tested, is bacteria transferred if you pick it up within five seconds? And those can be two different things because it depends on, really, what surface you drop it on. 

So we really, in our study– and again, part of the nice thing is I learn a lot, and the students learn how to go about and create an experiment. So we went to a local home supply store and bought small, like four or five inch square pieces of carpet tile and wood flooring, took them back to the lab, sterilized them. He laid them with salmonella, and then actually left– did two things– left the salmonella on those surfaces for different periods of time before dropping food– baloney in our case and white bread, and then picking it up within 5 seconds, 30 seconds, or 60 seconds, and then measuring the transfer of bacteria to that food. 

And again, probably not surprising to most people is it was transferred within five seconds instantaneously, essentially. So if there’s contaminated– if the surface is contaminated, the five-second rule was a myth. 

IRA FLATOW: Yeah, there you go. Let’s go to the phones to Jimmy in Inglewood, New Jersey. Hi, Jimmy. 

AUDIENCE: How are you doing? Great show, great topic. So just to piggyback on that transfer rule. Say if I had a slice of pizza in the kitchen and I dropped it face down on the floor– the cheese, and then I pick it up and run some cold or hot water over it. And again, just piggybacking on that, what would happen? 

IRA FLATOW: Yeah, can you rinse stuff off that’s dropped on the floor? 

BRIAN SHELDON: Well, I think, obviously, you’re going to have some impact. You’re going to be able to rinse some of the organisms off. But be able to get a totally– let’s just say, use the word “sterile” product by just simply rinsing, you’re not going to be able to achieve that. 

And then, it comes down to the question of, what was on that floor to begin with? There very well could not be any pathogenic organism. But then again, there could be. If you have a dog or a cat that’s in the family and they’re going back and forth across the floor, and of course into their litter box, there’s a good chance there could be a pathogen in there. The rule of thumb is that, when in doubt, throw it out. So that may be– 

IRA FLATOW: It’s not just a dog and cat. We walk in with our shoes from the street, right? 

BRIAN SHELDON: Yes, yes. I didn’t want to blame the dogs and cats. Obviously, we carry a lot on our shoes as well. 

IRA FLATOW: Let me ask you about the candles question. If you blow out the candles on a birthday cake or whatever kind of cake, are you spraying the whole cake with germs? 

PAUL DAWSON: Yes. Short answer to that is yes. In fact in our studies– and this is a fun part, too– just a little background on that– we were concerned about actually the top of the cake, the icing, so we created a faux cake, if you will. We had Styrofoam and then layers of a sterile aluminum foil, and then actually put icing on there. And we use Styrofoam so we actually stick candles through the icing to simulate a party, but we try to do it as real world, if you will, as we can, and actually had the subjects eat a slice of pizza or take a bite of a slice of pizza, kind of get the saliva going, and then blow birthday candles out as if it were a birthday party. 

And you might guess, some of these studies we did, you find high variation from person to person. In this case, an average of 3,000, almost 3,000 bacteria are transferred to the cake versus virtually none. And we ran a control, if you will. We did the exact same thing, set it up with the icing and candles lit and everything, and just removed that without blowing on there and compared blowing on there versus not blowing on there and found, like I said, almost 3,000 bacteria on the cake that was blown on on average. 

But actually, one cake, we found 37,000 bacteria. So huge variation as you might expect. And you can imagine a scenario, we have a very young child or very– we use a scenario in the book where you have a 90-year-old grandmother or grandfather having a birthday. So there’s actually a lot of candles on there. And then, they enlist the help of their grandchildren to help them blow their candles out. So you’re getting a lot of saliva going. 

IRA FLATOW: Wow, yeah. 

PAUL DAWSON: And actually, just talking like we are now, you’re generating what we called bioaerosols, and they are very low– they’re large enough compared to a bacteria, the bacterium– bacteria in your mouth, oral bacteria, to ride along. So we’re generating– 

IRA FLATOW: I have to generate a bioaerosol at the moment to remind everybody that I’m Ira Flatow. This is Science Friday from WNYC Studios. Continue that thought, please. 

PAUL DAWSON: OK, so you can imagine then, if we’re just talking now, we’re generating those into the air. First of all, blowing we’re doing– certainly, you’re blowing forcefully to blow candles out. You’re going to be blowing oral bacteria and bioaerosols on the top of the cake and direct it in that direction. 


BRIAN SHELDON: And as Brian mentioned earlier, there are known, some infectious diseases, that are carried from saliva– tuberculosis, pneumonia, flu, SARS, Legionnaires’ disease. And again, I guess– I’ll step back a little bit. I’m not trying to scare anybody. Because you can tell by the name of the book we’re not trying to scare people, but we are– there are some serious topics. And if someone’s at a birthday party who is immunocompromised, you probably want to be a little more cautious of blowing the candles out or serving them the cake. 

IRA FLATOW: Well, that was my question. After you’ve done all this research and you specialize in this, are you more germophobic now or less fearful? 

PAUL DAWSON: I think, for myself, this is Paul, I’m less fearful– I mean, nothing new. As Brian said before, we live our lives– pretty old now, I guess– and eat three meals a day, 365 days a year. And sure, we’ve probably all had a bout with foodborne illness, but in general have been very healthy. And I’m not going to change too much what I do. I am aware of– in public places, I think I’ve always been aware of it, a little more aware an adult and have done some studies– washing my hands, and maybe not touching some surfaces before I eat, and not touching my face with my hands and so forth. But in general, I’m not going to not eat a birthday cake because someone blew the candles out. 

IRA FLATOW: Our number– I’ve got about a minute till the break, so if you can get that in, that comment, go ahead. 

BRIAN SHELDON: The only thing I have to say is that you remember when I gave the statistics about 99% of the microorganisms are seemingly safe to us and only about 1% are problematic, so I kind of use that rule of thumb. And as Paul said, I like to take some caution, and in cleaning my hands, and what I touch at a restaurant– menus, et cetera. 

IRA FLATOW: Right. Well, we’ll talk more about that. Because I have lots of phone calls, lots of tweets coming in about shaking hands during the holiday. I’m looking at someone who’s fist pumping. Is that better than the handshake? All kinds of stuff people want to know, because we’re going to be greeting– and, well, how about kissing on the cheek? We’ll get into some of the stuff after the break. Stay with us. 

I’m Ira Flatow. You’re listening to Science Friday. We’re talking about the book, Did You Just Eat That, Two Scientists Explore Double Dipping, the Five-Second Rule, Other Food Myths in the Lab with the Paul Dawson and Brian Sheldon, a great book. I recommend everybody get a copy of this. 

I want to go to a tweet that’s actually close to my heart because I’m sort of guilty of doing this. It comes from Mary Kate. It says, my step mom used to get mad at my dad for reaching into the pickle jar with his hands. He’d reply, if this can pickle a cucumber, it can pickle my germs, too. I mean, I want to know, as someone who ferments my own pickles and I’m guilty of doing that, how right or wrong is he? 

BRIAN SHELDON: This is Brian. I’ll take a stab at this, and Paul can follow. It really depends upon the pickle we’re talking about. If we’re talking about a dill pickle versus a sweet pickle, the composition of the dill pickle is going to have much more acid in it, vinegar in it, not only besides the fermentation that occurred, but it’s the acids really controlling the microbial growth. 

And if we’re talking about a dill pickle, you’re probably are going be able to get– and it also comes down to how dirty the person’s hands are. But for the most part, most bacteria, pathogenic organisms, cannot resist or cannot survive high acid content products such as dill pickle juice. 

IRA FLATOW: Is that why ketchup can sit out forever almost? Because it’s got a high acid in it or other condiments, and they don’t go bad? 

BRIAN SHELDON: Paul, you can take this them. 

PAUL DAWSON: Yeah, well, exactly. Even mayonnaise has a high enough acidity if you don’t add other things to it. Mayonnaise gets a bad name, but if it’s just mayonnaise itself, it has a low pH, if you will, or high acidity. And that prevents bacteria– it’s self-stable. You can kind of walk through a grocery store and see things that are what’s called “shelf-stable” that aren’t refrigerated or canned, hadn’t been heated– like you mentioned, ketchup, mustard, and others. So yeah, that’s exactly why. 

IRA FLATOW: So in a picnic, it’s not the mayonnaise that goes bad sitting out with the potato salad or the chicken salad? 

PAUL DAWSON: Well, yeah, well, Brian, you can jump in after I– yeah, the potato– you mixed potatoes in there or chicken in there, and that’s diluted or buffered acidity. So then, it’s no longer– the environment is no longer a low enough pH to prevent growth. And you’ve probably– you may have inoculated the mixture with something– by adding something to that salad. So I would– I’m just kind of doing this off the fly here in my mind, but I imagine if we did an experiment and tried to mix something in with ketchup, you might have the same result if you dilute out the acidity. 

IRA FLATOW: Let’s move on to another topic. Should I go to the phones? Yeah, let’s go to the phones. Let’s go to Josh in Boston. Hi, Josh. 


IRA FLATOW: Hi there. Go ahead. 

AUDIENCE: So my question is about food items that may have acquired some mold on them, such as maybe a piece of broccoli. And there’s only a small amount of mold on it. And if I was to take off that small amount of mold, is the rest of the vegetable good to eat? 

IRA FLATOW: Yeah, cheese has always had some mold growing on it somewhere when you keep it around. Yeah, that’s a good question. 

BRIAN SHELDON: This is Brian. Again, just because you don’t see it, doesn’t mean there’s not mold spores there. Most of the microorganisms, before they reach a certain population, they’re invisible, but they’re there. For the most part, though, most molds are not pathogenic to us. They’re not toxigenic to us. I suspect that those that are growing on the food are not. There are some molds, though, that produce toxins and [INAUDIBLE] toxins, et cetera, that are very toxic to humans. 

But for the most part, I would not presume that they would be on broccoli. But you know, washing, obviously, or cutting off the part of it, I’ve eaten many a moldy bread before because I could actually taste it. You couldn’t see it, but you can taste the mold in there and did perfectly fine with it. 

IRA FLATOW: Let me ask you the question about raw cookie dough. People love raw cookie dough. Is it OK to eat raw cookie dough? 

PAUL DAWSON: Well, the FDA and CDC warn against that. And then, I know, recently, there was an article by a fellow from the University of Michigan who actually is involved in the health field, saying that– he didn’t say it was OK. It just kind of had a rhyme there. If you really enjoy it and you’re willing to take the risk, it’s up to you. But the fact of the matter is, there’s really two parts of that dough that can be dangerous. It’s the flour can contain and has contained in the past– found contaminated flour. 

And also, the eggs, if you use egg in the batter. So those can contain pathogens. Of course, they don’t always contain pathogens. So it’s an easy analogy, and the book is kind of like wearing a seat belt. You can eat raw cookie dough your whole life or never wear a seat belt your whole life, and if you don’t have an accent or don’t eat– don’t run into some cookie dough that’s contaminated, you’re going to be OK. But you hit the one that is, and you’re most likely going to get hurt. 

And there actually are some cookie doughs out there now that have been sold on the market that actually are safe to eat raw, that they’re made without eggs and also the heat– the flour is heat treated. So people who like to eat raw cookie dough, can go that route they so choose. So, again, it’s a matter of– you’re taking a chance. And if you have an option that guarantees you’re not going to get sick, I would not chance it. 

IRA FLATOW: Let me go to the phones to Adam in Chicago. Hi, Adam. 

AUDIENCE: Hi, this is Adam calling from Chicago. And I was wondering if it’s just as dangerous to do a waterfall, like when you just pour the drink in your mouth without actually touching it– sharing with your friends, if it’s just as dangerous to do that as it is actually drinking the beverage from the actual bottle or cup? 

IRA FLATOW: OK, Brian or– 

BRIAN SHELDON: I’m not sure I understood the question. Maybe Paul did. 

IRA FLATOW: Well, actually, you’re too old to understand that, actually. 

PAUL DAWSON: I think, if I understand the question, you have a squirt water bottle and, rather than put your lips on the bottle, you squirt it in your mouth. And I would say if you’re not contacting the bottle, and you’re also– there’s no chances– the word we use is “backwash–” you’re not contaminating the water in the bottle, so that is safer. 

And, yeah, sharing water bottles is highly frowned upon by the health industry and medical industry. And actually, I was reading as part of background that one of the soccer associations in, I think, New Zealand actually has a big problem with that. They have a warning of that. So that’s a good question. 

IRA FLATOW: Yeah. That’s why you see athletes at football games, they’re squirting it into their mouth without touching it from the bottle. Let’s talk about the ultimate holiday raw egg food, which is eggnog. Now if you spike the eggnog, does alcohol kill the bacteria in the eggnog? 

BRIAN SHELDON: Well, there’s been some studies done. And actually, I think a show appeared on your show a number of years ago, a microbiologist from Rockefeller University, he had made a batch of eggnog, which he had spiked with a salmonella test strain. And he refrigerated this for three weeks, and he measured the populations over that three-week period of time. And he saw that there was a reduction in the population and, ultimately, elimination of the organism after three weeks. 

Although, I would say that the Food and Drug Administration frowns upon that. They recommend that if you’re going to do– make an eggnog that’s spiked of alcohol, that they recommend that you start with a cooked egg bass beginning. In other words, if the recipe has milk in it, you take half that portion of milk, plus the egg, and you heat it, constantly stirring it up to 160 degrees Fahrenheit. And that should be sufficient, if salmonella is present, that you would have killed it. 

Then, you, essentially, allow that to refrigerate, to cool down, then you add the rest of the recipe to it– the milk, the sugar, the flavorings, et cetera. And the recommendation is that you should never count on the alcohol actually sterilizing the product. And again, back to that example of that study at Rockefeller University, that was three weeks sitting in the refrigerator. Who’s going to make eggnog and let it sit in three weeks before they start consuming it? This is usually made a day or two before the event. And you start drinking it immediately. 

IRA FLATOW: Yeah, speaking of salmonella, something that just popped into my mind that we hear all year but maybe should be emphasized again in this cooking season, and that is, never to wash the chicken before you use it, right? 

PAUL DAWSON: Right, that’s a good one. The reason being, you can aerosolized the salmonella, spread it around the kitchen, the sink, the counter. You’re going to cook it anyway, and you’re going to destroy– if cooked properly, you’ll destroy all the pathogens or salmonella on that product. So by washing it, you’re not really giving yourself any advantage. And secondly, there’s a good chance you’re spreading it around the kitchen. 

IRA FLATOW: Yeah, let me go to the phones. Let’s go to Amy in Manhattan. Hi, Amy. 


IRA FLATOW: Hi there. Go ahead. Amy, are you there? 

AUDIENCE: Sorry. Yeah, yeah. Sorry, I have a problem with my phone. Yeah, I was wondering on the double dipping, suppose you hold your chip or whatever you’re dipping in the middle and you dip each end– you know, dip one end, bite it off, and then dip the other end without moving your fingers. Does that make it safe? 

PAUL DAWSON: Well, yeah, except you’re actually– your hands now are what’s contaminated. You’re not getting oral bacter– that’s a good way to avoid the oral bacteria. But yeah, so I guess the hands are a real concern of the way bacteria is transferred as well. But yeah, that’s a way to avoid that. 

And I’m glad you asked that question. Because the one thing– one of the interesting things you found out on the double dipping was we actually used– we tested salsa, chocolate and cheese dip, and found there was more transferred to the salsa than there was to the cheese and chocolate. And we thought about this because it’s a thinner dip so more was falling back in there. 

And relative to the dill pickle question, actually, the salsa, we let the dip sit there two hours and actually saw a reduction in the number of bacteria in the salsa. But it was still there. So I guess to add onto the dill pickle question, it depends on how long in contact the bacteria is with the acidic environment. And even after two hours in the salsa, which is pretty low pH, it still wasn’t gone. 

IRA FLATOW: Let’s go to Merritt from Vail, Colorado. Hi, welcome to Science Friday. 

AUDIENCE: Hi, happy holidays. I love your show. 

IRA FLATOW: Thank you. 

AUDIENCE: I have a question for your expert based on a secret I’ve kept for years and years. My family always has really large Thanksgiving dinners. Tons of people around– and in the hustle and bustle of cleanup, my uncle put together a plate of this leftover scraps, a few things– took it outside and let his dogs have it, brought the plate back in, put it on the kitchen counter, and there was one lone piece of asparagus that the dog didn’t eat. And my grandmother, who hadn’t seen this, walked by, picked up the asparagus, and ate it. None of us ever told her. 

She’s no longer with us. The asparagus had something to do with that. But I was just wondering what your expert’s take on that was, that she just ate this asparagus. And in general, we have lots of cats and dogs around. People do all kinds of things that I think are kind of gross– feeding the dogs from the table, letting the cats walk around. So I just wondered about the introduction of pets into the– 

IRA FLATOW: Before we get that answer, let me remind everybody– because it’s going to be a long answer, I think– this is Science Friday from WNYC Studios, talking with Paul Dawson and Bryan Sheldon, authors of Did You Just Eat That? And go ahead, who wants to jump in on that one? 

BRIAN SHELDON: I hope the asparagus didn’t have anything to do with the passing of a relative. 

IRA FLATOW: Let’s assume it hasn’t. 


BRIAN SHELDON: No, I suspect it hasn’t. I go back to the original scenario that– Paul actually mentioned it, that we eat 365 days a year, three meals a day, if we’re lucky, and we don’t always get sick. And we have animals and pets. And we eat in, we eat out. 

But then, again, there is a risk associated with this. Again, dogs and cats, they appear to be clean. Obviously, they don’t wash their hands or their feet, their paws. And so consequently, there’s a greater risk that the organisms that they have on their paws or in their mouth are those things that they’ve picked up elsewhere that could very well be containing pathogens. There is a risk associated with it. How great that risk is, I don’t think any of us know. You could calculate something like that. But I suspect that there’d still be small. In the animal, it appeared to be clean. The surface can appear to be clean. But it has microorganisms on it. And it’s just a matter, are they pathogenic in nature? 

IRA FLATOW: Let me go to Richard in Fort Myers, Florida, because he has a question I have at least half a dozen people asking. Go ahead, Richard. 

AUDIENCE: Yes I have a question regarding toddlers and little kids in general running around, dropping food, picking up food, seeing something that they like, put it in their mouths, et cetera, et cetera. 


AUDIENCE: And along with that, I’m wondering if that doesn’t help them to build an immunity to organisms that may exist in that environment. 

IRA FLATOW: Let me get an answer to that. All these toddlers, they’re crawling on their four limbs, or they’re standing up, they’re picking up the food. Is this good? Should we stop them from doing this? 

PAUL DAWSON: Well, you probably can’t stop them, first of all. And certainly, it does help the immune system. And as Brian mentioned early on, I think, about the microbiome, there is a lot of research that the bacteria in our body and other microorganisms are very important to our health. That’s been well known, but there’s a little more being explored in that area. And certainly, exposure to bacteria and viruses at a young age helps build the immune system. 

And I guess the caveat to that would be that we all, as adults, experience that. And now, we have strong immune systems. There are some things that overwhelm the immune system in some cases, and we certainly don’t want to risk exposure that. But yeah, quick answer to that is, yes, it certainly does, I would say. 

IRA FLATOW: All right, we have run out of time– so much to talk about. I want to thank both of you– Paul Dawson, Professor of Food and Science at Clemson; Brian Sheldon, Professor Emeritus at North Carolina State University in Raleigh, the authors of the book Did You Just Eat That? Did You Just Eat– [LAUGHS]– it’s a great book. You can read an excerpt from the book on our website at sciencefriday.com. Thank you for joining us today.

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