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Relishing The Science Of The BBQ


This is SCIENCE FRIDAY. I'm Ira Flatow. Up next on our summer science issues that we'll continue. Joining me now is editor - multimedia editor Flora Lichtman. Hi, Flora.


FLATOW: Hi there.

LICHTMAN: That's right. You know how I love news you can use, and we have got more of it coming. It turns out that the grill pit is a hotbed of science. So a little later, just so you can get excited, we have a futuristic ketchup jar and the microbiology of pickles. But first, best practices for a pathogen-free picnic.

FLATOW: You mean, ah, the pathogens in potato salad and stuff like that.

LICHTMAN: Yeah. You might want to pass, but don't blame the mayonnaise it turns out. Here to clear mayo's name and to share other tips is Angela Fraser. Fraser is a professor and food safety specialist at Clemson University in South Carolina. Welcome to the show, Dr. Fraser.

DR. ANGELA FRASER: Thank you. Thank you. Appreciate being invited.

LICHTMAN: So let's start with the mayo. Does it get an unfairly bad rap when it comes to food poisoning and picnics?

FRASER: Yes, particularly commercially-prepared mayonnaise, so the mayonnaise you would go to the grocery store and buy, you know, either in a plastic container or in a glass jar. The pH or the acid level of the mayonnaise is so low that most pathogens will not grow in it.

LICHTMAN: Wow. So when people point to the chicken salad, that's not necessarily true?

FRASER: Well, it's when - when I'm talking about the pH of mayonnaise, I'm talking about the pH of mayonnaise in and of itself. But when you begin to mix the mayonnaise with other ingredients that have a higher pH, you alter the overall pH. And so the problem is, is when you're mixing what we would call low-acid foods, such as chicken, potatoes, pasta, lots of vegetables, with mayonnaise, you increase the pH. And then that type of a mixture if it's not held at proper temperatures can support the growth of, you know, pathogens that could make you sick.

LICHTMAN: OK. So you would still be wary but...




LICHTMAN: What about melons? They seem so harmless, but I read that that they can cause problems too.

FRASER: Yes. And there are some fruits that also have a high pH. Let me just briefly explain what is pH: pH is measured on a scale of zero to 14, and a neutral pH is seven. Most harmful bacteria cannot grow in what we call high-acid foods, so foods that have a pH of 4.6 or less. If the food has a pH of above 4.6 - and there's a way that you measure it - that food can potentially support the growth of harmful bacteria. And so melons and some other fruits have pH values of above 4.6, making them low-acid foods. Low-acid foods must be kept hot or cold, and so, obviously, you're not going to keep melons hot, therefore you need to keep them cold.

LICHTMAN: And don't leave them on the counter, right?

FRASER: Correct. And the general rule is, is you don't want to keep those types of foods on the countertop for more than four hours. And, you know, sometimes the mistake people make is that a food might be out on a countertop for four hours, and they'll say, oh, forgot it and let me just put it back into the refrigerator - no. Once a low-acid food - and we also call those potentially hazardous foods - are sitting out, you know, not under temperature control, after four hours, you need to either eat it up within four hours or throw it out.

LICHTMAN: Mm-hmm. And it's the rind, too, can pick up nasty bacteria.

FRASER: Yeah. Think about where, you know, you harvest a melon. It comes from the ground. I mean, bacteria are everywhere, and so bacteria in soil, in the air, on surfaces, et cetera. And so, you know, so the rind can become naturally contaminated, or it could become contaminated during the harvest process by the worker who's harvesting the melon or even during the cleaning process or in a grocery store. You know, there's a lot of research being done on how are melons becoming contaminated, and so there's still many unknown questions.

LICHTMAN: Mm-hmm. What about sugar? Does sugar make things inhospitable for bacteria to live in? Is that why people leave pies out?

FRASER: Well, another feature of what we would call a non-potentially hazardous food - and, again, a non-potentially hazardous food does not need to be kept under temperature control - is something called water activity. And so what that is is the amount of water that is available for these microorganisms to function. And when you add sugar or salt or some other substances to foods, you decrease - you potentially decrease the water activity of the food. So foods that have a high-sugar content generally have a lower water activity, and so harmful organisms cannot grow in that food, which is why some foods like some fruit pies, not all, can be left out at room temperature, and, you know, you don't worry about getting sick from eating that.

FLATOW: Mm-hmm.

LICHTMAN: And is it - what about public grills? Should we be wary?

FRASER: I personally would. You know, I...


FRASER: When I was checking the research to see if anybody has actually done a - performed a study, you know, where they've gone out and they've collected some samples, you know, surface sample, swab the surface of the public grill and determine, hey, what might be on the grill surface? And I could not locate any study that had been conducted.

And so my biggest concern is, you know, there's a lot - a lot of times, you see these public grills, there's just like a thick crust on the grills. You know, some of these pathogens might survive under that crust. We don't know. And so if you just fire it up and think that if, you know, letting the fire, you know, try to burn off whatever might be on that grill, that it would be safe, we don't know if that is true. And when I don't know if something is true, I err on the side of the caution.

And so what I would recommend is that you simply put like a clean piece of foil over the grill and then, you know, cut some holes in it, and put your meat or whatever you're grilling on top of the foil. That way, you don't have to worry.

LICHTMAN: I will never look at a public grill the same way.


FRASER: And who knows what other kind of substances might be on the grill? I mean, that's - I would be concerned about that as well, not just microorganisms.

LICHTMAN: Yeah. What about defrosting meats and stuff out of the fridge? I've heard both - it can go both ways on that. What's the real deal?

FRASER: Yeah. There is, you know, there are some people who deviate from the traditional recommendation. What I would recommend is that defrosting or thawing of raw meats, fish and poultry should be - should take place under what we would call temperature control. So it should take place in a refrigerator, during the cooking process or under cold, running water. Now, I typically don't advise consumers or anybody working in the food industry to use cold, running water because it's probably not a good use of resources because you'd have to let the water run for, generally, about 30 minutes. So thawing in the refrigerator or during the cooking process, which would include the microwave, would be the best way.

LICHTMAN: Do you have any other take-home tips for people who are barbecuing or picnicking this summer before we have to go?

FRASER: I would suggest that people prepare as much of their foods at home where they have access to water and a refrigerator. So if you're going to make hamburger patties, make the patties at home, you know, put them into a container and so that you minimize handling at the picnic site.

Another thing that I'd like to point out is, we checked the CDC data, and in the past 10 years, there has actually been 193 outbreaks attributed to foods that were prepared at a picnic. And these outbreaks sickened over 5,000 people. So it can happen.

LICHTMAN: Tread carefully.


FRASER: Tread carefully, exactly.

LICHTMAN: Well, thanks for joining us today, Dr. Fraser.

FRASER: OK. We have - I very appreciate it. Thank you so much.

LICHTMAN: Angela Fraser is a professor and food safety specialist at Clemson University in South Carolina.

FLATOW: Wow. That was interesting. I didn't realize all those pathogens - got to be careful. Well, what else have you got us for us?

LICHTMAN: The hidden trap of your picnic where...


FLATOW: Summer science, barbecue blowout continues.

LICHTMAN: It continues, and you're going to relish the next one, Ira.


LICHTMAN: Ooh, I know.


LICHTMAN: Engineers at MIT, who usually spend their time on trivial things like nuclear power plants and efficiency in wind turbine surfaces, have finally taken on a relevant problem, a condementory(ph) problem: the jammed ketchup bottle. In fact, their invention could turn this sound...

FLATOW: Hitting that bottle, right?

LICHTMAN: You know it well.


LICHTMAN: At least I do.


LICHTMAN: Into a relic of another time.

FLATOW: Hmm, like the busy signal or the dial-up modem that I...

LICHTMAN: Yeah, exactly.


FLATOW: Kripa Varanasi, a mechanical engineer at MIT in Cambridge and his colleagues seemed to have solved this condiment conundrum. From their weekly glide jar, ketchup flows freely no matter how little is left. And he's here to tell us about it. Welcome to the program, Doctor Varanasi.

DR. KRIPA VARANASI: Thank you very much.

LICHTMAN: So, you know, I always thought that this is a ketchup problem, not a jar problem, but it sounds like maybe I was wrong.

VARANASI: Yeah. It's actually both, but the resistance to flow mainly comes from the interface between the ketchup and the jar. And by changing that interface using this new coating that we've developed, which is super slippery, we can get the ketchup to flow out of the jar very easily without sticking to it.

LICHTMAN: So give us the simple, thumbnail sketch. How does this coating work? What is it made of?

VARANASI: So the coating, is essentially - what we call it a structured liquid coating, so it has both a texture to it and a liquid that fills the texture.

FLATOW: Is there a way to think about this? Do you have an analogy? It's hard for me to imagine a solid liquid.

VARANASI: So if you - analogy that one of my graduate student uses is, you know, if you take gum out of, you know, gum and try to throw it out with your - with dry fingers, it wouldn't slide off, right? But if you have a - if you wet your fingers, then the fingers have a texture, and the liquid would wet those textures and then the gum slides off very easily. So it is a lubricant layer at the interface, right, that allows you to slide off anything very easily.

LICHTMAN: And how do you get it in the jar?

VARANASI: So we are developing various manufacturing processes, and one of them is a spray-based process, and so we spray on this coating on to the bottle.

LICHTMAN: And could it come off in the bottle and then assemble itself in your intestines?



VARANASI: We wouldn't want that to happen.

LICHTMAN: No, indeed.

VARANASI: So the coating, preferentially, actually self-assembles on the jar and wouldn't come off into the food.

FLATOW: And the ketchup just slips right out of the jar without having to hit it.

VARANASI: Exactly.

LICHTMAN: And does it work on others - does it work on anything you put in that jar?

VARANASI: Yes, so...

LICHTMAN: What about something stickier, like peanut butter?

VARANASI: Yes. So we - so what we are trying to do, the engineering - so this coating can be engineered for a different application. So it could be engineered for, you know, things like mayonnaise, which are very hard to get out. And we have some demo videos that we have that were in the news. We have - you can engineer this to slide ice, you know, for applications like deicing on aircraft engines or wind turbines or power lines. It could be applied to things like droplets that need to be shed in condenser tubes in power plants, even cosmetics. For example, you know, you have an expensive lotion...

LICHTMAN: Let me just interrupt you for a second and let everybody know that this is SCIENCE FRIDAY on NPR.

VARANASI: Yes. So...

LICHTMAN: I'm Flora Lichtman.

FLATOW: I'm Ira Flatow here.

LICHTMAN: And we are just about out of time, but one last question. What is the coating made of?

VARANASI: So the coating, like I said, can be engineered out of different materials. For the ketchup bottle stuff, we use food-based materials.

LICHTMAN: So proprietary, I guess, is the...


VARANASI: Proprietary at the point, at the minute, yeah.

LICHTMAN: Thank you, Doctor Varanasi for taking time to be us. This is fascinating, and I know your other work is on other surfaces. So we'll have to keep after that, too, right?



LICHTMAN: Doctor...

VARANASI: Thank you very much.

LICHTMAN: Thank you. Dr. Varanasi is a mechanical engineer at MIT.

FLATOW: All right. So he has covered ketchup and mayo. What's next on our barbecue...

LICHTMAN: Well, you might think it's mustard...

FLATOW: Of course.

LICHTMAN: ...but it's not. It's the pickle.

FLATOW: The pick, my favorite.

LICHTMAN: It's the pickle of the week, and it might be the pickle of every week because I - it turns out, I love pickle science. I didn't know this, but there are multiple kinds of pickles.

FLATOW: Right.

LICHTMAN: So there's the salt brine, sort of fresh pickle, I found out from fermentation expert Bob Hutkins. But there are also pickles that are fermented. So enlist bacteria to do the job for you, basically.

FLATOW: You have to put bacteria into the pickle jar.

LICHTMAN: It turns out that you do not have to put bacteria in, they come with, but it's a good question because they're not the only ones on the cucumber to begin with. Here's Bob Hutkins.

BOB HUTKINS: The bacteria that surround that cucumber are quite diverse, and many of them, in fact, most of them are really not the ones that we want to grow. The lactic acid bacteria are probably outnumbered by 1,000 to one or even more by undesirable bacteria that would otherwise spoil that cucumber.

So what's done is to apply this salt brine, and that salt brine, in large part, will inhibit those undesirable organisms. And they create what we call a selective environment promoting the growth of salt-tolerant lactic acid bacteria.

LICHTMAN: So it's amazing. Like in every cucumber, there's this microbiological war going on in the beginning. And, you know, we help them by creating this sort of salty environment that only the, you know, from our perspective, the good bacteria can live in.

So what occurred to me is, you know, why are these bacteria safe for us, whereas other bacteria make us sick?

FLATOW: Right.

LICHTMAN: And it turns out to be a really interesting story.

HUTKINS: You know, over the course of evolution, and let's face it, these bacteria have been around a lot longer than we have, there are some lactic acid bacteria that have even the vestiges, the genetic remnants of virulence genes, i.e., genes that at one time may have been responsible for causing disease, but these bacteria have been more or less domesticated. So there is some notion that there is co-evolution that the bacteria that are associated, for example with the healthy gut, have co-evolved with human kind and have become specialized in that environment. Good for us.

LICHTMAN: The domesticated bacteria.

FLATOW: There you go, making pickles.

LICHTMAN: And we - you can make them.

FLATOW: You can make them at home.

LICHTMAN: It turns out, yeah. I asked Bob Hutkins, and he gave us a little recipe with the caveat that he actually hasn't made them.


LICHTMAN: He says it's really easy and you...

FLATOW: You tried this at home (unintelligible).

LICHTMAN: Exactly, or you can go to our website and look at how to do it. It's pretty simple. You just put them in a salt brine, and you have to get the brine right and the weight right, but...

FLATOW: Mm-hmm. Some people put them out in the sun. I remember seeing people put them in the jar, they put them out in the sun in the backyard?

LICHTMAN: Yeah. Apparently, there is some evidence that the sun helps combat the other bad bacteria. In fact, I read that even industrial makers put them in these vats, but Hutkins said that they're usually closed. You want to keep the other stuff out.

FLATOW: All right, Flora. Thank you very much.


FLATOW: Everything you wanted to know about barbecue science this hour, Flora Lichtman, our multimedia editor, and he(ph) was interviewing Bob Hutkins. Transcript provided by NPR, Copyright NPR.

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