Ice Cream Science

Air Date: 07/05/2006
Scientific American
Science Talk
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In this 2006 Scientific American "Science Talk" interview, two food scientists and researchers from Ben and Jerry's in Vermont explain the chemistry of ice cream, a "frozen aerated dessert" that is a three-phase emulsion: a liquid, gas and solid all at once. Source: Scientific American, July 5, 2006

Ice Cream Science

In this episode, we go to the research and development facility of Ben and Jerry's in Vermont, to talk about the science of ice cream. We'll talk to Derek Spors, ice cream scientician (a.k.a. "senior product developer-food technology") and Eric Fredette, group leader of flavor development. Plus, we'll test your knowledge about some recent science in the news.

Science Talk July 5, 2006 -- Ice Cream Science

Welcome to Science Talk, the podcast of Scientific American for the seven days starting July 5th. I am Steve Mirsky. This week on the podcast, the science of ice cream. I was in Vermont last week and on June 30th I visited Ben and Jerry's research and development center. They call R&D bizarre and D, by the way, in South Burlington, Vermont. I didn't talk to Ben and Jerry; I spoke with Derek and Eric as you'll hear. Plus, we will test your knowledge about some recent science in the news. And now some really cool stuff—ice cream.

Steve: I'm here at Ben and Jerry's. And who are you?

Derek: My name is Derek Spors. I am an ice cream scientician.

Steve: And, what does that mean? What's your background?

Derek: My background is food science. I have a degree from the University of Wisconsin and it's basically looking at the chemistry, bacteriology, and a little bit of engineering as it all relates to food.

Steve: That's of foods. It's a degree in food science.

Derek: Yep.

Steve: And, who are you?

Eric: My name is Eric Fredette, and I am a novelteer here at Ben and Jerry's.

Steve: A what?

Eric: A novelteer. I work on anything that is not in a pint. So, a stick bar or an ice cream sandwich that type of thing. Those are called ice cream novelties.

Steve: Cool. Derek, what is ice cream?

Derek: Ice cream in its boring generic definition would be a frozen, aerated dessert, which is a blend of dairy, butterfat, sugar some other fillers and flavoring.

Steve: Is it in an emulsion? Is it a slurry? Is it a solid? Is it a liquid? I know it's not a gas, but I can't figure out what else it is.

Derek: Well, actually it's all of those things. It starts off as [a] liquid mix. There are government regulations as to what constitutes ice cream. You have to have a certain level of total milk solids, as we call them. You have to have a certain level of milk fat. You have to have a certain weight per gallon. There's a lot of little rules about it, but it starts off as a liquid blend of cream, milk, sugar, egg yolk, stabilizers, and that is frozen and air is injected when it's frozen. So, it's actually a fat and water liquid that is then turned into a three-phase emulsion when we add air to it.

Steve: A three-phase emulsion—so it's liquid, gas, and solid all at once.

Derek: It is, because you would never have all of your water frozen; even at any temperature, there is some liquid phase though that's still moving around because the whole thing doesn't reach the glossy state. There are certainly frozen ice particles and there are air cells as well.

Steve: What difference does it make what temperature I eat my ice cream at?

Derek: What temperature you eat it at doesn't matter a whole lot [except] for preference. What temperatures we produce it at, ship it at and store it at do make a big difference.

Steve: Tell me more about that.

Derek: When you make ice cream, you are creating ice crystals. The only place that you actually create ice crystals is in the ice cream freezer. Everything that happens to the ice cream after that only makes the ice crystals bigger. The amount of ice crystals you form is dependent on the formulation of the ice cream—how much water you have in there and what’s your freezing point is at. So, the colder we freeze it out of our freezers, the more ice crystals we form. That seems counterintuitive, but we actually want to have as many ice crystals as possible, because the more we have, then the average size is much smaller. You are going to have ice crystals in your ice cream because it's mostly water and it's frozen. So, our goal is to keep them as many as possible and as small as possible.

Steve: Because the bigger ones change the consistency.

Derek: Once they get to a certain size, they are detectable on your tongue and that's when you have coarser icy ice cream.

Steve: So, for smoothness you want a lot of little ice crystals.

Derek: Right, and as the product becomes abused as the temperature rises up, the smaller ice crystals will melt, when it cools back down they don't refreeze into their own ice crystal, because they’re only formed in the freezer. They will refreeze to a bigger existing ice crystal that hadn't melted already. So, this is called Oswald ripening. The small crystals get smaller and the big crystals get bigger.

Steve: And, this is what happens at home when you have taken the container out and put it back in the freezer a bunch of times.

Derek: Exactly, the container that you leave sitting o[i]n your refrigerator or on your freezer door, it's kind of [the] wors[t]e spot to keep ice cream because it has air rushing by it every time you open and close it. It has great heat transfer. It's the warmest part of your freezer. So, every time you warm it up, you are melting some of your smaller ice crystals; when you freeze it back down it's not refreezing into its own [crystal], it’s attaching to a bigger one.

Steve: So, you should put the ice cream deep in the freezer at home.

Derek: If you want to keep it for a long time. Fortunately [our] ice comes in a pipe[nt] and I don't think many people get more than one serving out of it. So, ours is pretty safe. But if you buy in a big container, the colder you can keep it, the longer it will last.

Steve: I was onto[under] the impression that the temperature that ice cream was served at would affects its taste, because of the volatility of some of the oils in there, but ...

Derek: It will have some impact. It's really more personal preference though. Ice cream being so cold, you don't get a lot of difference for it as [far as] volatil[ity is concerned]e is coming off. Ice cream isn't a product that smells a lot. Th[ough it]at does certainly have some smell to it.

Steve: Because of so much of what we think of this taste is related to smell. You are probably the right guy to talk about that. This is Eric.

Eric: Yes, the taste, your olfactory plays a huge part in taste because of the way your buds and everything are set up; and it's really that you smell something first, usually before you taste as you lift it [to] your mouth. So, absolutely smell ha[i]s a huge part of tasting, especially a stronger flavor of ice cream or something. Strawberry—you'll smell it first before you get it to your mouth, blueberry [too].

Steve: Since it's all so cold anyway, it's not [that] you don't have the same factor for smell as you would in room temperature for hot foods.

Derek: No, and in even something as volatile as vanilla—when you're talking about the difference of maybe certainly at 0 degrees Fahrenheit versus 10 degrees Fahrenheit, you are not really giving off a lot more vapor pressure for you to be able to smell it more where your olfactory comes in for ice cream as when it starts to melt in your mouth and it kind of gets kicked up into your nasal passages; and then the smell plays more of a factor.

Steve: What are some of the more interesting scientific challenges that you have in producing ice cream?

Derek: Well, I think, where you run into the most problems is when you are trying to take something out of ice cream. If you are just starting with a whole lot of cream, a whole lot of milk, a little bit of sugar and some egg yolks, like a regular product—that's really in its[a] scientist['s] dream to work on because everything is very well balanced such as it works itself out. Now, let's say you want to take carbohydrates out of an ice cream—a low-carb ice cream, then you have some big challenges, because you have to have a certain amount of total solids to have the right mouth feel and you also need to have the right freezing point depressant. So, carbohydrates tend to be kind of simple, smaller molecules that will depress the freezing point a whole lot more. than they get a large fiber molecule. By taking all of those out, I really need to drop the freezing point somehow. So, I need to find things that aren't carbohydrates that have tiny molecular weights to really drop that freezing point down. Those we[a]re the [things]times that are most difficult to work with.

Steve: So, small proteins—what do you put in there instead?

Derek: Sugar alcohols had[is] a primary one—things like sorbitol or glycerin. Glycerin is the most popular, because it's only about [a] molecular weight [o]f I think around 99, where your average sucrose molecule will have about 342 for a molecular weight. So, you get a little more than three times the freezing point depressant that of[from] glycerin as you would with sugar on a pound-from-pound basis.

Steve: Right, because the freezing point is a function of just the number of particles.

Derek: Right, the number of molecules. So, it's not about the mass that goes in, it's the number of molecules. So, the smaller molecular weight for a single pound, you're going to add a lot more to it. This will also create a whole bunch of other issues with low-carb ice creams because sugar alcohols tend to have a very positive or negative heat-up solution, so glycerin has a very positive heat-up solution. If you add too much to it, you get what's called glycerin burn and your tongue will actually start to warm up. So, then you need to balance that out with something with a negative heat-up solution like sorbitol I[has]s a very negative heat-up solution. So, by combining the right combination of glycerin and sorbitol, I get my freezing point right and my heat-up solution correct.

Steve: V[W]ow, that's the most interesting thing from [a]besides different point of view about ice cream, however.

Derek: It can get pretty in depth.

Steve: Heat-up solution—explain that a little bit.

Derek: Heat-up solution is basically—in the most basic sense would be—doesn't make your mouth feel warm or cold. Things like if you are to eat a mint and it has a very cooling effect on your mouth that's something that has a negative heat-up solution. As the particles come into solution it has a cooling effect on your mouth.

Steve: As a novelteer, tell me about your background—you have a serious food background.

Eric: My degree is in culinary arts. So yeah, I have a food background. I have worked in restaurants and hotels in the Boston area and around Burlington here where we live.

Steve: This is Eric by the way. That was Derek. This is Eric. It's not a British comedy act, its Eric and Derek at Ben and Jerry’s. So, tell me more about it.

Eric: Sometimes it is a comedy.

Steve: Sometimes it should be comedy. I had the Key Lime pie, the new flavor the other night. Did you [help]have developed that?

Eric: I did.

Steve: Because I am a big Key Lime pie guy, and that it's excellent, it really is.

Eric: And, the big thing about the Key Lime pie is the variant—the swirl in that ice cream is lime curd, which is so close to the filling of an actual Key Lime pie. The ingredients are very similar—egg yolks, cream, lime juice; and by [swirling]slowing that in and putting pie pieces in, it creates the experience. It's exactly how you remember Key Lime pie to be when you eat it.

Steve: What's the challenge for you in trying to do something like that? There are obviously going to be places where you cannot use the same materials because it might have been something that was in a hot food—or I don't know if that's an example and just that's off the top of my head—but you have challenges to kind of recreate a taste in ice cream where ice cream is not the original kind of home for that taste. So, what kind of challenges [do ]you face there?

Eric: One of the challenges that we face—and [can] you have Derek talk about [it]—[is] balanc[ing]e in the mix and[of] solids and fats and all that. One of the challenges is adding things to the basic mix that have sugar in them. It throws off the balance of the finished product. So, some items will heat shock better than others. If you add a lot of sugar—if you add caramel to the background of an ice cream—you are adding a bunch of sugar, which throws the balance off, which means every time you open and close that freezer door, your ice crystals are more likely to get bigger faster than even a vanilla ice cream where you are not adding sugar to the base mix.

Steve: Heat shock has a very specific meaning in biology. I don't think it has the same meaning here. What does it mean when you use it?

Eric: Heat shock for us is every time the ice cream warms up and refreezes. So, it's a shock when you open the freezer door, when it's sitting on the counter, when you put it in the microwave— we are up, everyone has done it—you know, that creates an instant heat to the ice cream; and then you refreeze it and that's how[what] we consider heat shock.

Steve: So, impatience is a really bad idea for ice cream consumers.

Eric: Yes.

Steve: Let it warm up a little naturally.

Eric: Right. If we[you] can put it o[ff],n just leave it on the counter for a few minutes.

Steve: Is it possibl[e] for [you] yourself to do that?

Eric: Hold out—it's better that way.

Steve: Another serving of ice cream science right after this.

For breaking news about science and technology, visit today.

Steve: I know sometimes in New York, we pull pints of ice cream out of convenient[ce] store freezers that have been in there, I think since mammoths, were licking them in the first place. It has been very cold for, you know, it has been in there for six months. Is that going to matter at all?

Eric: It matters. It depends on the cycle of the freezer. So, if the freezer is on a cycle where it defrosts three or four times a day, that causes heat shock to the product. In a storage freezer like our facility, we store it –minus 20 [degrees]. So, it keeps an even temperature. It's always minus 20. We can keep ice cream; we eat ice cream a year-and-a-half after its manufacture. If it's kept at minus 20, it's still good.

Steve: [minus] 20 Centigrade or Fahrenheit?

Eric: Fahrenheit.

Steve: Okay. Now going back to Derek.

Derek: We test all of our products. We have what's called an environmental chamber that has a real basic temperature fluctuation program on it. So, in about two weeks we can simulate about one year of shelf life for the finished products through normal distribution. But it's, you know, the year is dependent on what type of temperatures it's exposed to. So, if you have something that's completely melted down and then refrozen, its shelf life is about a week. Where you can have—like Eric said, if it's temperature is very cold, you don't have a lot of ice crystals melting and refreezing—it can last for years.

Steve: What's going on when I pull out a pint of ice cream—I am lying, when I pull out a half-gallon of ice cream—from my freezer at home, and I open it up and it has been in there for a while, and I have got these ice crystals that have just grown all over the thing? Now, that's obviously more than just a consolidation of the little ice crystals that were in there. So, it's picking up moisture from inside the freezer and adding that to the crystallization?

Derek: It could be adding some to it, but a lot of it—in fact most of it—probably is from the product. If ice cream is 38 to 42 percent solids, that means it's almost 60 percent water. So, you have a lot of water in ice cream. All of the ingredients—milk, the main ingredient [in] milk is water, [the] main ingredient of cream is water. So, everything that we are adding, it's primarily water. So, there's an awful lot of ice that you can grow in there.

Steve: So, I am drawing the water out of the mix, and it's forming these ice crystals that are at the top of the container.

Derek: Yeah, and some of, you know, evaporation occurs at any temperature; so some of it—if you have eaten down a little bit and you have sealed the top back up, you have a small amount of head space there—tha[n]t some of that water can actually evaporate from the mix. So, you can dehydrate the ice cream a little bit and then it can find a great nucleation site on the lid where an ice crystal can attach; and once the ice crystal attaches and starts growing, it just gets bigger and bigger and bigger, and that's where you get the knife-like crystals.

Steve: Now, whenever Derek, the food science guy started to get really technical, Eric, the culinary guy was on the verge of cracking up. I figured that in itself, was kind of interesting, and I asked him about his reactions.

You are greatly amused by the scientific jargon.

Eric: Yes, this is about the point where the geek alert goes off in the kitchen because it's the culinary side and the science side are so different; and it's very amusing to most of us every time Derek goes into the geek mode. And we understand how it works and we so appreciate his expertise, but it's just it's...

Steve:'s funny from the other side.

Eric: Yeah. I mean, when I have a baked piece that I need to make sure that the sugar in it is the right amount of sugar so it doesn't absorb too much moisture from the ice cream during migration and in the freezing process or in the storage process, you ask Derek; because you need to know, like, so how is this going to react in six months?

Steve: So, Derek, you are in a unique position. You are the gifted, but misunderstood brother in this operation. Is that about it? You are the smart guy that people aren't sure what you actually do, but they know what's important and whats [it's] worth.

Derek: Yeah, that might be the case. You know, I have the added benefit of I can talk my way out of a lot of things just by you know, start[ing] [to] dropping words like nucleation and things like that. And then I can start to see the marketers and things like that start to glaze over a little bit; and then, they['re] like, alright he's going off onto something in little geek land there, and I am just going to smile and nod. And that gives me a nice advantage.

Steve: Derek, you have found your home. We are geek land. Welcome.

Derek: It's great to do this interview. It's not often I get to do one or I get to, you know...

Eric: ...say nucleation and no one laughs.

Derek: Exactly; yes.

Steve: What's—for both of you actually, we don't have to talk specifically about Ben and Jerry because this is truth throughout the ice cream world—what makes some ice cream better than other ice cream? Does it really boil down to fat content, if you can boil anything in ice cream?

Eric: On the corner[culinary] side, fat is good. Fat carries flavors. It works for me.

Derek: And it also gives you a mouth feel for your product. You are required to—to call it ice cream, the FDA says, you have to have at least 10 percent of your product by weight has to be butterfat. So, that's the bare minimum [for it to be] called ice cream. We would like to go kind of above and beyond that; and it gives you a rich—besides just the flavor—it gives you a great mouth feel to it too.

Steve: So, you have regular ice cream, premium ice cream, super-premium ice cream. I thought it was all just how much fat is in the ice cream. Is that right? Is it more than that?

Eric: It is. It's what maybe not in the ice cream, it's what there is more off in the ice cream. Your supermarket ice creams probably have a lot more air in them than at super-premium ice cream.

Steve: You can tell that sometimes—you pick up two pints of ice cream, one is three times heavier than the other. It feels that way.

Eric: Exactly, and ours is usually on the heavy end because we have less air—it's more dense, it takes longer to soften when you pull it out of the freezer; whereas a half-gallon of supermarket ice cream, you can put a scoop in it the second you pull it out. It has lot of air in it, probably not a lot of add-ins. We would like to put in tons of big chunks. You get the same type of flavor in the supermarket ice cream, just not all the big chunks, not all the big swirl patterns, you know? You don't get as much fudge.

Steve: But typically, the premium ice creams will have a higher fat content because they have less air. So, by volume it will be more fat.

Eric: And probably a higher fat in the base mix itself.

Steve: In the base mix, okay. Derek, you have two brothers who do the same kind of thing as you do.

Derek: Yes, I do. A[I']m the middle child, and both my elder brother and younger brother are food scientists. They both went to Madison like I did, and they both work for our sister company in Green Bay, Good Humor-Breyers. Both in the R&D group as well.

Steve: So, what's [a] family reunion is like in your house?

Derek: You know, when everybody comes for Thanksgiving, everyone's got a thermometer to check the temperature of the turkey.

Eric: Once again, the geek alert goes on.


Steve: By the way, everyone who works at Ben and Jerry's can take home three pints of ice cream every day. They also have access to the free onsite gym.

Now it's time to play TOTALL.......Y BOGUS. Here are four science stories. Only three are true. See if you know which story is TOTALL.......Y BOGUS.

Story number 1: People who take their medicine regularly have a lower risk of death even if they are just taking a placebo.

Story number 2: Although men and women have equal online abilities, women rate their own talents for using the Web is being lower than men rate their abilities.

Story number 3: Researchers announce that they have catalogued all existing species of bacteria in what is left of the Atlantic forest of Brazil.

Story number 4: An asteroid thought to be about 400-meters across came almost as close to Earth as the moon is just after midnight Eastern Time in the U.S. on Monday.

And your time is up.

Story number 1 is true. People who adhere to their medication schedule have a lower risk of death even if they are only taking placebos. That's according to a study in a British medical journal. Regular adherence to one's meds is probably a marker for healthy behavior in general.

Story number 2 is true. Women think they are poor at online skills than men do, even though they have about the same skill level. The study is in the current issue of Social Science Quarterly. You can find it online at, well, I don't need to tell you, you can find it.

Story number 4 is true. A decent-size asteroid dubbed 2004XP14 did come within about 270,000 miles of Earth early Monday morning, Eastern Time. It was big enough to be visible through home telescopes, although it was probably tough to hone in on moving at 11 miles a second.

All of which means that story number 3—about researchers completing their survey of Atlantic forest bacteria in Brazil—is TOTALL.......Y BOGUS; because what is true is that a research team announced in the journal Science that they estimate that probably about 13 million species of bacteria still unknown to science are living in the Atlantic forest of Brazil. The forest is down to 8[percent] of the size it was 400 years ago. Each species of bacteria may have unique biochemistry that might be of interest in agriculture or pharmacology. You can read more in Tracy Staedter's article on our Web site, We will be right back.

John: Hi, I am John Rennie, editor in chief of Scientific American. Our magazine is now available in a digital edition. Not only does your Scientific American digital subscription include the full contents of every new printed issue, it also entitles you to access our digital archives from 1993 to the present. For more information, visit

Steve: By the way, I was a guest on the June 21st edition of The Skeptic’s Guide Into the Universe—that's the podcast of the New England Skeptical Society—and you can check it out at Well, that's it for this edition of the Scientific American podcast. Our e-mail address is; and also remember that science news is updated daily on the Scientific American Web site, For Science Talk, the podcast of Scientific American, I am Steve Mirsky. Thanks for clicking on us.

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