JOE PALCA, host:
From NPR News this Talk of the Nation Science Friday, I'm Joe Palca. For the rest of this hour we'll be talking about beer, but not just any beer. We're going to talk about crisp lager beer. Now this refreshing beverage doesn't go as far back as the wines of the Romans or the ales of Charlemagne's time. Experts say lager didn't bubble up until the middle ages, and that's because it's not brewed like wines or ales. Cool brewing lager beer takes a whole different yeast. My next guest has been using modern technology to take a closer look at that lager yeast, research that gives us a better idea of its history, and it might even help modern brewers develop better recipes.
Joining me now is Gavin Sherlock, he's an assistant professor in the Department of Genetics at Stamford University School of Medicine in Palo Alto, California. Welcome to the program, Dr. Sherlock.
Dr. GAVIN SHERLOCK (Assistant Professor, Department of Genetics, Stamford University): Thank you for having me.
PALCA: And if you'd like to join our conversation, give us a call, the number is 800-989-8255, that's 800-989-TALK. And I guess the first question would be, I mean OK, was it beer that drove you to yeast or yeast that drove you to beer.
Dr. SHERLOCK: Well, a little bit of both, but my lab uses yeast as a model organism for studying evolution, and in this respect lager yeast presented a really interesting opportunity to look at the evolutionary history and very recent evolutionary history of the lager yeast itself.
PALCA: I see. May - I mean, there's two ways to start, we can start about the genetics or we can start about the beer, and since it's probably a broader interest let's at least start a little bit about beer. What is the role of yeast in brewing beer?
Dr. SHERLOCK: So, yeast is capable of fermenting sugars to alcohol, and that's, you know, the main job it has either in lager, or ale, or wine making. But in addition has a lot of secondary metabolism where a lot of compounds that are present in the fermentation will be converted into other compounds that then impart flavors to the particular beverage.
PALCA: So, it's both alcohol and taste?
Dr. SHERLOCK: Yes, most definitely.
PALCA: And so, what is the difference then, between the beer that - I mean say the yeast that you used to make an ale versus the yeast that you used to make a lager?
Dr. SHERLOCK: So, the ale yeast is the normal species that used that we know about called Saccharomyces cerevisiae, which is also the same species used for baking and for wine making as well. The lager yeast on the other hand is a hybrid between two different yeast species and in the same way that a mule is a hybrid between a horse and donkey. The lager yeast is a hybrid between Saccharomyces cerevisiae and then another yeast called Saccharomyces bayanus.
PALCA: And how did this hybrid come about or maybe the other question is when did it come about?
Dr. SHERLOCK: So, lager brewing itself probably arose late in the middle ages. So probably sometime in the 1400's. So, these two differently yeast species are able to mate with one another to produce these hybrids , so the most likely explanation for what happened is that these two yeasts happened to be co-resident in a place where they were brewing ales and mated, and then I guess the monks or whoever was making the ale discovered that they were getting a new type of beer and so they would have selected for this yeast . And this yeast would have been the lager yeast, which is this hybrid.
PALCA: And I'm just, I mean, is there a difference in the amount of sugar that the different yeasts can convert? I mean is there a more alcoholic lager than ale or are they both limited to about a few percent?
Dr. SHERLOCK: They both tend to be a few percent, probably slightly less alcohol in the lagers than in the ales. One of the key differences is that lager is brewed at cooler temperatures, and that's one of the reasons why you end up with a very different flavor, because you get less of these molecules called esters and less of these fusal alcohols that you find in ales. So, lager has this kind of much more clean and crisp taste and aroma.
PALCA: So, what's the genetic signature of this mating that took place in three, two or 300 years ago or 400 years ago?
Dr. SHERLOCK: So, what we did was to try to take a number of existing lager strains and look to see which part of the original parental genomes that they still have resident within them. To do this we used something called micro rays, and you can think of this as like a glass microscope slide, but it has in our case about 12,000 spots on it. And each spot contains a tiny piece of DNA corresponding to a particular location in one of those two genomes. And then, we take the DNA from a given lager yeast, we label it with a red dye, put it on to this microarray. And then those spots which turned red will allow us to determine which sequences were present. And so, we did this for 17 different lager strains, and when we looked at the data, it was striking that they split into two quite clearly distinct groups. Some of them seemed to contain nearly all of the service biomes genomes where as the first group contains maybe all of the biomes genomes, but it's lost a lot of the service of (unintelligible) genomes.
PALCA: Mm hmm. Interesting and is the - well, is the yeast that is being used today is similar to the one that was - that was first arose when this new species arose?
Dr. SHERLOCK: It's difficult to know how much it has changed over there. I guess, probably five or 600 years since that arose. So, we - so at firstly, we believe that there was actually probably two origins of lager yeast. The results then were what we observed was these two distinct groups, and it's difficult to know how similar to the original kind of hybrid that was generated 600 or so years ago the present strains are. We suspected that that over the past 600 years, they've lost some genes from some of the genomes, which probably reflects selections by the brewers for yeast that they particularly like to the beer that was produced from them.
PALCA: OK. Our number is 800-989-8255, that's 800-989-TALK, and we're talking about the genetics and the taste, I guess I suppose. But the genetics of yeast and the taste of yeast or the least the beer that yeast make, and we're taking your calls on this and let's take a call now from David in Nashville, Tennessee. David, welcome to the program.
DAVID (Caller): Yes. That's a pretty fascinating subject. Something I learned in biology class was that the yeast organism never dies. Can you verify that or not?
PALCA: Mm hmm. Question.
Dr. SHERLOCK: So, yeast must certainly does die. So, yeast can divide both asexually as well as sexually and their - the typical mode by which there the dividing in a fermentation vessel is asexually, however an individual yeast cell although, it buds off new cells has the ability to divide, you know, only limited number of times. So if the yeast cells get older they get larger. They're kind of less able to metabolize and then probably after, you know, less than two dozen generation if they eventually die though.
PALCA: Mm hmm.
Dr. SHERLOCK: No, they don't live forever.
PALCA: So, David there. I think that means you have to go back to your biology teacher and...
DAVID: Yeah, but he still explained that - that still because in the survival for, you know, to connect the humans, you know, living a 150, 175 years, you know maybe a 100 years from now that they - they've done a lot of studies on the yeast organism because of that reason, speaking not forever. But, you have to admit that's a lot, you know, that's a lot of - a lot of generations so.
PALCA: Possibly so, well, maybe, maybe, maybe, they have something to learn about - to teach us about longevity. Let's take another call now and this time we'll go to Matt in Golden Colorado. Huh, that's a place for beer, Golden - Matt in Golden, Colorado. Welcome to Science Friday.
MATT (Caller): Hi. Thanks. Yeah. My question I guess is similar to Dave's. I just heard recently about the amber that they were able to extract yeast from. And how did they know that they had a strain that would be able to produce beer out of that?
PALCA: Yeah. I think I missed the story, but maybe Gavin Sherlock knows about it.
Dr. SHERLOCK: I do. There's a company called Fossil Fuels Brewing Company and they identified an insect embedded in amber and within its guts they were able to find the yeast, which they've been able to brew beer from. They proposed that this yeast may actually be an ancient, ancient yeast rather than a modern contaminant. And actually, I would be enormously interested to do some micro re-analysis on that yeast.
Dr. SHERLOCK: If anyone from that company is listening, we'll be happy to look at it for them.
PALCA: Wow, that's - that's great. Well, maybe we make the connection for you. But, so - so, but the ideas that you will only need one or two cells from this yeast in order to restore the population because since they've split asexually you could - you could grow them out.
Dr. SHERLOCK: Exactly. You can generate populations of millions of yeast in a very short amount of time.
PALCA: All right, interesting. Let's take another call now and go to Ken in Cleveland, Ohio. Ken, welcome to Science Friday.
KEN (Caller): Hi. Thanks. Good program.
PALCA: Sure. Uh huh.
KEN: Yeah. I had a couple of questions. One is how do - I mean, basically all yeast comes from the wild, OK. I mean, from the air. Originally, there's yeast and spores and everything all around us, and it comes from there. Now, when beer yeast or other kinds of yeasts are cultivated how do they separate out? How did they tell that the good yeast from the bad? The second question is what - how good of a microscope or what kind of a microscope would you need to actually see yeast cells and be able to see, well, here's a good yeast cell and here's - here's one I don't want.
PALCA: OK, interesting. Thanks for that, Ken. What about that? How do you keep your strains of yeast the way you want them to be?
Dr. SHERLOCK: So most industrial fermentations both for - for wine and brewing will use yeasts from a commercial vendors. So, you can buy - very similar to the way that you would buy Fleischmann's Yeast for baking, you can, pick a particular strain that maybe you like the characteristics of the drinks that it produces, and they'll send it to you and you add it to your fermentation. And you know, they use modern microbiological techniques to do that, and so it's going to be guaranteed to be a single type of yeast, which is the one that they - they advertise it as.
Now, in terms of distinguishing good yeast and bad yeast under the microscope, you really can't do it just by looking at them under the microscope. I mean, there's some small subtle morphological differences under the microscope where you really have to do some more specific tests either look at you know, what particular media they might grow what sugars they might be able use. Nowadays, we would probably offer some more kind of genomic-oriented technologies looking at some DNA sequences for instance.
PALCA: All right. We're talking about the genetics of yeast with Gavin Sherlock from the Stanford University School of Medicine. I'm Joe Palca, and this is Talk of The Nation from NPR News. So, does this work give you any ideas about how you might want to use - breed yeast to put - put certain trades into yeast that you might make for a better tasting beer?
Dr. SHERLOCK: Well, so one of the things about the lager yeast is being a hybrid yeast is that it's sterile. In the same way, that a mule is sterile. So, it's much harder to do genetics and so we can't, you know, do lots of mating experiments to generate a better lager yeast in that way. The other alternative would be for instance to recombinant DNA type strategy on it. So, that would be the introducing or deleting genes. I strongly doubt that the brewing industry is going to want to use genetically modified...
(Soundbite of laughter)
Dr. SHERLOCK: There's a lot...
PALCA: Franken-beer is that what you worried about?
Dr. SHERLOCK: It tastes well. It's just - I think there so much good beer out there.
PALCA: Uh huh.
Dr. SHERLOCK: That why would we even go down that road?
PALCA: Well, OK. I take your point. Let's take another call now from Isaac in, Rochester, New York. Isaac, welcome to Science Friday.
ISAAC(Caller): Hi. Thank you for taking my call. Look, very fascinating conversation. The question I want to go back to - your guest mentioned a while back that lager and yeast are lagers tend to have a lower, you know, about the same alcohol percentage content across the board. But, I've run into some in microbreweries that have had like 11 to 12 percent. I was just curious what your guest thought about that and I'll take my comments off the air. Thank you.
PALCA: OK. Thanks, Isaac. Yeah, what about that? I've seen that too.
Dr. SHERLOCK: So, so some obviously is - just like an arms race between brewers in terms who can produce the greatest amount of alcohol and the given beer. And it's possible to sometimes ago up to a very alcohol content, it depends on how much sugar is in the initial kind of liquor that's used for the fermentation, and then whether they have any additional secondary fermentations. But the typical brewers more like, you know, between the three and five percent.
PALCA: Mm hmm. So, how would I guess, so they could do it, but it would a more of an artificial situation rather than something they would make as a major production run (unintelligible).
Dr. SHERLOCK: Yes. I think so.
PALCA: I say. I guess, I should ask. I mean, have you a brewing background yourself or is this - are you strictly coming out as it is as a consumer and geneticist?
Dr. SHERLOCK: Other than a few brewing experiments in college, I would classify myself very much as a consumer.
PALCA: Uh huh. And then next the question and - since I can detect from your accent that you might have started on beer in a different part of the world. Care to jump in on the question of whether the lagers of America are better or worse than the lagers of Europe or in England?
Dr. SHERLOCK: I actually, don't drink so much lager. I'm more of an ale person. But if I drink lager, probably my favorite, actually, is an American, which is the Sierra Nevada Pale Ale. Sorry, that's an ale.
PALCA: Uh huh. Yeah.
Dr. SHERLOCK: Lagers, no I tend not to drink lagers. I certainly don't drink Budweiser or Miller or anything like that.
PALCA: I see. But, presumably I mean, so - I mean Budweiser and Miller they fight all the time about the various tastes that they have. But, is - are the yeasts the same or do they really have a different strain that they're dealing with?
Dr. SHERLOCK: For the most part, modern breweries I think they have very similar strains, although I don't think you can just ask them for their strain for analysis. I think they're quite propriety about it.
Dr. SHERLOCK: I think the major determinant is going to be what they actually put into the fermentation.
Dr. SHERLOCK: And then, you know, maybe some small differences in their actual process.
PALCA: Got it. OK. Let's take another call now and this time go to Dan in Hartford, Connecticut. Dan, welcome to Science Friday.
DAN (Caller): Yeah. Hello. How are you?
DAN: I'm a brewer (unintelligible) myself. I have been in the business for 12 years. I started in Germany and somebody just asked earlier about how the yeast strains are separated and breweries when they - when a primary fermentation is over, they just harvest the yeast, and on a lager style, the yeast settles on the bottom. The lower most layer is dead or not suitable for brewing. And they just scraped the top off and they'll reuse it. And with ales, our top fermenting and swim on the top. It much easier to harvest. You just kind of scrape it off the top, and there are quite a few breweries that are just reusing and reusing the same yeast from that batch.
So, some of these older breweries especially in Belgium and England and certain Germany, you have some very old yeast strains that have been used considerably. And I'm sure they're changing over time, but they're still being used though the flavors may have changed. The (unintelligible) may have change, but the yeast itself is essentially untouched.
PALCA: Well, thanks for that call. Unfortunately, that's going to have to be the final word because we've run out of time. Gavin Sherlock, thank you very much for joining me.
Dr. SHERLOCK: Thank you.
PALCA: Gavin Sherlock is an assistant professor in the Department of Genetics at Stanford University School of Medicine in Palo Alto in California.
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