Sound Speed in Bourbon

Does sound travel differently in Kentucky bourbon than it does in other types of alcohol? Stanley A. Cheyne of Hamden-Sydney College pondered this question before the 177th ASA meeting in Louisville, Kentucky. Twenty or so types of whiskey later, he’d made some interesting discoveries, both about whiskey and about how distilleries measure alcohol concentration. This episode we interview him about his resulting article in Proceedings of Meetings on Acoustics, “Sound speed measurements in ethanol/water solutions and Kentucky bourbon whiskey.” 

Associated paper: Cheyne, Stanley A. “Sound speed measurements in ethanol/water solutions and Kentucky bourbon whiskey,” Proc. Mtgs. Acoust. 36, 045008 (2019); https://doi.org/10.1121/2.0001396.

 Read more from Proceedings of Meetings on Acoustics (POMA).

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Music Credit: Min 2019 by minwbu from Pixabay. https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=music&utm_content=1022

Transcript

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Kat Setzer (KS)

00:06

Welcome to Across Acoustics, the official podcast of the Acoustical Society of America’s Publications office. On this podcast, we will highlight research from our four publications, The Journal of the Acoustical Society of America, also known as JASA, JASA Express Letters, Proceedings of Meetings on Acoustics, also known as POMA, and Acoustics Today. I'm your host, Kat Setzer, Editorial Associate for the ASA.

Joining me today is Stanley Cheyne of Hampden-Sydney College. We'll be discussing his article, “Sound speed measurements in ethanol/water solutions and Kentucky bourbon whiskey,” which appeared in Proceedings of Meetings on Acoustics and is based off a talk he gave at the ASA’s 177th meeting in Louisville, Kentucky. Thanks for taking the time to speak with me today, Stan, how are you?

Stanley Cheyne (SC)

00:57

I'm doing just fine. Thank you.

KS

01:00

Awesome. So first, tell us a bit about yourself and your research background.

SC

01:04

Okay, well, I earned a bachelor's degree in physics from Hendrix College, which is in Conway, Arkansas. And then I got a master's and a PhD in physics from the University of Mississippi, and I'm in my, currently in my 33rd year in the Department of Physics and Astronomy at Hampden-Sydney College. Hampden-Sydney is a small liberal arts college founded in 1775, making it the tenth oldest institution of higher learning in the US. Since I've been here, I've been studying the acoustic property of bubbly liquids for the past 30 years. The presence of bubbles in liquids have a profound effect on the speed of and absorption of sound. For example, the presence of only 1% air in the form of bubbles in water can drop the sound speed from 1,480 meters per second to about 110 meters per second at certain frequencies. 

KS

01:59

Oh, wow. What led you to researching how sound travels in whiskey?

SC

02:04

Well, that's a very interesting question. Well at Hamden-Sydney, we're a liberal arts school. So we are. I've done a lot of different things here. And when I saw the meeting, the national meeting in Louisville, Kentucky, I thought, “Okay, we've got horses, we've got baseball bats, and we have bourbon whiskey.” And I found doing acoustics of bourbon would be a lot easier than trying to study the acoustics of baseball bats or horses. So I just thought it was a nice thing to look into.

KS

02:39

Yeah, totally. Sounds like a lot of fun. Great idea. And then you get to test whiskey, right? 

SC

2:44

I do, yeah. So how fun can that be?

KS

2:47

Yeah. So tell us about your experimental setup.

SC

02:52

Okay, the setup. First of all, I wanted to decide you have bourbon, what kind of acoustic properties do you want to measure? And to me, the most logical one was either absorption or sound speed, and sound… So I decided to go ahead and set up a, an experiment to measure sound speed. There's a variety of ways to measure sound speeds. But what I chose is what's referred to as the “time-of-flight method.” The time-of-flight method basically is relatively simple. You have one hydrophone, which is a microphone underwater, that is a source of sound, and then you have a second hydrophone as a detector of sound. And you send a pulse through one, knowing the distance between it, you measure the time of the flight of the wave, of the pulse, and just take distance divided by time, and you can come up with the sound speed.

KS

03:41

So did you  figure out if sound travels differently through whiskey than through ethanol and water? And in that same vein, did you see any differences among the various whiskies you tested?

SC

03:51

I started thinking, okay, I’ll start looking into bourbon what bourbon really was, and it turns out bourbon is really nothing more than ethanol and water solutions. The brown color, it actually just comes from the aging process in the barrel, and the ethanol-water interaction with the charred barrel. 

So what I thought first is first measure some sound speeds in ethanol/water mixtures. And so I just decided, how hard could it be, right? You just set up some—get ethanol mixed with water, and measure the sound speed. So I was all prepared to do this, and my naive self—and all the chemist’s already know this—that when you add ethanol to water, it's… all of a sudden, the temperature heats up, it creates bubbles, and the sound speed goes, you know, increases, by, you know, 10,15, 20 meters per second. And it took me a little while to figure out what was going on. So it actually, that actually threw a curve in all this. I thought it was going to be a lot easier than that. So if you find yourself trying to let the temperature cool down, it takes a while. So it was very time consuming at first, until I figured out really how to do the, take care of the temperature increase, and so forth. 

But so, another thing I learned about from my chemist friends, if you take 100 milliliters of water, and you mix it with 100 milliliters of ethanol, it does not add up to 200 milliliters; it adds up to about 196 milliliters. So actually the volume decreases, which means the density will increase. So that's another aspect of ethanol and water that I learned about and had to contend with. 

And, and so the way I solved all this is because if you take a mixture, it's at room temperature, then you add, you add about five degrees Celsius, it's going to take a long time to come down to room temperature. So I wanted to make measurements at room temperature first. So basically, what I did is I would get, mix ethanol and water, and I’d know the concentration. I would let it heat up. I would then put it in an ice bath to cool it down to about 20 meters per second. And then I would actually put it on a heater and had a magnetic stirrer. And I would measure the sound speed and the temperature at the same time. And so as the temperature would go up. And after I did this with about 20 different concentrations, I could then pick out the temperatures, the isotherms, I wanted to use. It turns out that there are many published results on ethanol/water sound-speed measurements, and they're all 23 degrees. And I'm pretty sure I know why they're at 23 degrees; it’s because anytime you add ethanol to water, the temperature increases. So everybody made these measurements at 23 degrees. And my numbers came out very favorably toward those. So my ethanol/water measurements, I thought were very good.

KS

07:11

Awesome. Did you find out if sound travels differently through whiskey, then?

SC

07:24

Well, this is what I found as far as—now, let's get to bourbon. 

KS

07:27

Yeah.

SC

07:28

Now there's an interesting issue I'll try to describe. First, I want to describe what the sound speed in ethanol/water kind of looks like in a graph. So I'm going to try to explain a graph. 

KS

07:41

Okay

SC

07:42

If you think of 0 ethanol, that means your sound speed and water at about 23 Celsius is about 1400—1482 meters per second. Up to about 30% ethanol, as you add ethanol up to about 30%, it increases to over 1600 meters per second. After that, it starts decreasing at almost a linear rate down to 100%, up to 100%. So it turns out that the nice thing about this, at 40% alcohol, you almost have a straight line, you almost have a linear relationship between percentage of alcohol to the water, which is really good. And the reason that's good is because all distilled spirits start at 40% or 80 proof or 40%. So any, my motivation here was trying to understand distilled spirits. And it's really nice. The fact, the area that I want to look at is linear. So any scientist knows that anything that's linear is always much easier to work with.

KS

08:49

So then I guess tying into that, with the various whiskies that you tested. Does that mean the sound speed just varies based on the proof for the whiskies?

SC

09:04

That's precisely what I found.

KS

09:05

Okay.

SC

09:06

Part of my experiment was to, first of all, I got some bourbons. I had a friend that provided me with about 15 to 20 different ones, and I had to go buy a few. And that was interesting to have all the bourbon in the lab, but I worked that out.  I wanted to measure the concentration of, how much ethanol? And it turns out the first thing I did, I used a floating hydrometer. And these are designed to measure the density of fluid. I found those to be time consuming. And also, I could only get percentages to 1% accuracy. So I wanted something different. So for this experiment, I just assumed what the manufacturer put on their, the label—if they said 40%, or 42%, or there are, some say 94.1%. I'm assuming that concentration was correct. So I was, so I put the bourbon, do the sound-speed measurements at room temperature—this was all done at room temperature—and I compared those measurements to my ethanol/water mixtures at room temperature (room temperature being 23 degrees Celsius). And they came out right on top of my ethanol/water mixture. So the brown coloring, it all, what I found, all that mattered was the temperature and the sound speed. And from those two parameters, you could determine what the percentage of alcohol was in the, in the distilled spirit.

KS

10:36

Okay, so we already kind of discussed the factors that seem to affect the speed of sound that travels through alcoholic solutions, it's temperature and alcohol content.

SC

10:47

Now, one thing I did notice, in the, in the data, there were, you know, several bourbons that were 40%. And there were several bourbons, there was, I don't remember which one was which, it seemed like it was like 91.3, a fractional percent. And there were some that were only off by less than 1%. And my sound-speed measurements actually resolve that. So I could actually see if it was, it was where it was supposed to be on the graph with it, even the small changes in concentration showed up, I could differentiate that in my in my data.

KS

11:25

That's super cool. Okay, so what is the impact of this research, then?

SC

11:31

The impact? That's a great question. I started to do more experiments. And I wanted to find a way to precisely measure the concentration of alcohol, ethanol/water mixtures. And it turns out, there is a device out there, and it cost me $4,000. And I bought one… The college bought one. And the mechanism—it was very precise. It basically, the way it worked, it would suck up some of the fluid, it was shaken in an oscillator, and knowing the temperature, it could determine the density of the fluid. And then it then converted that density to percent alcohol. So it, that's the way it worked. And it took, it would take about 30 seconds; most of that 30 seconds was not in the oscillation, but measuring the temperature of the fluid. And like I said, in this, this, this device was about $4,000. And I liked the device; it worked fine. Once again, it was it was expensive, though. 

And one of my motivations—I did not set out to do this, but after I saw the data, and saw that it wasn't very expensive to measure the concentration of alcohol in distilled spirits. My goal then was to design and build a device that could do this with a lot less cost. And, I've actually my prototype, I've done this with the help of one of my friends who's a computer programmer. And it I've done this for less than $100. 

KS

13:11

It's as Bob Ross would say, a happy accident.

SC

13:14

There you go. Like I said, I did not start off thinking I was going to build this device my first motivation was, the Acoustical Society meeting was in Louisville, Kentucky, and I think somebody needs to do something with bourbon.

KS

13:28

Yeah, right. Exactly. Yeah. I mean, that's reason enough, right? So do you have any future research planned in the same area, perhaps looking at propagation of sound through mint juleps? Or since you're a bubbles guy, what would this look like with beer or wine?

SC

13:45

Well, that's a great question. First of all, I've been making sound-speed measurements in bubbly liquids for a long time. And every time I mentioned that to one of my friends, they always say, “I have champagne and beer, Are you going to—that's a bubbly liquid.” And so it turns out, this method probably wouldn't work very well in beer or champagne, just because the bubbles would be dominant. not only do they change the sound speed, but they introduce a lot of sound absorption, so it would be more difficult unless you did flat beer or flat champagne. And you said mint juleps. Okay. Although I have not made these measurements, distilled spirits, most distilled spirits don't have many additives. And so when you start looking at wine there, I think the sugar content there, mint juleps and things like that, I think that sugar probably is going to have an effect. Anything you add to liquid is probably going to affect the sound speed. So if you want to keep it relatively simple, you know, ethanol/water, bourbon and Scotch would be good things to do, vodka would probably be good to do. And I might do—I actually plan to make measurements in those just to see. And, that's the question why not? So.

KS

15:02

Right, exactly. Well, thank you for taking the time to speak with me today. It's so funny to hear that this research you did on kind of a bit of a whim just ended up with a new invention, essentially. Maybe this will inspire some of our listeners to study how sound travels through barbecue sauce for the Nashville meeting.

SC

15:21

That's right, Nashville’s coming up. So yeah, I’m not sure. Barbecue sauce or, or country music. I'm not sure.

KS

15:32

Oh, yeah, country music, would be good.

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