View Full Version : A Physics Problem, With Bourbon.

12-18-2011, 23:47
You have two barrels of bourbon, next to each other in a warehouse. One barrel holds 5 gallons, the other one 53. The warehouse is neither heated nor cooled. Temperatures inside, like those outside, can exceed 90 degrees in summer and drop below zero in winter. Ambient temperature can change 30 or more degrees within a 24 hour period.

Does the whiskey's response to these temperatures vary according to the size of the barrel. It seem that the whiskey in the five gallon barrel would follow the ambient temperature more quickly and closely than the whiskey in the large barrel, which would tend to change temperature more slowly. Am I right? How much difference would there be?

Also, the volume of a liquid expands when it gets warm and contracts when it gets cold. Would the liquid in the small barrel expand/contract more, as a percentage of its volume at the baseline temperature? Or would they expand/contract to the same extent?

This isn't a quiz. I'm asking because I don't know the answers.

12-19-2011, 01:47
I also believe it would have greater contact with wood in the smaller one (better liquid to wood ratio). I might be wrong.

12-19-2011, 05:01
the temp in the small barrel will change in temperature quicker than the temp in the big barrel. I know this, becuase I have watched it with a thermometer.

12-19-2011, 07:40
These two theoretical barrels are in a warehouse full of other barrels, right?

That warehouse full of barrels holds a lot of thermal mass, which regulates temperature swings of all the barrels. Yes, the barrels on the outside and near the roof will swing more quickly, but even that is tempered a bit by the overall volume of whiskey.

Tom Troland
12-19-2011, 07:45

I'm in a physics department, so let me give this one a try.

The amount of heat (thermal energy) in a barrel depends upon the volume of liquid. The change in heat depends upon the surface area since heat is gained or lost to the environment through the surface. So the rate at which heat is gained or lost depends upon the ratio of surface to volume. Surface is proportional to R^2, where R is some dimension of the barrel, say, its width. Volume is proportional to R^3. So surface-to-volume is proportional to 1/R. That is, if R is smaller (smaller barrel), then the surface-to-volume ratio is larger, and the barrel changes temperature more quickly in response to its environment.

If you compare a 5 gallon to a 50 gallon barrel, the volume ratio is 10, so the ratio in R is the cube root of 10, about 2. So the 5 gallon barrel should gain or lose heat (hence, change its temperature) about twice as fast as the 50 gallon barrel.

All of this sounds rather pedantic since it just reflects what you intuitively know (and what Tom McKenzie determined directly). Smaller things heat up or cool down faster. So if you cut a hot baked potato into small pieces, it cools off faster. And, by the same token, the smaller Moon has cooled off inside much more than the bigger Earth. So don't go the Moon expecting to see active volcanoes. Go to Hawaii, instead, where the climate is much more agreeable.

As for thermal expansion or contraction, the fractional (i.e. percentage) change in volume of a liquid with temperature does not depend upon the volume. At 20 C, for example, the coefficient of thermal expansion for water is 0.0002 per degree C. So if the temperature changes, say, 10 C (18 F), then the fractional change in volume is 0.002 or 0.2 %, independent of the total volume. This is not a very large change!

Of course, all this physics means very little compared to taste. At least in whiskey. And you recently reported on the failed Buffalo Trace experiment with small barrels. Turns out, they don't work very well. Evidently, small barrels are just a shortcut to get lots of color and wood flavor in a short period of time. But there is much more to aging whiskey than color and wood flavor.

So, did I pass the quiz?

12-19-2011, 07:50
The change in density as temperature changes is dependent on what the liquid substance is. Here is a chart for pure water:


There is a chart for ethanol on this page. Scroll to the table "Properties of aqueous ethanol solutions":



Bourbon Boiler
12-19-2011, 16:11
I don't disagree with any of the answers stated previously, but I think there's another variable that exagerates the results. Because of the higher surface area / volume ratio of the small barrel, there is more empty space (proportionately) within the smaller barrel. I've heard varying reports on how much the barrel absorbs in the first 24 hours, but we can assume it is noticable.

A small amount of liquid will change temperature faster than a large volume, but even at the same size a liquid that fills a container half way will fluctuate more than a liquid filling its container.

12-19-2011, 16:28
i think Tom has put out some good stuff, but there still is a rather perplexing variable still left out.

Them angels still take their fair share.

One would have to also figure in, at some fixed variable that may or may not hold true for every barrel in every warehouse everywhere, of the ever diminishing amount of whiskey in the barrel. As the volume goes done, i'm assuming that the ratio of liquid to wood contact will also change. Which then changes the above mentioned figures.

Sounds like a good topic to write some doctoral dissertation on.


12-19-2011, 17:49
Sounds like a good topic to write some doctoral dissertation on.

Anyone good at writing grant requests? I'm thinking a ten-year study, including well-constructed experiments involving close work with the bourbon manufacturers, a Scotch whiskey control group, with the future vision of creating a permanent Bourbon Aging & Tasting Institute. I wonder if UKY has any lab/office/lounge space to spare...


B.B. Babington
12-19-2011, 19:45
For raising or lowering barrel temperature, response to temperature varies dramatically by MASS of the liquid in the barrel. The smaller barrel will change temperatures much faster in relation to ambient temperatures.

Assume full barrel of 63% ethanol by weight (weight, not volume): to raise the temperature of the liquid by one degree celcius it requires 51.36 kilojoules for the 5 gal barrel and 544.45 kilojoules for the 53 gallon barrel.

Calculations were my own based on density of solution of 0.88 g/ml and heat capacity of solution of 3.0838 J/(g*C) for 63% ethanol/water by weight beginning at 20 degrees celcius; and assuming constant pressure (atmospheric pressure, volume can change).

For change in volume of liquid, it is as Tom said. Easier to calculate based on ethanol since thermal expansion coefficient for ethanol is much greater than water. There are experimental papers with specific data for different ethanol/water mixtures if that is needed.

12-19-2011, 22:07
Wow, this is getting deep! Kilojoules, R^2, R^3, Coefficient of thermal properties...But, ya'll are missing the simple answer....Put a barrel of new make in a DeLorean, hit the flux capacitor with 1.21 gigawatts of electricity, obtain a speed of 88 MPH, and you're back in 1955 with a barrel of VVOF....Easy....;)

12-19-2011, 22:45
Wow, this is getting deep! Kilojoules, R^2, R^3, Coefficient of thermal properties...But, ya'll are missing the simple answer....Put a barrel of new make in a DeLorean, hit the flux capacitor with 1.21 gigawatts of electricity, obtain a speed of 88 MPH, and you're back in 1955 with a barrel of VVOF....Easy....;)

:eek: 1.21 jiggawatts!!!

12-20-2011, 04:14
Wow, I ain't that smart. i have a headache now.

12-20-2011, 04:53
"holds 5 gallons" is somewhat ambiguous. Is the barrel with 5 gallons a smaller barrel, or is it a large barrel with only 5 gallons in it?

12-20-2011, 06:22
"holds 5 gallons" is somewhat ambiguous. Is the barrel with 5 gallons a smaller barrel, or is it a large barrel with only 5 gallons in it?

He is talking about a smaller barrel.


12-20-2011, 07:51
All very helpful and, as I said, I asked the question without knowing the answer. In discussions about the effects of small barrel aging, we talk a lot about the increased surface contact but it occurred to me that the response to ambient temperature might be just as important, although Barturtle makes the good point that, in the Buffalo Trace case, the 5 gallon barrels were probably in the warehouse with a lot of 53s and the mass of the liquid in the warehouse creates a different condition than if the two barrels were not surrounded by others.

One surprise about the tasting was how much raw wood flavor there was in the small barrel whiskeys and thinking about that, and the increased evaporation, made me think about how the little barrels would be more influenced by outside temperature changes.

12-20-2011, 09:33
Some other details to consider is the red layer in the wood and barrel proof of the liquid. Smaller barrel staves will have less caramelized sugars in the barrel stave. It may take a lower barrel proof to get the sugars out of the wood since sugar dissolves bet in water than alcohol. Small barrels are great for adding wood tannins, but it takes more than tannins to make a good bourbon.

Mike Veach

12-20-2011, 10:28
Smaller barrel staves will have less red layer sugar but also there is less whiskey for it to impact (as compared to a standard barrel)...

The more rapid cooling and heating described by Tom is interesting, but if the cycles produced by nature aren't increased (which could only result from mechanical heating I would think), that should not of itself improve maturation. You can hold in your hand a normal-size hot potato sooner than a softball-sized one, but they should taste the same.

The one thing I can see that should make a difference by using small casks vs. larger, and all other things being equal, is the greater surface-to-liquid ratio. That will bring barrel flavoring elements into the whiskey faster. That is why Chuck tastes a good wood effect in most of the whiskeys aged in these containers and released at 1-2 years, IMO. What that won't do is oxidize the whiskey significantly faster because oxidation takes time. You can test this by pouring an ounce of any whiskey into a 26 oz bottle. In time it will oxidize, not right away, and it varies for the type of whiskey and age, but it will acquire a dirty metallic taste in time. It may be months, it may be some years, but it will happen.

With barreled whisky of any container size, I believe you need about 4 years to get a product which has the taste most would associate with a well-matured whiskey. It's not to say younger whiskeys aren't good and don't please many palates.


B.B. Babington
12-20-2011, 17:50
...With barreled whisky of any container size, I believe you need about 4 years to get a product which has the taste most would associate with a well-matured whiskey....
That's my thought, too. Perhaps with more inventive char techniques they can mimic the maturation. Maturation is more than wood alone. I've tasted many variations on the theme of increasing surface area and these techniques do increase wood flavor but don't bring product up to the standard one finds in the well aged material.

I do vary much enjoy the wood experiments like Woodford Seasoned Oak and Maple and always on the hunt for the next wood experiment.

Bourbon Boiler
12-20-2011, 20:57
I wondered why I always felt smarter after a few drinks, now I know it was training for this thread.

12-22-2011, 18:16
Surface area is important, but so is the depth and volume of absorption by the wood.
If the SA/Vol ratio is greater and the volume of whiskey in the wood increases, then the wood effect would be amplified disproportionately.
I would even venture that thinner staves might synergistically absorb whiskey as the transpiration (Angel's share) would be increased in smaller barrels.
The thickness of the red layer contributes sweetness.
I would propose that with increased SA/Vol, the exposure to red layer is increased as well, but penetration through the red line might be increase, increasing tannin.
The more rapid cycling that has been proposed would result in significant increase in transfer across the charred layer.
My conclusion is that small barrels would give greater wood effect, but the conversion of molecules to smaller ketones and esthers would be less.
Overall this would be more creosote/tar-like qualities and less sweet and floral notes.

12-22-2011, 21:55
So, would thicker staves or a finish as done with Maker's 46 improve the flavor from small barrels?

12-23-2011, 05:03
It has been my experience that thinner stave work better on small barrels. I think it allows for more oxidation. the biggest thing you do not get with small barrels. A lot of the trouble with the micros that are using small barrels is, and I have said before is, the white dog they use has little taste and they go in at too high a proof.

12-23-2011, 16:38
You really can't fix bad whiskey, unless you redistill it into vodka. A whiskey aged in a 5 or 10 gallon barrel probably gets as good as it is going to get in about two years. A 15 might go a little longer and I'm not sure it's even fair to call a 30 gallon barrel small, but the jury is still out on that one. Anyway, I'm not saying they're good at 2 years, they're just as good as they're going to get.