🥃Whiskey Stones - Do they Work? Science Answers

 Every now and then, I get acquisition fever and go scroll amazon looking at whiskey glasses, bar accessories, and grilling paraphernalia, none of which I need. I'm always intrigued by the concept of whiskey stones. It sounds like a great idea: put these little fellas in your cup to cool it without watering down the good juice. But do whiskey stones work? I decided to pull out the spreadsheet and some high school physics to find out. 

The Contestants

A la Jeff Bezos, I grabbed four of the more popular material options from Amazon. In general, individual stones seem to be around 28grams though the bullets are a bit larger and the relative weight of the filled stainless steel cubes a bit lighter.

Overly Simplified Science 

Heat is a form of energy that can transfer from one object to another due to a temperature difference (yes even cold things have heat energy). Specific heat is a material property that tells you how much heat energy is required to raise the temperature of a unit mass of that material by one degree (Celsius or Kelvin, they're the same increment just a different zero). Like all good non-lumber based calculations this exercise will be done in metric units. 

The basic equation for heat transfer entails finding the total heat capacity of a material by multiplying the amount of that material (mass) by the temperature in Kelvin  and the specific heat to get amount of heat energy in the material at a given starting temperature. 

Disclaimer: For this exercise we're going to use some simplifying assumptions, but don't worry the results are very conclusive.

Basic Heat Transfer Equation

Q = mcΔT

Here's what each symbol represents:

• Q: The amount of heat transferred (in Joules)
• m: The mass of the material (in kilograms or grams just make sure your c value has the same units)
• c: The specific heat of the material (J/kg⋅K ) 
• ΔT: The change in temperature (final temperature - initial temperature)

As mentioned, multiplying by temperature instead of change in temperature gives you the total energy of the material in Joules.

Whiskey in a Glass - Stones Built to Last

To find how much the temperature of whiskey will change with the addition of the whiskey stones, we simply take an average of the heat energy in the whiskey and the heat energy in the whiskey stones weighted by their mass times specific heat. 

Resulting Temperature  =(Qwhiskey+Qstones)/(MassWhiskey*SpecificHeatWhiskey+MassStones*SpecificHeatStones)

Along the way, we'll make those simplifying assumptions:

• Heat transfers perfectly between the liquid and stones
• No heat is lost to the glass or air - the size and shape of a glass can very significantly and that is unnecessary noise (Idealized System) 
• Specific heats are constant over the temperatures involved
• For blending specific heats we'll use a basic weighted average by mass

It's a simple Matter of Weight Ratios

Temperature wise, we need to pick a starting and ending point. My bottles of bourbon are all in a lovely little dark cabinet above my desk. It keeps the light from damaging the brown and also means that I can happily top off my pour while gaming (maybe a little too convenient if I'm being honest). The byproduct of this is that the liquid is sitting at your standard room temperature.

Starting Temperature of the Whiskey: 72 Fahrenheit which is about 295 Kelvin or 22 Celsius

Volume of the Whiskey: 

A standard double pour of bourbon is 88ml, whiskey is 94% as dense as water, so we have a starting bourbon mass of 83grams. Let's pretend that that's our normal serving size (for science you know). 

Heat Energy of the Whiskey: 

Taking our lovely 83grams of whiskey at 94 proof we end up with a specific heat of 3.38j/g, about half way between the values for water and ethanol. One more multiplication step to take the mass, specific heat, and temperature together, and we get 82.6KJ (82,636J).

Peep the chart below:

Right off the bat, we see that Water has a relatively high specific, requiring almost ten times more energy to change one degree than steel. Metals have very low specific heat and conduct heat energy well while organic molecules like alcohols take more energy to change temperature. Without doing any math, this chart alone tells us that the soapstone, granite, and steel whiskey stones will require a lot of mass in order to have an impact on our Whiskey's temperature.  

Heat Energy of the Stones:

Following the USDA guidelines, our freezer is set to about 0 degrees Fahrenheit or 255.35Kelvin. This gives us a starting temperature difference between the whiskey and the whiskey stones of 39.8K. Quickly multiplying the mass of the whiskey stones, their specific heat, and the starting temperature gives us the following energies per whiskey stone and for all stones total in the package. 

Taking the Weighted Average:

Our last step is to take the energy in the whiskey and the energy in the whiskey stones, add them together, and then divide by the total mass times specific heat of the two materials to get the temperature of the combined system.

Assessing the Result 

Despite having less mass, the higher heat capacity of the Stainless Steel cubes filled with a combination of Glycerol and Water made them far and away the winner of this test. A single cube can lower the temperature of the whiskey by 7.2 degrees versus half of that number for the next nearest material, soapstone. Conventional wisdom suggests that whiskey is best consumed at slightly below room temperature, somewhere between 60 and 65 degrees imperial or 15-18 Celsius. If our shelf is at 72F/22C, then we only need one stone to get to the top of the recommended range. I would probably use two just to be safe (hit the lower end of the range and have some wiggle for time to consume/heat lost to the glass). To accomplish the same thing with the other options, you'd have to dump in about half of the pack which starts to look a bit silly. Somewhat underwhelming to me is the fact that even if you dumped all of the stones into a comically wide glass, you still would only be able to get a hair under 50F. Similarly, you could cool two glasses for yourself in one evening at our very tiny 88ml pour though after that it takes about 3 hours to get the stones back down to temperature. 

Evaluating the Alternatives - Ice Ice Baby

At this point, you might be asking: should I just use ice instead? If we look back at our specific heat chart, you may note that ice has about double the heat capacity of soapstone, but then something magical happens: it melts. Water, because of the hydrogen bonds that give it many unique characteristics, requires double the energy to heat in its liquid form versus when it is frozen. This means that as the ice melts it actually sucks up more of the heat energy in the glass, further pulling the resulting final temperature down.

It's Something Chemical - Guaiacol at Work 

We should also note that the addition of small amounts of water is actually enhancing to the whiskey's flavor instead of being detrimentally dilutive. You may have seen a whiskey "Pro" put a tiny drop or spritz in their Glencairn right before nosing. Guaiacol is an aromatic compound found in whiskey, particularly those matured in charred oak barrels, and contributes to the smoky and woody flavor profile we know and love. It is partially soluble in alcohol and water but slightly more so in the booze. When we add nonhomogeneous water such as by a spritz or ice melt, it creates a gradient by which Guaiacols move closer to the alcohol molecules in the glass, increasing the relative concentration of these woody elements. Your olfactory and taste receptors pick up on these pockets of flavor leading to increased perception of smell and taste. Careful Icarus! Flying too close to the sun will melt more ice than needed and you'll undo this delicate balance.

Ballin'

If you are going the ice route, you should know that ice balls don't just look fantastic, they're also more effective than their cubical counterparts. Spheres have around a quarter less surface area than cubes of the same width, resulting in slower ice melt and dilution over time. Watch your pace though because they're usually quite large! That chonker of a globe is likely good for three drams at optimal dilution, proceed with caution. Speed of melt will accelerate over time, so optimized use will leave you with a still somewhat intact ice ball. Consider pairing your majestic frosty boy with a double walled or otherwise insulated glass. 

Are Whiskey Stones Worth it?

No, but...

Like most real world decisions, the optimal path largely depends on what you're trying to achieve. 

• Looking Cool - The bullets or actual stone based whiskey stones were quite poor at actually cooling a beverage and are best avoided unless you just want the aesthetic look of having them in your glass. 
• Optimizing Flavor - 80 to 100 Proof - At this proof, you don't want much if any dilution in a "Good" whiskey. This is the ideal space for one of the higher heat capacity whiskey stones such as the stainless steel cubes filled with water/glycerol. You'll get the drop in temperature without severely impairing the flavor experience with excess melt. Consider a small ice chip or drop of water to open up complex pours if needed. Alternatively, you could just pop your glass in the fridge for a few minutes before drinking. 
• Optimizing Flavor - Bonded to Hazmat - High proof whiskeys almost always benefit from a little dilution. Experience suggests around 5ml or 1/20th the volume of whiskey in ice melt or water spritz can "open" up a high proof spirit. This is prime ice ball territory. If you're microdosing these big boys, maybe a whiskey stone or two could play a role but I doubt the minor drop in temperature will temper the alcohol much if any. 
• This whiskey is $H1T3: The highest and best reason to chill a whiskey is because you're not actually interested in tasting the whiskey. Maybe it's bad. Maybe it's time to party. Whiskey stones aren't going to do you a lick of good here. Take that bottle out of the freezer and put in regular ice cubes. Get that melt going and sip off to the races (responsibly)!