At The Surface - In Which I Try to Articulate Why This One Obscure Science Idea Isn’t Totally Boring

I don’t go in for a lot of cocktail science, and I don’t often read about it. Cocktails are more in the arts and crafts world to me, about composition and feeling more than molecular interaction.

This isn’t new for me. The toughest science class I’ve taken is biology for non-science majors, a borderline gut course since I had already taken Bio 1 and 2 in high school. As for math, my Algebra 2/Trig class in high school was probably more rigorous than the statistics class I took to meet the bare minimum required for a Liberal Arts degree. I wasn’t bad at math or science, just disinterested. Then and now, though, I like reading about science as long as it’s an article not much longer than a few pages. Might even read a book on the subject if it’s fictional.

There is one scientific concept that I find fascinating: the Surface Area to Volume Ratio (SA:V). It’s a simple idea - how much of something is close to it’s surface? - yet it explains so much about the way the universe works. I feel compelled to share my enthusiasm; SA:V is an often-ignored key to understanding how both cocktails and everything ever operates.

Let’s start with a brief rundown. Here are some examples of SA:V and its effect across different fields of study, to give you an idea of how often it comes up:

 

  • Zoology: Jackrabbits have big ears because they live in the desert. When they get hot, they stick their ears out, increasing the amount of their blood that’s close to the surface of their bodies, which lets it cool off. When it’s cold, they can pull their ears tight to their bodies, reducing their surface area to conserve heat.
  • Geography: Peninsulas and areas around bays and inlets are, on average, more affluent than areas that are landlocked or that have smooth coasts. Markets for goods and services naturally arise near the shore, because goods travel easily at sea, and specifically near safe harbors, which facilitate the smooth transfer of goods between land and sea.
  • Your Butt: the volume of the human colon is only about 4 pints, but it’s super wrinkly. If you stretched it out, it could cover a tennis court - that SA:V is off the chain! The colon is designed to re-absorb water used previously in digestion through its lining before that water can leave the body, and to do it in a relatively compact space.

 

The list is endless, so I’ll cut it here. Before we move on to how relative surface area informs the art and science of serving drinks, let’s take some time to look at two universalities among all of these examples. First, size and shape affect the SA:V of an object. For size: the bigger something gets, the lower its SA:V - that is to say, the farther parts of it get from its own edge. Picture a cube that’s 2 inches across. That cube has a volume of 8 cubic inches (2” x 2” x 2”) and a surface area of 24 square inches (2” x 2” x 6 sides). The SA:V of the 2 inch cube is 3:1.

Now imagine you cut that cube in half, then quarters, then eighths so that you have eight cubes that are all 1 inch across. The volume is unchanged at 8 cubic inches (1” x 1” x 1” x 8 cubes), but the surface area has increased to 48 square inches (each cube has 6 sides that are each 1 square inch, and there are 8 cubes). The SA:V of those cubes (and of each individual cube) is now 6:1. Why? Because the pieces are smaller.

For shape, the more compact something is, the lower it’s SA:V. Take those eight 1 inch cubes and imagine fusing them into a single stack that is 8 inches tall. We still have same volume, 8 cubic inches (1” x 1” x 8”), but the surface area is now 34 square inches (2 x 1” x 1” squares plus 4 x 1” x 8” rectangles). The SA:V of the stack is now 4.25:1, still up from the original 3:1. Why? Because the shape is less compact. (The most compact shape, and therefore the one with the lowest SA:V, is the sphere. More on that in a sec.)

The second universality among these examples is that an object’s surface tends to be where the magic happens, and by magic, I mean all manner of transfers. Heat transfer (jackrabbit ears), cellular osmosis (up your butt), the transfer of money as goods go to sea - all of this happens at the edge, or surface, of a thing. More surface area means more transfers, and those transfers are magic. (That’s probably why humans are more magical than giants, but less magical than elves. It’s just science.)

Okay, now that we have that foundation, let’s get to what all of this has to do with booze. Here are a handful of ways that SA:V effects what we drink and how we drink it.

 

The Distillation Process

Distillation is one of the cornerstones of the adult beverage industry. Mash something with sugar in it, like fruit or grain, and let the juices sit to ferment. You get beer or wine, and it’s a naturally occurring process. Put that fermented juice into a pot still, though, and it is heated until it turns into a gas. Once it evaporates, it moves into long, thin tubes (with a high SA:V) that transfer the heat away in a controlled manner so that the alcohol vapor turns back into a liquid, while the water vapor largely escapes.

The results are basically magic. You have the distilled essence of what was once a living thing. You have its spirit, the water of its life. (Whiskey, vodka, and eau de vie all pretty much mean the same thing: water of life.) And this happens, at least in part, thanks to a rapid change in SA:V as gas passes through different shaped containers.

 

Ice Size, Shape, and Clarity

Key to any discussion of ice and the way it interacts with a drink is understanding that ice only melts at its surface.

Size: The larger an object of any shape, the lower its relative surface area. Fancy cocktail bars often use silicone ice cube trays to make the largest possible ice cubes that will fit in their glasses only in part because they look cool. Since the relative surface area of the ice is lower, and since it only melts at its surface, the larger-format ice will melt more slowly than a similar volume of ice in smaller cubes. At my bar, we use these heart-shaped silicone trays for our large-format ice, because they’re big and also we love you.

Shape: The shape with the lowest SA:V is the sphere, and the bigger the sphere, the lower its SA:V. That’s why big ice balls are a thing. Similarly, cubes have a lower SA:V than rectangular prism shapes, which is one of the reasons people started geeking out a few years back about ice machines that create perfect cubes. Because of their low SA:V, big spherical or cubic ice melts relatively slowly and is ideal for serving strong drinks intended for slow sipping - straight spirits and boozy cocktails like an Old Fashioned. For tall, refreshing drinks, like a Collins, smaller and therefore faster-melting ice may be the better option.

Because we want the ice to melt, while big spheres or cubes are ideal for serving many drinks, I’ll use smaller ice to prepare any drink. Ice cools and dilutes cocktails by melting, and that happens faster with smaller pieces because they have a higher SA:V. It’s also faster, cheaper, and easier to make smaller pieces of ice, so economic factors push towards making small ice the default for prep. You may even see bartenders at high end bars hand-crack large cubes into smaller pieces before stirring a drink, which seems wasteful.

Clarity: Most water has particles suspended in it - minerals, gas, sanitizing chemicals, that sort of thing. When water freezes, it traps these particles, which create tiny pockets inside the ice that make it look cloudy and greatly increase its surface area, which in turn makes the ice melt much faster. You can avoid this problem when freezing your own ice by insulating the bottom and sides. The only exposed surface will be the top, and instead of freezing from the outside in it will freeze from the top down, forcing suspended particles to the bottom.

To do this at your home or bar, fill a cooler with water, leave the top off, and put it in a freezer. The next day, you should have a cooler-shaped block that’s almost completely clear. We do something similar with our heart-shaped trays by doubling them up. By putting one inside another, the bottom and sides are insulated. Even at the 1” depth of our silicone trays, the difference in clarity is noticeable.

 

Glassware Shape and Temperature

Shape: What’s the difference between serving sparkling wine in a flute versus serving it in a coupe? SA:V. A tall, thin flute only has a small circle of surface area, which is where gas escapes, while a coupe has a relatively large surface. Flutes, as a result, keep Champagne bubbly longer than coupes do. It’s faster to pour into a coupe, though. Since the escaping gas can dissipate more rapidly, a quickly poured glass is less likely to foam over in a coupe than in a flute. So if long-lasting carbonation is the goal, a flute is the best option. If speed of service is more important, go with a coupe.

Another advantage for the coupe is aromatic. If that surface is bigger, the aroma of that drink will be more intense. Drinks that smell real nice do well in coupes, Martini glasses, or wine glasses for that reason. Drinks that smell kinda weird (like egg white drinks) I’ll instead serve in a single Old Fashioned glass or another vessel with a similarly small surface area.

You can also alter the surface area of the contents of a glass by tilting it. Hold a flute straight up and down, and the surface of anything in it will be a compact circle. Tilt it, and the surface of its contents begins to stretch. That’s why you should tilt it when you pour beer into a pilsner glass or Champagne into a flute. The liquid will also spread out as it runs down the inside of the glass, which further increases its surface area. All of this will help prevent unwanted foaming.

Temperature: High quality glass is very smooth at a microscopic level, and carbon dioxide needs to find a little foothold in the glass to attach itself and form bubbles. Think of it like climbing a cliff: if that cliff is perfectly smooth, you can’t grab on and you’ll never make it to the top. The SA:V is too low. If that cliff is more jagged, with outcroppings to grab, it’s much easier to climb. The increased SA:V makes it easier to hold on. The same basic idea holds for tiny bubbles on the inside of a glass.

Changing the temperature can also change how smooth its interior is. If a glass is refrigerated, it’ll develop condensation on its surface, and that water will smooth over some of its natural imperfections and reduce foaming. That’s also one of the reasons some beer bars rinse all of their glasses before pouring drafts. Frozen glasses, however, are covered in tiny ice crystals, which create a very jagged surface. As a result they actually increase the rate of foaming.

Despite this inconvenience, we use frozen glassware for draft beer at my bar. Why? Because it looks cool, and the “ooh aah” factor of a frozen schooner makes people okay with getting a 12oz beer instead of the now-standard 16oz pint. In order to keep the beer from foaming over, we employ a technique called the “Husam Swirl”, named for it’s creator, Husam “Sam” Halhuli, who was a bartender at my spot for a couple of years before recently moving home to open his own cocktail dive in Tacoma, WA.

To execute a Husam Swirl, pour a half-ounce or so into the frozen glass and then stop. The first run will always be a little foamy, especially if you haven’t poured from that tap in the last few minutes. (Many bartenders will just let the tap run for a sec, but then you’re wasting good beer.) Swirl the glass around to coat the sides in beer, which will melt the ice on the inside of the glass creating a smooth surface. It will simultaneously expel much of the gas from that heady beer you already poured. Then you can pour into the glass normally, and the glass will behave more like a chilled or rinsed glass than a frozen one. Ta da!

This is about the point when I would get bored reading an article about cocktail science, so I’ll cut myself off. Rest assured, this is just the proverbial tip. Pretty much everything I can think of somehow comes back to the SA:V. (Microfiber! Bronchioles! Okay, I’ll stop, I’ll stop.) On top of that, there are probably a million other scientific concepts that could similarly inform my universe, but I never heard of them because I was a lazy student. Every day I regret not taking more hard math and science classes when I had the opportunity. Kids, take note: work hard in school. Some day you may grow up to be a bartender!

 

1 Comment
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Hand cracked ice in the stir

August 19, 2016 01:17 PM by Frederic Yarm

There are two reasons why hand cracking ice can work well. One, bigger cubes have a hard time sitting well in a mixing glass and stack (such that most of the ice is above the surface of the drink). Two, it accelerates the dilution and chilling and if it is done with the same number of cracked cubes, it can be consistent for time/revolution.

The main reason that I do not crack ice is that I'd rather the guest not see me bear-pawing ice cubes that go into their drink. I don't mind a bartender's hands touching a garnish like a citrus twist inserted into my drink, but having ice handled like that does not instill ideas of cleanliness but faith that alcohol will sterilize everything. (And for some reason, I was okay with Gary Regan's finger stir at Cocktails in the Country last year.)

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