Before Dragon*Con last week, Robin and I spent an evening with our old friends Bill and Jenn. What evening between friends would be complete without the consumption of adult beverages? In particular, Jenn’s deadly and delicious blueberry martinis?
Being the nerdy physicist that I’ve always been, I took my martini glass in hand and thought. Why are these particular glasses this odd shape?
The Wikipedia page on glassware gives a good overview of the different types of glasses. Until I started appreciating alcoholic beverages (over the age of 21, of course), I never realized exactly how many different types of glassware there are. It seems that just about every class of beverages has its own associated glass container. Even beer drinkers are particular about what they drink out of a pint glass, pilsner glass, bottle, or (sigh) can.
To put it terribly analytically, a glass is a potential well. When you pour a liquid into a glass and it comes to rest, the molecules don’t have enough total energy to make it out of the bowl of the glass. They stay there until they get enough energy to leave, or the walls around them disappear. This happens by one of three mechanisms.
First, you could make a pressure differential between the ambient air pressure and a region of the surface of the liquid. Because of the lower air pressure below your lips, atmospheric pressure pushing down on the rest of the liquid’s surface causes the liquid to ascend upwards in the region with lower pressure. Complex? Not really — you probably do this either by slurping or by using a straw.
Second, the random motion of a single molecule’s neighbors could happen to give the molecule enough energy to break through the intermolecular forces holding the molecule in the liquid. You can’t really plan this; it’s called “evaporation” and it just happens. Since you can’t actually productively imbibe any of the evaporated liquid anyway, this doesn’t really count.
Finally, and probably most frequently, you tip the glass (intentionally, sipping; unintentionally, spilling) to produce a spot in the near the liquid’s surface where the wall containing the liquid effectively disappears. Now that the liquid can be free, it is. Molecules nearest the gap in the wall fall out of the glass, hopefully into a waiting mouth below. Voilà, you’ve now tasted blueberry martini.
(Quantum wine in a potential well might leak out of the sides of the glass due to the process called quantum tunneling. Classical wine has no such problem. More on that some other time.)
So that’s why glassware works in the first place. But why do different glasses look so different when their purpose is the same?
Their purpose is not the same.
Some beverages are designed to stay at a constant temperature for as long as possible. Martinis and wines are a great example. Once the beverage leaves the temperature-controlled environment in which it’s stored or made (a cocktail shaker for the martini, a sommelier’s cellar or refrigerator for wine), normal heat transfer sets in. This means that the beverage will slowly start to creep towards the ambient temperature of the room. Or worse, the temperature of the hand holding the glass. The proper hand position to hold a wine glass is actually something like this:
CC-licensed photo from deepwarren on Flickr; original here
Holding a wine glass with the hand wrapped around the bowl will transmit a great deal of heat into the wine, changing its flavor (for the worse).
The purpose of a brandy snifter, on the other hand, is designed to transmit as much heat from the hand as possible to the liquor inside. Notice that the hand completely cups the bottom of the bowl, heating the brandy and allowing the vapors of the beverage to be released.
Credit: Wikimedia foundation
Certainly there’s a great deal of history that has gone into the shapes of glassware. The history of glassblowing itself is much to blame — it’s tough to make functional, resilient pieces of glass.
At least you don’t have to understand why glasses are designed the way they are to appreciate a tasty adult beverage. Drink up!