Have you ever thought about your last drink?

It’s not as singular a concept as you might at first imagine. And for the record, I’m not talking about what you have to drink on your deathbed. There are lots of other last drinks: Your last drink of the night; the last pour from a treasured bottle; the last sip of a cocktail or a beer or a dram of whiskey; and that last swallow before keeling over in a college drinking game.

There’s a lot to the last drink, so let’s start with the fun one.

I do still play drinking games—even at 60. Well, one drinking game: The Boot Game. It’s involves Jenga-like strategy and poker-like people-reading skills. If you’ve never seen them, there are two-liter glasses in the shape of boots. For the game, you fill one with beer. Players sit round a table. There are various house rules, but the basics of the game are simple. As the boot circles the table, each player goes through some kind of tapping and knocking ritual, takes a drink, goes through the ritual again (usually in reverse order), and then passes the glass on. Ideally, the game is secondary to conversation or watching sports, so it’s not just a big glass of beer flying around a table.

The strategy comes in when you decide what size sip you’re going to take. The goal of the game is to avoid being the next-to-last person to take a drink before the boot is emptied, since that next-to-last person buys the next fill-up. The last drink is the winning drink, and your strategy can either be to shallowly sip to move the boot on safely...or to make a heroic, unexpected drain from above the ankle and pin the person before you. Choose carefully.

If you’re in a bar, the last drink of the night might be a bonus. There are many bars where the last ounce from a bottle, or the last foamy, splashing pour from a keg is considered a freebie. There are just as many where it is not, so don’t make the mistake of assuming or demanding your “free shot.”

In some areas, that last pour in the bottle is known as “the Spider.” Do yourself a favor: don’t look that up on Urban Dictionary. You don’t want to know what other things are called “the Spider.”

There’s a term for the last drink among the folks in the brewing industry that started in my hometown of Philadelphia. They call the one you probably didn’t need but had anyway, the TUD: the Totally Unnecessary Drink. I’ve heard people using the term as far away as Denver and Seattle, so it may be spreading.

If you’re drinking wine (or some Belgian beers), the last drink may have another name, an older name. I mean much older, as in Biblical. Here’s Isaiah (51:17), talking about draining the cup of God’s anger: “Awake, awake, stand up, O Jerusalem, which hast drunk at the hand of the Lord the cup of his fury; thou hast drunken the dregs of the cup of trembling, and wrung them out.”

The dregs are the bits of sediment that settle to the bottom of the bottle, or of the glass, so if you’re drinking them, you’re getting the very last drink. They are also called the lees (though technically the lees are specifically yeast particles), and I have a quote for that, too, not quite as old, from Tennyson’s poem, Ulysses: “I cannot rest from travel: I will drink life to the lees,” which is to say, to the very last drop.

Similarly, there’s a persistent bit of urban legend that the last sip of a beer (or any shared drink) is almost all “backwash.” That’s right: spit, saliva, washed back into the glass from the drinkers’ mouths. Or “drinker’s mouth,” since if everyone’s doing it, so are you. Yuck, right?

Relax, I did say “urban legend.” If you really think about it, there’s just not that much saliva in our mouths at any given time that even the sloppiest drinker could get that much into a glass. That last sip of beer may taste different, flat, insipid, but that’s because it’s probably much lower in carbonation than when it was first poured, and warmer. If you have that problem a lot, maybe think about using a smaller glass.

That neatly brings me to the last drink that was the inspiration for this story: the last sip of a cocktail. There’s a folk myth, a party tale, a bit of bar lore that the last sip of a drink is the strongest one. I’ve experienced that with a cup of sweet tea, in which the last drink was heavily sugared, but always figured that the last sip of a mixed drink was the weakest, what with the dilution of ice melt.

But part of the fun of this job is the latitude to ask serious scientists silly questions. So I got in touch with Dr. Gary Spedding, the head of Brewing and Distilling Analytical Services, LLC in Lexington, Kentucky. He tests the alcohol level of drinks all day long. I asked him if the last drop of a drink could be stronger.

“There has been a lot of research about the strength of alcohol and the forcing into solution of congeners as clusters—depending on that alcohol concentration,” he began, and I knew I was in trouble. But I soon realized that Spedding wasn’t talking about the alcohol level being stronger. He was talking about the flavors and aromas being stronger—or changing—at the end.

“I often get diacetyl (a fermentation by-product that smells buttery) in some samples, only with the last drop,” he said, “so there is something to this. Think about when you open up a spirit by adding a few drops of water—a reduction in alcohol strength allows more volatiles (of some kinds) to leave solution sequestration and volatilize. Others may get pushed into clusters and not be as available for detection, of course.”

“This could be what is going on in the last drop,” he mused. “The alcohol will be evaporating fast as that last drop warms up leaving water and heavier, less volatile molecules behind. So when one molecule has gone—the ethanol—they can come out into view, so to speak. While this all seems a bit speculative, I think it’s sound in principle. It certainly seems to work in practice.”

Who am I to argue with the good doctor? So, excuse me, I have some last drops to finish in my whiskey glass.

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