Why Does Liquor Come in Fifths?

Why does liquor come in fifths? —AA OCD

Readers sometimes complain that “Dr. Know” should be called “Dr. Doesn’t Know but Will Google It.” I resent the implication that I merely regurgitate the results of web searches anyone could perform. (I don’t deny it, but I resent it.) You might suppose that this week’s question is a perfect example of this—a simple query any idiot with an internet connection could answer in 10 seconds. Nope! It actually took several hours (not to mention a specially trained idiot).

This is not to say that Google provides NO answers. One source notes that “the reason it’s called a fifth is because it’s one-fifth of a U.S. gallon.” (Thanks, Dr. Hawking.) Another says Depression-era distillers switched from quarts to fifths as a form of shrinkflation. Yet another claims the standard “represents the average lung capacity of a glass blower,” which strikes me as utter horseshit.

And yes, pedants, I know the modern standard is 750 ml—but that size was chosen because it closely resembled the fifth already in use. How did one-fifth—not a widely used fraction—become the default for liquor and wine?

The fifth appears to be descended from a British measure called a “reputed quart,” mentioned in various documents from the 1700s onward. Like the fifth, the reputed quart held around 26 ounces. But what was this quart a quarter of? Did the Brits have a different gallon?

Actually, they did—unfortunately, the imperial gallon was larger than ours, which is the wrong direction. In any case, the short quart predates the imperial gallon by several decades. Indeed, its roots go all the way back to the 1200s, when the Tractatus de Ponderibus et Mensuris (“Treatise on Weights and Measures”) defined an ounce as the weight of 640 grains of wheat. From there: “Twelve Ounces make a Pound, and Eight Pounds make a Gallon of Wine.”

So wait—is a gallon the volume of 8 pounds of wheat or 8 pounds of wine? The wheat interpretation is what ultimately caught on—but not before glassblowers got used to making quart bottles based on the wine version. That wine-derived gallon turns out to be four-fifths the size of our gallons, making a wine-derived quart equal to a modern fifth.

Everybody knew these weren’t real quarts, hence the modifier “reputed,” which literally means “so-called” and basically puts scare quotes around every bottle. And yet we still use them today! Shows what you can accomplish when you’re full of booze.

Questions? Send them to dr.know@wweek.com.