Is it Espresso or Expresso? Yes
If you're trying to win your argument, you've come to the wrong place.
At Merriam-Webster, we believe that coffee is the greatest invention in the world, perhaps short of the printing press. (The Internet loses a few points because of YouTube comments.) The energy boost provided by a well-timed cup of espresso is what gets our lexicographers through the livelong day.
Only, it seems, not everybody agrees on how to spell it.
Espresso is defined as "coffee brewed by forcing steam or hot water through finely ground darkly roasted coffee beans." In the past, the term has variously referred to the machine used for preparing said coffee or the establishment where said coffee is prepared and sold. In Italian, this coffee is known as caffè espresso, or just espresso for short.
Both terms were borrowed into English:
They were the ones who had bought the silver caffe espresso urn and later the television, and they arranged the pizza parties and had the girls down…
Bernard Malamud, The Magic Barrel, 1958
And sometimes when I am walking down the King's Road or sipping my espresso in the morning—feeling, not old exactly, but fusty and adult—and chance to remember the island, immediately all things are possible.
Muriel Spark, Robinson, 1958
A Turin-born inventor, Angelo Moriondo, was awarded the patent for "[n]ew steam machinery for the economic and instantaneous confection of coffee beverage" in 1884, but the term espresso wasn't used until later, after the machine had been perfected by Luigi Bezzerra and Desiderio Pavoni.
By the middle of the twentieth century, around the time a café owner named Achille Gaggia patented the first modern espresso machine for commercial use (and the first that produced the crema that we associate with espresso today), the term espresso made its way into English.
Because of the similarity of espresso to the English word express—and the promise of coffee being prepared with relative swiftness in contrast to percolating devices, it naturally caught on for espresso to be interpreted as expresso—reflecting the "express" nature of delivery—and consequently spelled as such. Espresso machines operated faster than percolators, delivering the coffee to the customer at a speed requiring less of a wait.
Montreal night-life can be inexpensive or costly. If you care to budget severely there are coffee houses where a cup of expresso costs only 15 cents.
Charles J. Lazarus, The New York Times, 27 Nov. 1955
Expresso was regarded as a misspelling by usage experts, who scoffed at the deviation from the original Italian. Those experts were emboldened in their disapproval for the spelling by an early theory surrounding the word's etymology. The espresso in caffè espresso, it was believed, pertained not to the "express" nature of brewing but the fact that the coffee was "pressed out," espresso being cited as a past participle of esprimere, from Latin exprimere. But, as it turns out, there's a problem with that reasoning.
Exprimere is an ancestor of our word express and does indeed mean, among other things, "to press or squeeze out" in Latin. The English verb express means, among other things, "to force out (something, such as the juice of a fruit) by pressure," which accurately describes what takes place when espresso is made—hot water is forced through the grounds by way of steam pressure (approximately nine atmospheres' worth).
But it's also the case that espresso, specifically when used in Italian restaurants, has a meaning of "quickly made to order"—possibly to distinguish from brewed coffee made as a whole pot. And while the Italian esprimere does mean "express" in the sense of "to put into words" or "to make known," espresso does not mean "pressed" as those early usage commentators claimed.
That has caused etymologists to rethink the connection of espresso to the pressing out of coffee beans and back toward the method of delivery—coffee made to order "expressly" for the customer.
So does this mean we've been wrong about expresso all this time? Yes and no. Espresso remains the original borrowed word for the beverage, but expresso shows enough use in English to be entered in the dictionary and is not disqualified by the lack of an x in its Italian etymon. Just think of expresso as a quirky, jittery variant.