We are not sure. Or at the very least - nobody seems to agree.

Perhaps we should ask the people that first invented it - the Italians.

The classic Italian definition from the Istituto Nazionale Espresso Italiano says a "single" espresso is:

Necessary portion of ground coffee = 7 g ± 0.5

Exit temperature of water from the unit = 88°C ± 2°C

Temperature of the drink in the cup = 67°C ± 3°C

Entry water pressure = 9 bar ± 1

Percolation time = 25 seconds ± 2.5 seconds

Viscosity at = 45°C > 1.5 mPa s

Total fat = > 2 mg/ml

Caffeine = 100 mg/cup

Millilitres in the cup (including foam) = 25 ml ± 2.5

In North America we tend to use a mishmash of metric and Fahrenheit measures so this would translate to:

6.5g - 7.5g coffee is used to make less than an ounce of espresso exiting [from the spout?] at a temperature of 187F - 194F in 22.5 seconds to 27.5 seconds.

It is interesting to note that 22.5ml is only about 3/4th of 1 U.S.ounce - and that's including the crema!

Contrast the above classical Italian definition of espresso to the U.S standard, where as one might guess - the term "supersize me" takes on new significance.

So who defines what espresso is in America? This falls under the auspices of the Specialty Coffee Association of America (SCAA).

Oddly enough, I could not find the SCAA definition of espresso on their website, however the following is the one most quoted:

"Espresso is a 45ml (1.5 ounces) beverage that is prepared from 7-9 grams of coffee through which clean water of 192F - 198 F (88C - 92C) has been forced at 9-10 atmospheres of pressure, where the grind of the coffee has made the brewing "flow" time approximately 22-28 seconds."

Therefore. in America, an espresso could be twice the size of an Italian espresso.

A double shot by SCAA standards, would be an astonishing 3 fluid U.S. ounces.

"Supersize me" indeed.  

To make matters even more confusing, I've seen many other definitions at various other coffee websites.

All different.

So what is the definition of espresso?

Even for the pros, it could very well be:"Don't know - haven't the foggiest idea."

Glenn lives and works in Waterloo, Ontario as a senior financial analyst and investor. He is one of the CoffeeCrew's most prolific writers and is quickly becoming an authority on all things bean and caffeine. illy and Rancilio gear photo and concept by Colin - canon A60