Espresso: Definition, Numbers, and What Actually Matters

Espresso is the smallest serving of coffee with the biggest impact – and at the same time the drink people talk the most nonsense about. That the crema reveals the quality. That it's especially high in caffeine. That there's exactly one right way to make it. This article sorts out what can be backed up and what can't.

And because that's part of who we are: there are no espresso police. The numbers below are guidance, not a verdict. If your espresso tastes better to you longer, shorter or with sugar, that's your right cup.

What is an espresso?

An espresso is a short, concentrated coffee made by forcing hot water at high pressure through finely ground coffee. Around 25 to 35 millilitres end up in the cup, topped with a hazelnut-brown layer of foam: the crema. The decisive difference from filter coffee isn't the bean but the pressure – and the short contact time that follows from it.

Linguists don't agree on where the name comes from. Some derive “espresso” from the Italian “esprimere” – “to press out”, from Latin exprimere, a reference to the brewing pressure. Others link it to the English “express”, as in express train, an image the first machines around 1900 used in their advertising. Only the practice behind it is certain: these machines brewed each cup specifically for the individual order instead of in large batches in advance – and that was exactly the revolution.

Which figures define an espresso?

There's no internationally binding standard. What does exist is the definition of the Istituto Nazionale Espresso Italiano, which describes its certified Espresso Italiano with fixed values: 7 grams of ground coffee, 88 degrees water temperature at the outlet of the group head, 67 degrees in the cup, 9 bar water pressure, 25 seconds extraction time and 25 millilitres in the cup – each with a tolerance. That the 9 bar is the pressure as the water enters the ground coffee, and the 25 millilitres a volume including the crema, usually gets lost in the familiar list. And even in Italy, this isn't the only definition: the Disciplinare “Espresso Italiano Tradizionale” allows 7 to 9 grams, 20 to 27 seconds and 13 to 26 grams of beverage in the cup.

Animation 1 · Six target values, each with a permitted range

Line = permitted rangegreen = target valueblue dot moves through the range

One of several definitions – that of the Italian association INEI. It describes the simple Italian shot made from 7 g of ground coffee in a bar. All lines are the same length: they only show the range, not the magnitude. Each row has its own unit.

Where exactly it's measured: the ground coffee dry, before the water arrives · the water at the group outlet, not in the boiler · the beverage when served · the pressure as it enters the ground coffee, roughly nine times atmospheric pressure · the time from start to stop · the amount as a volume including crema, not a weight.

Note: the scale changes within this article. These 25 ml are a volume and belong to 7 g of ground coffee – the Italian single shot. Animation 3 works with an 18 g double shot and measures the beverage in grams on the scale.

Source: Istituto Nazionale Espresso Italiano, “Espresso Italiano Certificato” (association standard). It isn't even the only Italian definition: the Disciplinare “Espresso Italiano Tradizionale” allows 7–9 g, 20–27 s, at least 8 bar and 13–26 g of beverage in the cup.

These values describe the Italian bar espresso, not the only possible one. In the specialty scene, people often work with considerably more coffee – 16 to 18 grams in a double basket is standard today – and the ratio of dose to beverage is controlled deliberately. The 16 to 18 grams are a figure based on experience from the scene and from our courses, not a survey and not a standard. How we do it at the Coffee Coaching Club is explained in our article on espresso dial-in.

The 25 seconds are the most-quoted and most often misunderstood value. They're an observed value from Italian bar practice, not a target – and if you steer towards them, you end up adjusting the grind instead of paying attention to taste.

What is crema – and does it say anything about quality?

Crema is a foam made of emulsified coffee oils and carbon dioxide. Roasting produces CO₂, which stays bound in the bean; under the 9 bar of the group head it dissolves in the water and bubbles out again in the cup as the pressure drops. So what you see is essentially gas in oil.

And now the part you rarely hear: crema is not a reliable sign of quality. Above all, it tells you something about freshness and the type of bean. Canephora, commonly called Robusta, naturally produces more and more stable crema than Arabica – so an espresso with thick crema may simply contain more Canephora. Pressurised baskets also produce crema more or less at the push of a button, regardless of how the coffee tastes.

The reverse is also true: a very fresh, lightly roasted Arabica can have a thin crema that breaks up quickly and still taste excellent. Judge your espresso in your mouth, not with your eyes.

How much caffeine is in an espresso?

Considerably less than most people assume – and far less precisely than any table suggests. The reference value in the USDA nutrient database is about 63 milligrams of caffeine for a serving of espresso of around 30 millilitres, and around 94 milligrams for a regular 240-millilitre cup of filter coffee. So per millilitre, espresso clearly has more caffeine – per serving, filter coffee comes out ahead, because the cup is eight times bigger. The catch: these are averages. When researchers measured real cups in cafés, 20 espressos ranged from 51 to 322 milligrams, with an average of 140.

Animation 2 · Caffeine per serving — reference value and real-world spread

Bar = reference value from the USDA nutrient database (an average)Line = range measured in cafésAverage of the measurement series

Per millilitre, espresso has roughly five times as much caffeine: 2.1 mg versus 0.4 mg per millilitre. Per serving, it's the other way round, because the filter cup is eight times bigger than the espresso cup. The measured servings were 23 to 70 ml (2012) and 40 to 170 ml (2003).

Reference values: USDA FoodData Central – espresso 62.8 mg per 30 g, filter coffee 11.8 mg per 30 g. Measurement series: Crozier et al. 2012, Food & Function 3:30 (20 espressos) and McCusker et al. 2003, Journal of Analytical Toxicology 27:520. Both peer-reviewed, both with a very wide spread. The same filter coffee, bought on six days in the same shop: 259 to 564 mg in a 473 ml cup.

Two more things affect the value: the type of bean and the amount. Canephora contains roughly twice as much caffeine as Arabica, and a double shot with an 18-gram dose naturally delivers more than an Italian single with 7 grams. The ratio between the two species is a rough guideline from the literature – estimated, not measured by us. The figures given are averages, not a measurement of your cup.

What's the difference between ristretto, espresso and lungo?

Just one thing: how much beverage you let run from the same dose. It's always weight to weight – the dry dose in the basket to the beverage weight in the cup, both on the scale. A ristretto is stopped at roughly the weight of the dose, an espresso at double, a lungo at triple or more. Grind, bean and machine stay the same.

Animation 3 · Same dose, three beverage weights

Beverage running into the cupMeasuring cup up to 60 g

The same for all three: 18 g of dry ground coffee, same grind, same bean. The ratio 1:1, 1:2 or 1:3 means dry dose to beverage weight – both in grams on the scale, not millilitres, not volume, not cup size. All three columns start at zero grams, so the heights are directly comparable. A ristretto is dense and syrupy, 1:2 is the usual double shot, a lungo is lighter and often more bitter.

Also measured (20 g dose): 130 mg caffeine at 1:1 · 183 mg at 1:2 · 204 mg at 1:3.

Caffeine values: Schmieder et al. 2023, Foods 12(15):2871 – average of 15 test series, Arabica. 36 g of beverage is around 35 ml of liquid; the crema on top makes the cup look fuller. Change of scale from Animation 1: there a 7 g dose and 25 ml volume, here 18 g and grams.

Important: a lungo is not an espresso topped up with hot water – that would be an Americano. With a lungo, more water actually runs through the same coffee bed, and that's exactly why it often tastes more bitter: the compounds dissolved last are the unpleasant ones.

Where does espresso come from?

From Italy, but step by step. In 1884, Angelo Moriondo patented a machine that drove steam through ground coffee – though for large quantities at once. In 1901, Luigi Bezzera registered a machine that brewed individual servings using portafilters. Desiderio Pavoni bought the patents and sold the first commercial espresso machines from 1905.

These early machines worked with steam pressure and produced a bitter coffee without crema. The breakthrough came in 1947 with Achille Gaggia: his lever machine used a spring-loaded piston to force the water through the ground coffee at around 12 atmospheres – and in doing so created, for the first time, the foam that Gaggia marketed as crema caffè. So espresso as we know it today is younger than the car.

Which beans are suitable for espresso?

Basically any. “Espresso beans” aren't a separate plant but a roasting decision: roasted a little longer and darker than filter coffee, so that the aromas dissolve well under pressure in a short time and the acidity takes a back seat. The same bean can taste fruity as a filter roast and chocolatey as an espresso roast.

Classic Italian blends often contain a share of Canephora – for crema, body and a strong, earthy base note. Pure Arabica roasts, on the other hand, come across as clearer and sweeter, often with more acidity. Both are legitimate. You'll find our selection under coffee beans, and what “specialty” means here is explained in the article on specialty coffee.

What does a good espresso taste like?

The way you like it – but a few characteristics can be described independently of taste. A successful espresso is dense but not viscous, has sweetness and stays pleasantly in your mouth after you swallow. What it shouldn't be: sharply sour, harshly bitter, or thin and watery.

What you taste	Probably	First step
Sour, thin, salty	under-extracted	grind finer
Bitter, dry, harsh	over-extracted	grind coarser or stop the shot sooner
Bitter and thin at the same time	channels in the coffee bed	check your puck preparation, not the grind
Flat, no sweetness	beans too old or too fresh	check the roast date

Why does your espresso taste different at home than in a bar?

Because in a bar, three things come together that are usually missing at home: a grinder that's set to the same bean all day, a machine with a stable temperature, and a person who pulls twenty shots a day instead of one. None of it is magic, but all of it is routine.

The single biggest lever at home is the grinder. A good machine with a mediocre grinder delivers less than a mediocre machine with a good grinder. The second lever is a scale – not because grams taste better, but because it lets you repeat what worked.

Frequently asked questions about espresso

How much caffeine does an espresso have?

The reference value is around 63 milligrams for a 30-millilitre serving; a 240-millilitre cup of filter coffee comes to around 94 milligrams. Per millilitre, espresso has more caffeine; per serving, it contains less. Measured cups vary widely, though: in a study of 20 espressos from cafés, values ranged from 51 to 322 milligrams.

How much espresso is 25 ml?

About one big sip – the classic Italian serving from 7 grams of ground coffee. In the specialty scene, the double shot is the norm: a dose of 16 to 18 grams yields around 30 to 40 grams of beverage, depending on the recipe.

Is thick crema a sign of quality?

No. Crema mainly tells you something about freshness and the type of bean: Canephora produces more crema than Arabica, and pressurised baskets produce it regardless of coffee quality. An excellent light Arabica can have a thin crema.

What's the difference between espresso and lungo?

With a lungo, more water runs through the same amount of ground coffee, usually around three times the dose instead of twice. This makes the cup bigger and lighter, but often also more bitter, because mostly unpleasant compounds are dissolved at the end.

What's the difference between espresso and Americano?

With an Americano, a finished espresso is diluted with hot water. With a lungo, the extra water runs through the coffee bed. Same cup size, completely different taste – the Americano stays closer to the espresso in flavour.

Does espresso need special beans?

No, but a suitable roast helps. Espresso roasts are roasted a little longer and darker so that the aromas dissolve well under pressure during the short brewing time and the acidity takes a back seat. Light filter roasts can be prepared as espresso, but they need more fine-tuning.

Why does my espresso taste sour?

Usually it's under-extracted: the grind is too coarse or too little beverage runs into the cup. Grind one step finer and change nothing else. Not every acidity is a fault, though – light roasts naturally bring fruity acidity with them.

What next?

If you want to fine-tune your espresso, the next step is the dial-in – that's where we explain how we match grind and dose to each other. If you'd rather continue with milk, you'll find the next chapter with the cappuccino and the flat white.

And if you'd rather go through it together at the machine: that's exactly what we do in our showrooms in Bern and Zurich – in the workshops or in the barista course in Zurich. There are no espresso police. In the end, all that matters is whether you enjoy the cup. United by Coffee.

Sources

• Istituto Nazionale Espresso Italiano: L'Espresso Italiano Certificato – 7 g ± 0.5 ground coffee, 88 °C ± 2 at the outlet of the group head, 67 °C ± 3 in the cup, 9 bar ± 1 water pressure on entry, 25 s ± 5 extraction time, 25 ml ± 2.5 in the cup including crema. For comparison, the Disciplinare Caffè Espresso Italiano Tradizionale (2018): 7–9 g, 90–96 °C, at least 8 bar, 20–27 s, 13–26 g in the cup.
• Caffeine reference values: USDA FoodData Central (espresso 62.8 mg per 30 g; filter coffee 11.8 mg per 30 g). Measured spread: Crozier, Stalmach, Lean & Crozier (2012), Espresso coffees, caffeine and chlorogenic acid intake, Food & Function 3:30 – 20 espressos from cafés, 51 to 322 mg per serving, median 140 mg; McCusker, Goldberger & Cone (2003), Caffeine content of specialty coffees, Journal of Analytical Toxicology 27:520 – espresso 58 to 185 mg, the same filter coffee on six days 259 to 564 mg in a 473 ml cup.
• Caffeine by brew ratio: Schmieder, Pannusch, Vannieuwenhuyse, Briesen & Minceva (2023), Influence of Flow Rate, Particle Size, and Temperature on Espresso Extraction Kinetics, Foods 12(15):2871 – from a 20 g dose, 130 mg caffeine at 1:1, 182.6 mg at 1:2 and 204 mg at 1:3.
• On the history (Moriondo 1884, Bezzera 1901, Pavoni from 1905, Gaggia 1947) and on caffeine content and the composition of crema: compiled in the article Espresso, English Wikipedia, with the references given there.
• On the etymology: linguists don't agree. Etymological dictionaries (including Etymonline, Dictionary.com) derive “espresso” from the Italian “esprimere” – “to press out” (Latin exprimere); the German-language Wikipedia entry Espresso, on the other hand, traces it back to the English “express” for an express train. That's why we don't present any single origin as certain in the text.