What Is Crema? Foam, CO2 and Why More Is Not Automatically Better

Crema gets more attention than any other part of a shot, mostly because it's the part you can see. Italy's espresso institute, INEI, describes it as a hazelnut-colored froth with a fine, tight texture, and it counts that froth in the cup volume. That is a fair description of what it looks like. What it means is a different question, and the best answer we found is a 2011 review by Illy and Navarini in Food Biophysics. Most of this page draws on it. Both authors are listed under illycaffè, so a coffee company wrote it, and they say the measuring methods have never been standardized.

What crema is made of

Crema is a foam. Roasting produces CO2, which stays in the beans. Grinding and brewing release it, and the bubbles end up trapped in a thin film of coffee liquid. The review calls CO2 content the key to understanding the many things that affect crema. Foam volume and foam weight both track it closely.

A foam that is already falling apart

The review describes crema as metastable. It starts as a wet, bubbly layer and turns into a drier foam as it ages, until the liquid below shows through. It reports espresso lipids as foam-negative: they appear to weaken the film around each bubble. So crema is a balance between gas that builds foam and fats that break it down.

10%

Minimum foam share of the cup volume, an older benchmark cited in the review

0.40–0.60 g/mL

Reported foam density, so it weighs far less than the liquid below

2+ minutes

How long it should last before a dark spot appears, per the review

88–98 °C

Water temperature range with no significant effect on foam volume

What changes it

Don't read the pressure row as a point for high-bar machines. The 15 or 20 bar on the box is what the pump can reach. Espresso is brewed at about 9 bar, and our comparison of 15 and 20 bar covers the rest.

Most of what you see on top was made at the roaster.

Two claims worth dropping

“Robusta gives more crema.” You will see this in a lot of retail copy. The review addresses it directly: the claim that robusta is indispensable for proper crema is substantially contradicted by recent experimental data, and the authors say the idea can't be generalized. There are real differences. Pure robusta foam clung to solid surfaces in one study, the way beer foam laces a glass, and pure arabica foam didn't. Meanwhile arabica shows the “tiger skin” pattern that robusta lacks. Arabica usually holds more total lipid, so its foam may be more prone to breaking down. Those are differences in foam, not a ranking of espresso. And you don't need a bag labeled for the job. Espresso on a bag is a suggestion from the roaster. Any roasted bean can be brewed as espresso.

“More crema means a better shot.” The review reports that crema by itself is of little sensory interest, though bitterness and astringency can stand out when it is tasted alone. It also notes that higher foam volume tends to go with lower persistence, so even “better foam” isn't one thing. The authors suspect CO2 may affect taste, and they say nobody has studied that properly yet. INEI, for its part, grades the foam as one item in a longer sensory profile, next to aroma, body and the balance of sour and bitter.

Crema as a clue to the shot

Crema does have one everyday use. Breville's instruction book for the Bambino reads it together with flow and color:

Use that as a quick read, then let your scale and your tongue decide. A fast, pale shot points you to our sour espresso page, and a slow, dark one to bitter espresso. The full routine is in our dial-in guide.

Baskets complicate the picture. Breville says its dual wall baskets regulate the pressure and help the extraction regardless of grind, dose, tamp or freshness. Our reading is that foam from a dual wall basket tells you less about your coffee and technique than foam from a single wall basket does. If you want crema to work as a clue, use a single wall basket, as Breville advises for freshly ground beans.

The easy way to get more of it

If you do want more crema, the sources point to the same short list. Buy coffee with a roast date, and Breville suggests using it 5 to 20 days after that date. Grind right before the shot. Use a single wall basket once your grind can support it. Change nothing else until you have tasted the result.

Our espresso grinder guide

Where a grinder fits

Fresh grinding is the one change here that also helps your everyday espresso routine, because you can then adjust the grind to the coffee in front of you. Our espresso grinder comparison has the options, and our espresso beans page covers the bag.

Our pick: first espresso grinderAd

Breville

Breville Smart Grinder Pro

A programmable conical burr grinder with 60 settings and cradles for 50 to 54 mm and 58 mm portafilters.

Why here: Grinding fresh for each shot is the most direct way to keep the CO2 that crema depends on, and this grinder is our first pick.

Best for: A first separate grinder, especially beside a Bambino

• +60 grind settings (Breville)
• +Grind time in 0.2 second steps (Breville)
• +Portafilter cradles for 50 to 54 mm and for 58 mm (Breville)

• –Breville's page does not state the burr size
• –A hopper grinder, not built for single dosing

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Type

Electric, hopper

Burrs

Stainless steel conical

Grind settings

60

Fits

50–54 mm and 58 mm cradles

Price class

Mid-range