The crema. For many, it's the crowning glory of espresso. Many swear that good crema means good coffee, that tiger stripes give espresso that final kick, and no crema indicates bad espresso. Well, unfortunately, it's not that simple.
For many, the foam (Italian: crema) on coffee is indispensable. There is hardly an image, hardly a coffee package, hardly a coffee advertisement that doesn't feature coffee topped with foam. You almost get the feeling that foam must be part of coffee, otherwise something isn't right. Yes, that the foam is just as important as the drink itself.
I admit, the foam simply looks really good. We have become so used to it that we believe crema simply has to be there, no matter what the drink.
Based on these observations, opinions and even theories are formed that become so strong that the preparation of the perfect espresso, the often-cited God Shot, seems unattainable. And an entire industry capitalized on this – the most beautiful foam suggests the best coffee.
One thing is clearly shown: espresso is probably the drink with the most expression, the most myth, the highest attractiveness. And crema is partly responsible for that.
What is Crema?
Crema is a foam that only forms because we work with high pressure and high temperatures. Hot water of more than 90° hits ground coffee with high pressure of +/- 7 bar. The water emulsifies the oils in the coffee powder, while the CO2 in the coffee is dissolved by these high temperatures and pressure. As soon as the coffee exits the sieve, the coffee emulsion moves from a high-pressure environment to an atmospheric-pressure environment. As the pressure on the emulsion decreases, the trapped CO2 expands and turns into foam.
It's somewhat similar to a shaken soda bottle. We all know that if you shake a soda bottle vigorously and then open the lid immediately, you'll be covered in a soda fountain: a liquid with CO2 in a high-pressure environment enters a lower-pressure environment, creating foam.
Crema is nothing more than a special type of foam. The foam consists of two phases: the continuous phase, i.e., the medium in which the CO2 gas bubbles are present as a dispersion. This means that they do not dissolve in the continuous phase.
It just looks really good.
The Short Lifespan of Crema
The lifespan of crema is up to 40 minutes. And within these 40 minutes, its structure changes considerably. Liquid, fine-pored foam eventually becomes dry, porous foam. However, this is not really important for many consumers, as espresso is usually drunk quickly.
Crema diminishes because its molecular structure slowly changes. This happens with any foam when drainage occurs. The heavier oil particles sink because they are attracted by gravity. This changes the crema's structure, making it unstable and gradually dissolving.
Literature tips and other videos
Here you will find two scientific analyses on the topic that we can recommend:
Xiuju Wang, 2014:
Understanding the Formation of CO2 and Its Degassing
Behaviours in Coffee
Illy and Navarini, 2011:
Neglected Food Bubbles: The Espresso Coffee Foam
James Hoffmann's video on the topic goes even deeper into the chemical composition of crema and touches on its historical origin.
5 Factors Influencing the Amount of Crema
From the first step, we understand that crema is just a type of foam. We will discuss here which factors determine the quantity and quality of this foam.
Crema and CO2
The gas bubbles in the crema are dissolved CO2. But where does it come from, and which coffees contain more CO2?
CO2 is produced as a byproduct during coffee roasting. The CO2 then deposits in the cell structure of the roasted coffee beans. For a foam to appear on the coffee, the CO2 must remain stored in the bean. This requires airtight packaging, timely grinding, and a correctly adjusted grinder.
The Roast Age
The fresher a coffee is, the more crema it will have. The older it is, the less crema will be present because the CO2 has evaporated. Similarly, the crema-clock starts ticking as soon as a package has been opened.
Crema is therefore a good indicator of the age of a roast. Espressos reach their best enjoyment time around two to three weeks after roasting. After around two to three months, the quality of the roast decreases. The crema indicator can therefore certainly provide a hint as to whether a coffee is relatively fresh. From this, quality can be deduced based on freshness.
The Degree of Roast
Different roast levels result in different crema volumes. There is a high correlation between foaming abilities and fractions that have a high molecular weight of complex sugars and proteins, all of which are caused by Maillard reactions.
During roasting, coffee enters the Maillard reactions at 140°C, which are non-enzymatic browning reactions. This means that the coffee turns brown but doesn't really taste like coffee yet.
As the temperature increases, Maillard reactions also increase. Reducing sugars form new compounds with amino acids and begin to create the coffee's aromas.
Back to foamability, which is positively influenced by pronounced Maillard reactions. If a coffee is roasted longer, and thus spends more time in the Maillard phases, more crema is produced in the cup.
The Water
An invisible factor that can influence crema is water. Perhaps you've noticed that the same coffee foams more in one place and less in another.
Hard water tends to create a little more foam, while soft water produces less foam. This is true for soap as well as for coffee foam.
The Machine Types
Although we speak of the crema, there are significant differences in consistency, porosity, and elasticity.
| Espresso from a portafilter machine | usually results in a dense, elastic, glossy crema |
| Espresso with a bottomless portafilter | yields a voluminous, rich crema, as the coffee stream is not redirected. Thus, the intact crema goes directly into the cup. |
| Espresso from an automatic coffee machine | results in a voluminous, but less elastic crema. It is more porous because it traps more air. |
| Filter coffee | produces no crema, as the pressure during extraction is too low |
| Capsule coffee | often produces a very airy crema, less elastic, but voluminous |
| Moka pot | produces little stable foam, as the ratio of water to coffee is large. |
| Cezve/Ibrik | produces only a little foam, as it is prepared without pressure |
The crema from a fully automatic coffee machine is very voluminous, but fluffier and somewhat drier than the crema from a portafilter machine.
Focus: The Crema of Coffee Capsules
Capsule coffee produces a lot of foam. Contrary to rumors that baking powder or some other agent is present, there is a simple explanation.
- lots of gas in a small space
- on average, about 5.5g of roasted coffee is pressed into a capsule. The coffee is usually ground and encapsulated immediately after roasting. Thus, the CO2 flows into the capsule and remains trapped there. Often, the coffee capsule is also filled with nitrogen, which displaces the last oxygen.
- Relative to the small amount of coffee, the coffee capsule contains a lot of gas, which foams up during extraction.
- larger holes without resistance
- when the capsule is punctured by the filter plate, the coffee shoots out of the capsule through relatively large outlet holes without resistance
- the fast flow is not redirected (= slowed down) and lands directly in the cup
The information comes from Patrizio Frigeri, coffee engineer, who has also reported extensively on capsules here.
For many, a reason to buy a capsule machine: the foolproof foam on the coffee.
More Robusta = More Foam
Often, for more classic espresso interpretations, an intense foam is desired – even a small amount of Robusta can help achieve this goal. 100% Robusta is extremely foamy; the spouts of the portafilter almost overflow during extraction. However, the foam's consistency is different; it is more porous, somewhat drier, less shiny, and less elastic.
Why?
Robusta, especially in medium-dark roasts, has up to twice as much CO2 as Arabica coffees. And: Robusta has only about half as much fat in the form of oils as Arabica – and we know that oil does not foam. In other words: the oils in Arabica prevent more intense foam formation.
Is Crema Overrated?
In one of the classics of coffee books, it states that for a "proper espresso", at least 10% of the drink must be crema.
I find it difficult to accept such rigid definitions for a beverage that is consumed worldwide and interpreted with different perceptions of coffee.
10% crema volume is primarily an optical reason – if there were only a thin layer of crema on the liquid, we might think that the coffee is old, or that it was poorly prepared.
If appearance seems so important, then we can also ask if espresso is a multi-sensory drink? Do the cup, the spoon, and the glass of water also belong? Probably, because espresso is always a brief moment of enjoyment.
Tiger stripes espresso from our Facebook Community. Left by Marco Rödel, right by Olaf Sühr.
The Tiger Stripes on Espresso – Are They Important?
Nevertheless, we are strongly influenced by the idea that the crema should be amply present. And it should be beautiful – we constantly hear about tiger stripes, which are supposed to suggest a particularly well-executed extraction.
Tiger stripes are nothing more than fine coffee particles that detach during extraction. However, tiger stripes do not appear equally – or at all – in all coffees.
- especially with darker coffees, tiger stripes are often visible, because darker coffees are more brittle due to the high roasting temperatures.
- in the vast majority of cases, tiger stripes appear with conical grinders that produce more fines. Daniel Hofstetter explains this clearly in this video.
The Barista Championships and the Crema-(R)Evolution
The harsh visual assessment and the supposed influence on taste were long overestimated – and this also at the World Barista Championships. In the early days and deep into the 2000s, crema accounted for 50% of the total score in the espresso category. Fifty percent. The other half was for taste – almost unimaginable from today's perspective.
"Back then" they would stare for a long time, tilt the cup, assess the elasticity, judge the hopefully reddish-brown color, and note the absence of bubbles.
Felix Hohlmann at the Swiss Barista Championship 2017. At that point, it was only noted whether the crema was present or not.
Imagine that today – almost impossible. And yet that was the standard until just over 12 years ago. And today, the crema's appearance counts for less than 2%. Thank God.
We kindly received this information from Sonja Björk Grant and Gloria Pedroza, two long-standing judges at World Barista Championships.
And that brings us to the most important question for us: is crema delicious? And does crema make espresso better?
- Crema is an indicator that the extraction was certainly not too fast or too slow, but even then, I still don't know if the coffee will taste good.
- We tasted the crema, and only the crema. Crema alone tastes bitter. And you can feel the CO2. It has an unpleasant acidity, almost like carbonic acid.
- An espresso without crema is less roasty because it contains less CO2, as this is primarily present in the crema.
Whether you prefer coffee with or without crema is up to you. Try extracting two espressos. Remove the crema from one cup with two spoons, and mix it into the other. The coffees will taste distinctly different.
So. Crema is somehow part of it, mainly for optical reasons, because we have internalized this espresso drink so visually.
More crema is not better, and no crema does not necessarily mean the coffee is bad.
