<p>In their <a href="https://link.springer.com/content/pdf/10.1007%2Fs11483-011-9220-5.pdf" rel="nofollow noreferrer">famous study</a> on coffee crema, Illy and Navarini states:</p>

<blockquote>
  <p>The key to interpret the several factors affecting the crema,
  seems to be the carbon dioxide content of roasted coffee in
  addition to CO2 possibly present as bicarbonate ions in the
  water ingredient. Most of the data reported in the present
  review may suggest that espresso brewing can be described
  as “a quick way to transfer carbon dioxide from roasted and
  ground coffee to a small cup by means of hot water under
  pressure”. This then leads to the facts that for espresso
  coffee, carbon dioxide has to be:</p>
  
  <ul>
  <li>generated by roasting</li>
  <li>maintained in the bean by proper packaging</li>
  <li>maintained in the ground coffee</li>
  <li>solubilized in water</li>
  <li>released into the beverage.</li>
  </ul>
  
  <p>In this framework statements such as “any error in
  grinding or in percolation, in temperature or extraction
  level, has an immediate effect on denounced by the color,
  the texture and the persistence of the foam” or “the foam is
  the signature of a well-prepared espresso” can be well
  justified. In fact, foam volume, persistence, and consistence
  are the consequences of the carbon dioxide content
  originally present in the coffee. In addition to the
  importance of carbon dioxide in espresso coffee foam, we
  believe that carbon dioxide can play a role even from a taste
  point of view. This aspect has not yet been the subject of
  investigation.</p>
</blockquote>

CC BY-SA 4.0
2018-08-20T10:22:55.890Z
2018-08-20T10:22:55.890Z
MTSan
<p>From <a href="http://en.wikipedia.org/wiki/Espresso#crema" rel="noreferrer">Wikipedia</a>:</p>

<blockquote>
  <p>The "crema" is produced by emulsifying the oils in the ground coffee into a colloid, which does not occur in other brewing methods. 
  <img src="https://i.sstatic.net/UK772.jpg" alt="enter image description here"></p>
</blockquote>

<h2>Using the right material from the start</h2>

<p>Personally, I think this definition could use some updating. Crema exists because of the freshness of the coffee, in relation to it's roast. It contains the gasses we find from roasting, such as carbon dioxide and nitrogen gasses. You will notice that if you dig up coffee that is months old and brew it as espresso, there will be little crema. Bottoml ine, if you want crema, you need fresh coffee.</p>

<h2>Extraction</h2>

<p>The other factor in producing crema, is correct extraction. If you have a poorly extracted shot of espresso, it will be primarily water, with some seriously over-extracted coffee. An even extraction will produce the highest yield of crema.</p>

CC BY-SA 3.0
2015-01-27T21:07:38.357Z
Thank you for your answer. Can you elaborate on what you mean by an even extraction? Does that include the coarseness of the grounds?
Alex A.
CC BY-SA 3.0
2015-01-27T21:09:55.847Z
If you read my answer about [tamping](http://coffee.stackexchange.com/questions/5/how-important-is-tamping-coffee-for-an-espresso-machine/8#8), I talk about even extractions, and physics dictating that water will take the path of least resistance.
John Snow
CC BY-SA 3.0
2015-01-27T21:13:17.703Z
I did read that answer. Perhaps this is just an artifact of my limited knowledge, but I don't see how the properties of the grind play into that. It seems to be more about tamping (which is helpful--thanks).
Alex A.
CC BY-SA 3.0
2015-01-27T21:18:43.477Z
The eveness of extraction is unrelated to the coarseness of the grind.
John Snow
CC BY-SA 3.0
2015-01-27T21:22:15.233Z
Is coarseness related to crema?
Alex A.
CC BY-SA 3.0
2015-01-27T21:33:20.047Z
Crema derives from the extraction, without being ground, there would be little extraction. It is the off-gassing of brewed coffee. For this reason any ground coffee will produce crema. In larger brewing methods, such as drip, it's referred to as the bloom, and usually settles before the coffee is ready to serve.
John Snow
CC BY-SA 3.0
2015-01-27T22:19:07.103Z
I realize that it needs to be ground, I'm wondering if there's a relationship like finer ground means more crema, for example.
Alex A.
CC BY-SA 3.0
2015-01-27T21:04:31.483Z
2015-01-27T21:04:31.483Z
John Snow
<p>For a given coffee and roasting method, what factors of the espresso making process affect the crema and in what way(s) do they affect it? By my own empirical evidence, I would guess that time since grinding, coarseness of the grind, and tamping pressure are the biggest factors.</p>

<espresso><crema>
What factors affect espresso crema?
Alex A.
# What factors affect espresso crema?

(Asked by: username_0 on 2015-01-27)

For a given coffee and roasting method, what factors of the espresso making process affect the crema and in what way(s) do they affect it? By my own empirical evidence, I would guess that time since grinding, coarseness of the grind, and tamping pressure are the biggest factors.

**Tags:** espresso, crema


---

## 2 answers

### Answer by username_2 on 2015-01-27. Score: 5

From [Wikipedia](http://en.wikipedia.org/wiki/Espresso#crema):

> The "crema" is produced by emulsifying the oils in the ground coffee into a colloid, which does not occur in other brewing methods.
> ![enter image description here](https://i.sstatic.net/UK772.jpg)

## Using the right material from the start

Personally, I think this definition could use some updating. Crema exists because of the freshness of the coffee, in relation to it's roast. It contains the gasses we find from roasting, such as carbon dioxide and nitrogen gasses. You will notice that if you dig up coffee that is months old and brew it as espresso, there will be little crema. Bottoml ine, if you want crema, you need fresh coffee.

## Extraction

The other factor in producing crema, is correct extraction. If you have a poorly extracted shot of espresso, it will be primarily water, with some seriously over-extracted coffee. An even extraction will produce the highest yield of crema.

> **Comments:**
> **username_0**: Thank you for your answer. Can you elaborate on what you mean by an even extraction? Does that include the coarseness of the grounds?  
> **username_2**: If you read my answer about [tamping](http://coffee.stackexchange.com/questions/5/how-important-is-tamping-coffee-for-an-espresso-machine/8#8), I talk about even extractions, and physics dictating that water will take the path of least resistance.  
> **username_0**: I did read that answer. Perhaps this is just an artifact of my limited knowledge, but I don't see how the properties of the grind play into that. It seems to be more about tamping (which is helpful--thanks).  
> **username_2**: The eveness of extraction is unrelated to the coarseness of the grind.  
> **username_0**: Is coarseness related to crema?  
> **username_2**: Crema derives from the extraction, without being ground, there would be little extraction. It is the off-gassing of brewed coffee. For this reason any ground coffee will produce crema. In larger brewing methods, such as drip, it's referred to as the bloom, and usually settles before the coffee is ready to serve.  
> **username_0**: I realize that it needs to be ground, I'm wondering if there's a relationship like finer ground means more crema, for example.  

---

### Answer by username_1 on 2018-08-20. Score: 2

In their [famous study](https://link.springer.com/content/pdf/10.1007%2Fs11483-011-9220-5.pdf) on coffee crema, Illy and Navarini states:

> The key to interpret the several factors affecting the crema,
> seems to be the carbon dioxide content of roasted coffee in
> addition to CO2 possibly present as bicarbonate ions in the
> water ingredient. Most of the data reported in the present
> review may suggest that espresso brewing can be described
> as “a quick way to transfer carbon dioxide from roasted and
> ground coffee to a small cup by means of hot water under
> pressure”. This then leads to the facts that for espresso
> coffee, carbon dioxide has to be:
>
> * generated by roasting
> * maintained in the bean by proper packaging
> * maintained in the ground coffee
> * solubilized in water
> * released into the beverage.
>
> In this framework statements such as “any error in
> grinding or in percolation, in temperature or extraction
> level, has an immediate effect on denounced by the color,
> the texture and the persistence of the foam” or “the foam is
> the signature of a well-prepared espresso” can be well
> justified. In fact, foam volume, persistence, and consistence
> are the consequences of the carbon dioxide content
> originally present in the coffee. In addition to the
> importance of carbon dioxide in espresso coffee foam, we
> believe that carbon dioxide can play a role even from a taste
> point of view. This aspect has not yet been the subject of
> investigation.


---

