<p>This seems like the fur to me. I believe the water hardness is more than it is normally used.</p>
<p>As we know that calcium carbonate (or others that lead to water hardness) is a bit distinct salts among others as they dissolve less with temperature.</p>
<p>Very probably this thin layers of calcification occurred when your cup is hot at first, but obscured by the foam. When foam disappears the thin layer of calcification becomes visible.</p>
<p>To test, try to remake coffee with softened water. To soften, boil and cool down the water, first.</p>

CC BY-SA 4.0
2024-11-11T20:38:56.763Z
2024-11-11T20:38:56.763Z
MTSan
<p>It is a reaction between the coffee and the relatively cold air in contact with it.  If you compare the coffee to clouds, the &quot;scum&quot; is gasses condensing and expanding on the surface of the coffee like how clouds form because it is extremely cold 10-20-30,000 feet up compared to the ground.</p>
<p>edit: the first photo is what i explained above, the second photo does indeed look like oils from the beans.</p>

CC BY-SA 4.0
2024-11-11T19:53:56.187Z
2024-11-11T19:54:53.863Z
2024-11-11T19:54:53.863Z
Rusty Shackleford
<p>It is just oil from the coffee beans. Nothing to be afraid of unless your coffee tastes off. You can stir the coffee to try and reincorporate the oil or use spoons to skim off the oil from the top</p>

CC BY-SA 4.0
2020-04-18T00:58:04.423Z
2020-04-18T00:58:04.423Z
Austin Mehmet
<p><a href="https://i.sstatic.net/jy4yf.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/jy4yf.jpg" alt="Coffee with white stuff floating in it"></a></p>

<p>Hello, Lately my coffee seems to have a film on the top. The picture makes it look a lot worse then it is. It is more translucent in the cup. This happens once the coffee gets cold. When its hot it looks like bubbles or just the oil from the coffee beans.</p>

<p>What is this? Is this just the oil from the coffee? Or do I need to clean my machine?</p>

<p>Coffee Details:</p>

<ul>
<li>Black Coffee, nothing added.</li>
<li>Made in espresso machine.</li>
<li>Ground to order.</li>
<li>Run through several times as I "overpacked" the coffee. </li>
<li>Hot water added to make Americano. </li>
<li>Beans from local roaster, last week.</li>
</ul>

<p>This is what my coffee looks like before it turns into that:
<a href="https://i.sstatic.net/9e0W5.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/9e0W5.jpg" alt="enter image description here"></a> </p>

CC BY-SA 4.0
2020-03-28T18:51:07.040Z
Do you use a fresh _cup_? (Serious question, some coffee drinkers insist on never washing their cups with soap.) Has anything else changed? Welcome to Coffee SE, btw.!
Stephie
CC BY-SA 4.0
2020-03-28T21:44:27.647Z
Yes I washed my cup before I filled it. I'm not sure if I used soap I might have just rinsed it out to look clean. Thanks!
marsh
CC BY-SA 4.0
2020-03-29T04:12:31.283Z
If it happens consistently, you can try a series of experiments one at a time, e.g. clean the grinder, use bottled water, clean the espresso machine, vary the packing pressure, ...
Jerry101
CC BY-SA 4.0
2020-03-30T14:42:08.053Z
I am fairly certain its just the crema. I made a fresh cup with plenty of crema and slowly saw it melt away into what I see.
marsh
CC BY-SA 4.0
2020-04-28T17:22:14.343Z
By scum do you means the best part of espresso?!
SaggingRufus
CC BY-SA 4.0
2020-05-01T14:54:43.077Z
@SaggingRufus I mean? Maybe? I like the crema but I havent seen this at coffee from shops.
marsh
<ground-coffee><coffee-machines><cleaning>
What is this scum in my coffee
marsh
# What is this scum in my coffee

(Asked by: username_0 on 2020-03-27)

[![Coffee with white stuff floating in it](https://i.sstatic.net/jy4yf.jpg)](https://i.sstatic.net/jy4yf.jpg)

Hello, Lately my coffee seems to have a film on the top. The picture makes it look a lot worse then it is. It is more translucent in the cup. This happens once the coffee gets cold. When its hot it looks like bubbles or just the oil from the coffee beans.

What is this? Is this just the oil from the coffee? Or do I need to clean my machine?

Coffee Details:

* Black Coffee, nothing added.
* Made in espresso machine.
* Ground to order.
* Run through several times as I "overpacked" the coffee.
* Hot water added to make Americano.
* Beans from local roaster, last week.

This is what my coffee looks like before it turns into that:
[![enter image description here](https://i.sstatic.net/9e0W5.jpg)](https://i.sstatic.net/9e0W5.jpg)

**Tags:** ground-coffee, coffee-machines, cleaning

> **Comments:**
> **username_1**: Do you use a fresh _cup_? (Serious question, some coffee drinkers insist on never washing their cups with soap.) Has anything else changed? Welcome to Coffee SE, btw.!  
> **username_0**: Yes I washed my cup before I filled it. I'm not sure if I used soap I might have just rinsed it out to look clean. Thanks!  
> **username_2**: If it happens consistently, you can try a series of experiments one at a time, e.g. clean the grinder, use bottled water, clean the espresso machine, vary the packing pressure, ...  
> **username_0**: I am fairly certain its just the crema. I made a fresh cup with plenty of crema and slowly saw it melt away into what I see.  
> **username_3**: By scum do you means the best part of espresso?!  
> **username_0**: @username_3 I mean? Maybe? I like the crema but I havent seen this at coffee from shops.  

---

## 3 answers

### Answer by username_6 on 2020-04-18. Score: 2 | Accepted answer

It is just oil from the coffee beans. Nothing to be afraid of unless your coffee tastes off. You can stir the coffee to try and reincorporate the oil or use spoons to skim off the oil from the top


---

### Answer by username_4 on 2024-11-11. Score: 1

This seems like the fur to me. I believe the water hardness is more than it is normally used.

As we know that calcium carbonate (or others that lead to water hardness) is a bit distinct salts among others as they dissolve less with temperature.

Very probably this thin layers of calcification occurred when your cup is hot at first, but obscured by the foam. When foam disappears the thin layer of calcification becomes visible.

To test, try to remake coffee with softened water. To soften, boil and cool down the water, first.


---

### Answer by username_5 on 2024-11-11. Score: 0

It is a reaction between the coffee and the relatively cold air in contact with it. If you compare the coffee to clouds, the "scum" is gasses condensing and expanding on the surface of the coffee like how clouds form because it is extremely cold 10-20-30,000 feet up compared to the ground.

edit: the first photo is what i explained above, the second photo does indeed look like oils from the beans.


---

