<p>Though I don't have any articles on the matter, I can certainly say I've found cups of coffee that I had forgotten that are only maybe a week old with mold growing in them. I'd assume it gets contaminated so quickly, because of its sugar content. It might just be a coincidence, but it seems to happen more readily with coffee that I brew over ice. I press my areopress directly over ice, I've heard this reduces the acidity. Which would make sense, as acidity usually wards off mold. I leave all of my coffee black and unsweetened, so it is not dairy or added sugars that are causing this.</p>

<p>Perhaps try variating your brewing process. I'd be especially keen on the pH. Maybe there are some spores which will not grow in environments below a certain pH.</p>

CC BY-SA 3.0
2015-07-21T17:03:37.557Z
Low molecular-weight sugars in coffee are almost totally degraded by roasting (see Redgwell and Fischer, *Coffee Carbohydrates,* Brazilian J. of Plant Phys., 165-174, 2006 at 172). Also I think that the variation of acidity in brewed coffee doesn't deter molds any more than it deters people. You *could* change the pH but I am mainly interested in molds that grow in coffee that humans would find drinkable, and whether ones other than those I mentioned ever appear. As for the time to appear--I think you are right, about a week in warm weather.
daniel
CC BY-SA 3.0
2015-07-20T21:32:32.180Z
2015-07-20T21:32:32.180Z
tsturzl
<p>I am severely allergic to Penecillium Mold. Around a year and a half ago, I began drinking coffee on a daily basis. I had my french press brewing set up perfectly to have a nice mug every day. After about 6 weeks, I had an allergic reaction. Mold spores cause a reaction in allergic people whether they're alive or dead, so the previous answerer is wrong about being dismissive about the mold being killed in the roasting process.  </p>

CC BY-SA 3.0
2018-01-06T16:08:22.500Z
2018-01-06T16:08:22.500Z
rabidbeaver
<p>This question is not about molds that affect coffee plants. I am asking about molds that grow in coffee that has been sitting for a few days or more. I did not find any scientific articles on point so I have begun to try to answer the question by observing; but I may have missed an article and someone else may know the answer already.</p>
<p>Roasting probably kills any mold in coffee beans and if molds grow in a cup of brewed coffee they come from the surrounding air. After leaving many partially-filled cups in various spaces and looking at molds that grew in them, <em>Aspergillus</em>, <em>Penicillium</em>, and <em>Aureobasidium</em> are the only molds I have seen under the microscope so far.</p>
<p>If someone has seen an authoritative article about this it would interest me. Thanks. (This is not a health issue, IMO. I'm just curious.)</p>
<p>Here is an image of dried coffee with <em>penicillium</em> growing on it (can't determine the species without testing).</p>
<p><a href="https://i.sstatic.net/BHBuV4Ez.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/BHBuV4Ez.jpg" alt="enter image description here" /></a></p>

CC BY-SA 3.0
2015-08-07T11:23:08.913Z
I think (but do not know) that molds colonize coffee before bacteria and tend to suppress the growth of bacteria. That's why I am asking about molds and not bacteria.
daniel
CC BY-SA 4.0
2024-05-31T06:37:10.983Z
This question would be better answered in a forum dedicated to (micro)biology or mycology. There are so many species of mold, that can survive in a wide range of conditions, ph, temp, the specific nutrients in coffee for an organism to make use of, etc. Fungi as a whole is notorious for being difficult to identify purely visually. Stains help, but the best way to narrow it down would be to incubate in agars set up for differential identification (half or quartered petris, one area is control others are mixed with different inhibitors or nutrients. Same way bacteria is identified/classified
Tank R.
CC BY-SA 4.0
2024-05-31T18:08:36.290Z
@TankR.: To identify species/variants requires testing, but genuses penicillium and aspergillus are often easy to identify. You can compare the image of penicillium on dried coffee above to microscopy images online. While other molds eventually appear, pen. and asp. are quick to colonize. Don't take my word for it--get a cheap microscope and have a look.
daniel
CC BY-SA 4.0
2024-06-03T06:47:38.637Z
oh I believe you, mate! I have a cheapo amscope (highly recommend the extra few dollars for the fancier illumination under the stage if anyone reading this is in the market) that I've put some time on, experimented with homemade stains, etc. You are absolutely right the given genera have different characteristics like hyphae and spore clusters and such. Its just given the wide breadth of molds and fungi out there, it can be quite a feat to nail down one specific species purely visually. Science direct has some good visual examples of the morphology for differentiating the basics though
Tank R.
CC BY-SA 4.0
2024-06-03T18:42:20.560Z
@TankR.: Am only talking about genus, not species. No one can reliably identify species visually.
daniel
<storage>
What molds grow in brewed coffee?
daniel
# What molds grow in brewed coffee?

(Asked by: username_0 on 2015-07-18)

This question is not about molds that affect coffee plants. I am asking about molds that grow in coffee that has been sitting for a few days or more. I did not find any scientific articles on point so I have begun to try to answer the question by observing; but I may have missed an article and someone else may know the answer already.

Roasting probably kills any mold in coffee beans and if molds grow in a cup of brewed coffee they come from the surrounding air. After leaving many partially-filled cups in various spaces and looking at molds that grew in them, *Aspergillus*, *Penicillium*, and *Aureobasidium* are the only molds I have seen under the microscope so far.

If someone has seen an authoritative article about this it would interest me. Thanks. (This is not a health issue, IMO. I'm just curious.)

Here is an image of dried coffee with *penicillium* growing on it (can't determine the species without testing).

[![enter image description here](https://i.sstatic.net/BHBuV4Ez.jpg)](https://i.sstatic.net/BHBuV4Ez.jpg)

**Tags:** storage

> **Comments:**
> **username_0**: I think (but do not know) that molds colonize coffee before bacteria and tend to suppress the growth of bacteria. That's why I am asking about molds and not bacteria.  
> **username_1**: This question would be better answered in a forum dedicated to (micro)biology or mycology. There are so many species of mold, that can survive in a wide range of conditions, ph, temp, the specific nutrients in coffee for an organism to make use of, etc. Fungi as a whole is notorious for being difficult to identify purely visually. Stains help, but the best way to narrow it down would be to incubate in agars set up for differential identification (half or quartered petris, one area is control others are mixed with different inhibitors or nutrients. Same way bacteria is identified/classified  
> **username_0**: @TankR.: To identify species/variants requires testing, but genuses penicillium and aspergillus are often easy to identify. You can compare the image of penicillium on dried coffee above to microscopy images online. While other molds eventually appear, pen. and asp. are quick to colonize. Don't take my word for it--get a cheap microscope and have a look.  
> **username_1**: oh I believe you, mate! I have a cheapo amscope (highly recommend the extra few dollars for the fancier illumination under the stage if anyone reading this is in the market) that I've put some time on, experimented with homemade stains, etc. You are absolutely right the given genera have different characteristics like hyphae and spore clusters and such. Its just given the wide breadth of molds and fungi out there, it can be quite a feat to nail down one specific species purely visually. Science direct has some good visual examples of the morphology for differentiating the basics though  
> **username_0**: @TankR.: Am only talking about genus, not species. No one can reliably identify species visually.  

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## 2 answers

### Answer by username_2 on 2015-07-20. Score: 1

Though I don't have any articles on the matter, I can certainly say I've found cups of coffee that I had forgotten that are only maybe a week old with mold growing in them. I'd assume it gets contaminated so quickly, because of its sugar content. It might just be a coincidence, but it seems to happen more readily with coffee that I brew over ice. I press my areopress directly over ice, I've heard this reduces the acidity. Which would make sense, as acidity usually wards off mold. I leave all of my coffee black and unsweetened, so it is not dairy or added sugars that are causing this.

Perhaps try variating your brewing process. I'd be especially keen on the pH. Maybe there are some spores which will not grow in environments below a certain pH.

> **Comments:**
> **username_0**: Low molecular-weight sugars in coffee are almost totally degraded by roasting (see Redgwell and Fischer, *Coffee Carbohydrates,* Brazilian J. of Plant Phys., 165-174, 2006 at 172). Also I think that the variation of acidity in brewed coffee doesn't deter molds any more than it deters people. You *could* change the pH but I am mainly interested in molds that grow in coffee that humans would find drinkable, and whether ones other than those I mentioned ever appear. As for the time to appear--I think you are right, about a week in warm weather.  

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### Answer by username_3 on 2018-01-06. Score: 0

I am severely allergic to Penecillium Mold. Around a year and a half ago, I began drinking coffee on a daily basis. I had my french press brewing set up perfectly to have a nice mug every day. After about 6 weeks, I had an allergic reaction. Mold spores cause a reaction in allergic people whether they're alive or dead, so the previous answerer is wrong about being dismissive about the mold being killed in the roasting process.


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