What type of infection am I dealing with?

[Supry]

Brewed a tart cherry stout, lots of acid malt, frozen, then thawed cherrys added at 5 min left on the boil. OG 1.068 (was supposed to be 1.078) after 1 week gravity was 1.040, may have seen the start of this infection at that time but disregarded it. Stirred the yeast in an attempt to give it a kick in the butt after 1.5 weeks. 2 weeks in gravity didn't move but saw this when I opened the fermenter. It was a thin film that floated on top. Kegged it anyways, tasted fine. Ferm temp was unknown due to a broken thermometer on the fermenter, but should have been between 65-75.

https://imgur.com/a/Zfdoco4

 

[Rob2010SS]

Brewed a tart cherry stout, lots of acid malt, frozen, then thawed cherrys added at 5 min left on the boil. OG 1.068 (was supposed to be 1.078) after 1 week gravity was 1.040, may have seen the start of this infection at that time but disregarded it. Stirred the yeast in an attempt to give it a kick in the butt after 1.5 weeks. 2 weeks in gravity didn't move but saw this when I opened the fermenter. It was a thin film that floated on top. Kegged it anyways, tasted fine. Ferm temp was unknown due to a broken thermometer on the fermenter, but should have been between 65-75.

https://imgur.com/a/Zfdoco4

I would agree that's an infection but no idea what it is. Is that the start of a pellicle? It kind of looks like it where you can see "bubbles" forming under the top layer.

Acid malt in a stout? Usually stout grain bills are too acidic and need the addition of baking soda to keep the mash ph in check. Do you check mash ph?

So your FG was 1.040? That's where it stopped? I suspect your infection might have come from stirring the yeast, assuming you used something to stick in the fermenter and stir around.

 

[Gnomebrewer]

I also agree that it's an infection, but don't know what it is. My only comment is that (if you use your imagination) it looks like a poodle.

 

[Supry]

I would agree that's an infection but no idea what it is. Is that the start of a pellicle? It kind of looks like it where you can see "bubbles" forming under the top layer.

Acid malt in a stout? Usually stout grain bills are too acidic and need the addition of baking soda to keep the mash ph in check. Do you check mash ph?

So your FG was 1.040? That's where it stopped? I suspect your infection might have come from stirring the yeast, assuming you used something to stick in the fermenter and stir around.

I was experimenting with adding the acid to simulate a sour stout. The fermentation stopped before I stirred it to try to get it to finish, obviously it didn't work. Ph at the time of kegging was about 4.6 when I used a test strip.

 

[RPh_Guy]

Usually stout grain bills are too acidic and need the addition of baking soda to keep the mash ph in check. Do you check mash ph?

I think Rob may be on to something. Your mash pH might possibly have affected your wort's fermentability.
Test strips are unreliable.

That is clearly a pellicle forming, which indicates the presence of wild yeast and/or bacteria.

Since it tastes fine, nothing to worry about. Clean your equipment well after use.

 

[Jackanapes]

What type of infection it is, is hard to diagnose by looking at it, but good rule of thumb I've learned is if it doesn't get fuzzy and black or blue, you might have dodge the mold bullet. Either drink it fast and soon, or let it ride and see what you get.

Since it tastes fine, nothing to worry about. Clean your equipment well after use.

Iodaphor or a bleach solution (1 tbl/ 1 gal water) will kill most things. Just be careful and more diligent with plastics as those are much harder to sterilize than stainless or glass.

 

[RPh_Guy]

Surfaces need to be clean before they can be sanitized.
A soak in an alkaline cleaner like PBW is recommended between brews to remove residue and biofilm. Some residue like "beerstone" can be extremely difficult to remove if it gets to the point where it's visible.

Before use, any no-rinse sanitizer is fine. I use Star San.

 

[Supry]

Yah, we usually soak the fermenter in bbrite and wash them when we are done with them, then a spray with star san just before transferring into them. Not sure what I missed this time, could have been the cherries also. We tossed the fermenter since it was getting old, stained and scratched. I feel better now that everyone is pretty sure it isn't mold and safe to drink. Ive been brewing for 10 years, maybe 100 batches, and this is my first infection.

 

[Vale71]

The source of the infection is most likely the cherries. Fruit is a receptacle of all sorts of nasties and 5 minutes boil is really cutting it close.
From the pellicle it is clearly something strictly aerobic, a good bet would be pichia membranifaciens which will mostly metabolize alcohol but with hardly any foul-tasting by-products. When you get such an infection the beer tastes fine initially but as the infection progresses it tastes thinner and thinner because of the dwindling alcohol content.
Of course this is just a guess, without making a culture and placing it under the microscope a guess is (almost) as good any.

 

[RPh_Guy]

Pichia metabolizes alcohol? Is it just that species?
Some Pichia strains can be used for primary fermentation. Don't know the species off the top of my head.

 

[Vale71]

Yep, much like acetobacter they can (aerobically) metabolize ethyl alcool reducing it to water and CO2. Unlike acetobacter they don't produce a vinegary note but rather a solventy one (ethyl acetate).
Much like acetobacter it can ferment simple sugars, so it can be used for primary. Since finished beer lacks simple sugars it will have to feast on alcohol alone, once again just like acetobacter.

 

[Supry]

Thanks again. Since it can aerobically metabolize ethyl alcohol, does being in the keg under co2 pressure and cold keep it from further causing an issue?

 

[RPh_Guy]

I don't think it's good to make guesses about what organism(s) are involved when someone posts a photo of a pellicle.
1 & 2. There's not necessarily only one contaminating microorganism and there's no proven reliable way to know what it is just by looking at the pellicle. It's like trying to determine the variety of a hop by looking at a photo of a handful of different varieties of hops. That sounds crazy, right?
3. Even microbiologists with experience growing various microbes on agar plates don't necessarily know how it would appear on liquid wort/beer since it's an entirely different growth medium and a polymicrobial culture.
4. New species and strains are being created and discovered all the time, besides the myriad that are already known. There are simply way more microbes than a single person could have studied and the different/new strains may all have different characteristics. To my knowledge there is not a complete list anywhere of microbes that can form a pellicle. There aren't any published guides to even approximate identifications by looking at a pellicle. Pellicle formation simply isn't an active area of scientific study.
5. Even under a microscope it's easy to make mistakes. Microbe genera/species are reclassified or mistaken all the time. Just look at WLP644 as an example in brewing. There's seems to be continuous debate and revisions for restructuring various levels of taxonomy and reclassifying microbes.
6. As soon as you mention a specific microbe, people start worrying about that only that one, ignoring other possibilities. I don't see how making guesses is beneficial to someone looking for help. The only potential problems with contamination are off-flavors/aroma or superattenuation, which are relatively simple to detect, monitor and prevent. Superattenuating wild yeast contamination seems to be very rare.
I suppose it's our nature to want to know and try to figure out what it is, but there's simply no way at a macro level.
Just my opinion. Am I missing something?

EDIT: I should mention that the above is in reference to pellicles. Mold does look different (vs. a pellicle), and is potentially dangerous.

@Supry
If there are no obvious flaws and gravity is stable, just treat it like any other beer but continue to monitor it

If you really want to know, send a sample to a micro lab that can run genetic tests.

@Vale71 thanks. I think I did read that before about Pichia. I'll try to remember it this time!
Can you help me understand how you know the thing forming this pellicle is "clearly something strictly aerobic"?
Thanks

 

[Vale71]

Strictly aerobic (don't know if it's the proper English term as I studied the subject in German) means they can only be active in the presence of oxygen. Such types of bacteria when inoculated in a basically oxygen-free environment will have to gather at the surface, where there is a sufficient level of oxygen to sustain their metabolism, and this is actually the reason why they form a pellicle but the beer underneath appears unaffected as it is actually free of infection. That's also the reason why they are the slowest-acting of beer spoliage bacteria.
Strictly anaerobic bacteria (such as some strains of lacto) will on the other hand actually stay away from the surface where they would be poisoned by oxygen and hence tend to gather at the bottom of any vessel, thus forming a visible sediment if given enough time.
Bacteria that are either aerobic or anaerobic may form a pellicle but the beer underneath will also show signs of infection, such as excessive turbidity or excessive sedimentation. It will also generally tend to spoil at the highest rate.

As far as identifying them without genetic testing, it is actually possible in the case of beer as it is a selective environment which will allow only a limited number of species to thrive. All you need is some selective growth media, a microscope, hydrogen peroxyde and some test strips and you can indentify them with 99,9% certainty. This was actually part of my training and loads of fun to practice too!

 

[RPh_Guy]

That all makes sense. (In English the proper term is obligate aerobe / obligately aerobic but I knew what you meant)

Bacteria that are either aerobic or anaerobic may form a pellicle but the beer underneath will also show signs of infection, such as excessive turbidity or excessive sedimentation. It will also generally tend to spoil at the highest rate.

This is why I was questioning the assertion that it's clearly an obligate aerobe in this case.
It's difficult to determine the turbidity of a stout, certainly with Saccharomyces contributing. There will be plenty of sedimentation because it's beer, and there's lots of yeast and trub.
Off-flavors may be still below detection threshold, or may be masked by the other strong flavors in the beer. ?

 

[Vale71]

That was more an assumption on my part as the OP did not report any other obvious symptoms. Sediment from yeast is easily distinguishable from that attributable to an infection as bacteria do not tend to flocculate and will leave a very loose sediment that will tend to be roused with the slightest motion.
But of course, as I already said this is just a guess based on a description off the Internet, to be sure I would definitely need to obtain a sample.
BTW, in German it's "obligat aerob". Not much difference there, except for pronunciation of course...

 

[Vale71]

Thanks again. Since it can aerobically metabolize ethyl alcohol, does being in the keg under co2 pressure and cold keep it from further causing an issue?

If and only if I guessed right than yes, minimizing oxygen availability will slow down the infection and you might still be able to enjoy your beer. I would still suggest throwing a party and quaffing it all as soon as possible with the help of your friends and family.