Yeast contamination in wyeast pediococcus 5733

[mnick12]

Hi everyone I encountered something interesting with wy5733 that has me stumped.

So two days ago I bought a package of wyeast 5733 pediococcus, and prepared one liter of the following medium:
Malt extract : 50g
Peptone: 5g
Yeast extract: 5g
Glucose: 10g

I found this on line as medium that is supposed to be suitable for the cultivation of pediococcus. Anyway I boiled and cooled the medium in a 1L flask with a stopper and stir bar.

Once the starter solution was cool I transfered the contents of the pack to the starter, sealed it with the same stopper and started stirring. I decided to take a look at drop of the 5733 left in the pack under the microscope. I added a drop of methylene blue and took a look from 40-1000x. I didnt see anything at all except chunks of organic material, nothing that looked like a bacteria or yeast.

Anyway I let the starter go and approximatly a day later I took out the stopper to give it a sniff (looking for diacetyl), and there was no smell. Anyway fast foward to the flask is visibly lighter and is producing CO2. I took a smell and it smells like fruit. Now pediococcus is supposed to be homofermentive so I put a drop under the scope, and it is loaded with small apiculate shaped yeast. I dont see anything that looks like bacteria just a bunch of lemon shaped yeast!

I am highly confused, how could a yeast get in there? I opened it once for less than 5 seconds, and this fermentation was evident in less that 24hrs after opening it.

Anyone experienced anything similair?

 

[kerosin]

Hi mnick12,
I observed some yeast as well and even isolated a/the contaminant yeast/s from a WY Pediococcus package using Sabouraud agar plates. Attached a micrograph of the isolate. I have no further information about this strain/s but sent it off a couple of months ago to a friend in the US for identification. Did not receive any results yet.

I however could observe the typical Pediococcus cells in the package (very tiny globular cells, often present in tetrads).

Cannot answer how the yeast got into the Pediococcus sample though. The yeast was very likely in the package before opening.

 

[mnick12]

Hi mnick12,
I observed some yeast as well and even isolated a/the contaminant yeast/s from a WY Pediococcus package using Sabouraud agar plates. Attached a micrograph of the isolate. I have no further information about this strain/s but sent it off a couple of months ago to a friend in the US for identification. Did not receive any results yet.

I however could observe the typical Pediococcus cells in the package (very tiny globular cells, often present in tetrads).

Cannot answer how the yeast got into the Pediococcus sample though. The yeast was very likely in the package before opening.

Hey!

Those are very similair to what I observed in my starter, I dont have a camera though.

I wonder what they are, and if they were added intentionaly? Please let me know what you find out!

 

[berebrando]

Maybe the yeast labs include yeast in their bacteria starters so that the cultures produce alcohol to reduce the risk of infection in the propagation stage. I don't know... Just a thought.

 

[mnick12]

Maybe the yeast labs include yeast in their bacteria starters so that the cultures produce alcohol to reduce the risk of infection in the propagation stage. I don't know... Just a thought.

Well that would make sense, pediococcus seems to thrive in already fermented beer. However when I buy a sample of pediococcus I want to buy pediococcus not a blend.

I am just glad I am not the only one to have observed this.

As an update I looked at another drop of the starter today. Fermentation has slowed and it now smells sulfurous. Under the scope I am seeing the same yeasts and a few small colonies of 10-20 round bacteria in a sort of blob.

Does anyone know where you can but PURE pediococcus?