Where are the microbiologists?

[salty_dog_68]

Ii am new to yeast farming. I made slants and then inoculated them with white labs Cali ale yeast(wlp001). I made my first stepped starter cultures and stepped it up to a 1liter starter. I took a sample to do a cell count and noticed something besides the yeast. I did a gram stain and, sure enough, I can see a few bacterium mixed in with the yeast cells. Is it normal to have a little bit of yeast in the starter or did I infect It somewhere along the way (and need to recheck my sterile technique)?


The object of life is not to arrive at the grave intact and with a well preserved body...but rather to skid in sideways, beaten up and broken down, screaming, "holy ****! What a ride!"

 

[Hamaki]

I'm not a yeast rancher or microbiologist but I have isolated and propagated bacteria in a lab setting in the past with good success plating out monocultures. I believe that commercially available yeast products typically contain some bacteria at very low levels. I think your goal is pure cultures on the slants but more experienced hands may report whether this is achievable with yeast.

 

[WhamFish]

You should be able to get %100 pure yeast. How are you picking yeast to slant? I would suggest using a plate and selecting a single colony.

 

[Warthaug]

Microbiologist and yeast-rancher here. Bacterial contamination is not normal for yeast culturing. I maintain a large yeast bank, and my tolerances for non-mixed cultures is zero culturable bacteria. Generation times for bacteria are generally much shorter (20-60min) than yeast (2+ hours), meaning even a minor contamination can rapidly out-grow the yeast.

Since this is only WLP001 I'd recommend you throw it out and try again. Alternatively, if you're willing to try something a little more advanced, you could use streak-plating to purify the yeast from the bacteria.

On my blog I maintain a series of posts and videos on yeast ranching, starters, capturing wild-yeasts, etc. This includes a recent video "series" on making a home yeast lab that includes a video on streaking cultures:

• Yeast-ranching related posts/videos
• Wild-yeast related posts

I'll stop the shameless self-promotion now

Bryan

 

[BrewingChemist]

An antibiotic agar plate would eliminate the bacteria and enable you to purify the yeast out. That is what we do here in this household. Everything gets streaked on an antibiotic plate and brought up from there

 

[william_shakes_beer]

Interesting. I ranch without benefit of a lab setup. Is there anything I can add to my starter medium to reduce the bacterial colonies likely present in my samples?

 

[Warthaug]

If you have bacteria present in any significant numbers you would know it due to off flavours. Proper clean techniques & sanitization removes the need for anything "extra" to control bacteria. Using antimicrobials to cover up bad sterile techniques is not the route to go - especially given that its most likely to fail. Antibiotic resistant organisms are extremely common - adding antimicrobrials only ensures those are the ones which contaminate your wort...

Bryan

 

[william_shakes_beer]

Never had experience with off flavors, so I guess bacteria presence is negligable. Thanks.

 

[WoodlandBrew]

Agreed that you really shouldn't see any bacteria under the microscope. However, you could be introducing it just when you are making up the slide. I have used Methylene Blue that is made for fish tanks for staining which works fine for staining, but it also contains impurities. I use glass pipettes, but found the hard way that they are difficult to keep clean. Pulling alcohol through them is often not enough.