Microbiology false positives - wild yeasts

[Cougue]

Hi everyone, I was wondering if you could share any advice or personnal experience concerning wild yeasts detection medium (LCSM, LWYM, SDA/LMDA). I am struggling a little bit with the results I get on our beers and I am beginning to think it may be related to false positive/reading errors while looking at the petri dishes.

Do you know if some yeasts would declare even though it's suppose not to, like saison or champagne yeast?

I also think S. cerevisiae declares but even looking at the Illustrated guide to microbes and sediments in wine, beer and juice, there is still some grey areas.

Thanks for your insight!

[AT-JeffT]

You could streak a bit of your culture yeast on a plate to find out. It's really the only way to know for sure.

Wild yeast media is tough to read and imperfect. BSI has a bit of info on reading LWYM Here.

[Cougue]

You could streak a bit of your culture yeast on a plate to find out. It's really the only way to know for sure.

Wild yeast media is tough to read and imperfect. BSI has a bit of info on reading LWYM Here.

We already did that with our regular yeast but not with those mentionned previously. With S-04, eveything was fine. Part of the struggle is while looking at the cells under the microscope, you kind of get lost. Some strains are pretty obvious while some others are hard to tell apart.

[wailingguitar]

That is interesting that you should bring it up. We had an outside lab testing for microbial contamination and were testing positive for wild yeast, that it had an odd cell morphology, and that it was the dominant strain of two yeast strains present. The beers did not present ANY indicators of wild yeast contamination; tasted right, no murkiness, etc. Yeast supplier sent a rep to the brewery, he watched me clean a tank, brew, etc and tasted all the beers. He was flummoxed since everything looked/tasted as he expected. He took samples and had them sent off for genetic testing and every sample came back as the yeast we were using with nothing else present. We have not yet found a conclusive answer as to why this was happening.