Harvesting commercial yeast - issue?

[slcdawg]

Let me start by saying I have made dozens of yeast starters and regularly wash and reuse yeast. I am very confident in my sanitation methods.

I am trying to harvest yeast from a bottle of Rogue Dead Guy. On Saturday I did a 1 cup starter in a sanitized spaghetti jar and was pleased to see the yeast multiply. Monday I went to step up to a larger 2 cup starter and noticed some white spots (.5mm diameter) near the top of the jar. My first thought was infection or mold but then common sense set in.

It smells good - like beer - no off smells. I am thinking there is no way it could be an infection or mold - has only been 48 hours. I did swirl the starter vigorously, and am assuming it has to be some dried beer/foam. However, I am having doubts - I hate to ruin a batch of beer over this. I normally do a starter in a 2L erlenmeyer with a stir bar - I've seen starter krausens but don't recall white dots like this in the past.

I did pitch the original starter into a larger erlenmeyer flask. I replaced the foil on the original jar and will keep an eye on it to see if anything grows.

Curious if anyone else has seen something like this? I took some pictures but none of them came out very clear. I will try to get a good pic posted tonight. If it smells good when I am brewing over the weekend, would you pitch it?

 

[ross_daly]

I'm trying to do something similar, and I have similar spots. What did you end up doing with it? I've definitely played fast and loose with sanitization on this starter, but I assumed that cell counts would 'win' over anything trying to get a foothold in the starter.

 

[EarlyAmateurZymurgist]

No commercially-produced bottle-conditioned beer is guaranteed to be 100% wild microflora free, which is why I always plate my bottle-conditioned beer crops for "singles" and grow my own pure culture. I also start the dregs from bottle-conditioned beers in 20 to 40mls of autoclaved (a.k.a. pressure cooked) 1.030 wort in an autoclaved container to ensure that I do not introduce any house microflora.

 

[ross_daly]

To close the loop, my impetus for posting was because I had tiny pinpoint white dots on the top of my starter wort. Those dots grew larger and eventually turned into... Kraeusen! I haven't brewed with it yet and I agree that it is probably not even close to 100% pure. The thing I was worried about was that it was 100% moldy and that seems to not be true. Following proper procedure and growing from a single sounds like the best way to go.