Did wild yeast take over my starter?

[HerbieHowells]

A little over a week ago, I bought a bottle of Fuller’s 1845, mostly to play around with harvesting yeast. I decanted all but a little bit of the beer, made up about 8 ounces of wort, cooled the wort, and pitched into the bottle using a sanitized funnel. I then placed a piece of sanitized foil over the top of the bottle and let it go. I got a nice yeast deposit at the bottom after about 36 hours. I (perhaps foolishly) let it sit for a week at 68 degrees, still covered with the foil.

This weekend, I had some time to burn, so I decided to brew a half gallon of bitter to pitch that yeast into, hoping to end up with a few beers and enough yeast to wash and save for a future starter. When I lifted the foil off of the bottle, I noticed that it had a strong sour odor, somewhat reminiscent of a Belgian beer. It was strong enough that I decided it was not worth continuing the experiment. (I happened to be bottling, so I ended up pitching some yeast from the mild cake I had on hand, so at least I will still get a few bottles of bitter).

Does that sound like wild yeast took over my bottle, or did I overreact?

 

[theredben]

Could be anything, but would likely be Acetobacter bacteria (the ones that make vinegar). They are extremely common and need oxygen to reproduce. That is why we need airlocks on fermented beverages (beer/wine/mead...), is you keep out the oxygen, you keep the vinegar away!