After a number of successful brews, I think I finally have a contaminated batch. I've always been good about sanitation (or so I thought) but I've steadily progressed from paranoid germophobe to a bit more relaxed.
I realize that it's not possible for anyone to definitively say what went wrong - but I'd still like to learn from this experience. As you'll see, this wasn't one of my better brew days! Wasn't a true disaster...but it was close.
My question: Of all the possible sources of contamination, are there any that stand out as more likely than others?
- Possible pellicle in the carboy, but nothing dramatic. Just a faint white skin over part of the surface.
- Carboy smelled okay (not foul) before bottling
- A sample tasted okay - not great, maybe a bit "thin" with less flavor than expected, but not obviously horrible
- REALLY BAD smell in the yeast cake after bottling. Much like that anaerobic bacteria smell from leftovers that are forgotten in a sealed container. The yeast cake also had more of a rubbery "mat" texture than a typical yeast sediment texture.
Here's how the brew process went. It didn't go quite like I wanted!
- First time with a partial-volume boil. Started with 2.5gal in a 6gal kettle.
- After the boil, added 3gal bottled distilled water to the kettle before transferring. (Metal didn't get hot enough to kill bugs on the sides of the kettle above the boiling wort, before adding water? Bugs in the distilled water or on the containers?)
- Siphoned warm wort to glass carboy (carboy and tubing were sanitized, but maybe not completely??)
- Wort did NOT get chilled like normal. I wasn't able to use my chiller, and assumed adding 3gal refrigerated water would be enough - but it only took it to about 100F.
- Figured this was too hot and would stress the yeast, so I loosely covered the mouth of the carboy with plastic wrap and ran some errands in town. (plastic wrap wasn't sanitized, but I figured it would be okay at the time)
- After about 3 hours, it had only cooled to 90F. I was getting nervous and pitched the yeast anyway.
- Pitched 2 packets of dry yeast - one came with a kit and I didn't know how viable it would be.
- In that 3 hours before pitching, the yeast was hydrating in pre-boiled water in a sanitized cup covered with a sanitized plate. But it still foamed over the edge and almost pushed the plate off! (still too exposed, maybe the foam-over picked up something from underneath the cup?)
- 2 WELL-hydrated yeast packs + 90F wort = MASSIVE yeast activity in just a few hours.
- In the morning, the wort had foamed up completely and fouled the airlock, which I replaced. (yes I sanitized the airlock & rubber stopper, but was a little lax about it, not expecting this to be as big a deal).
- Just overnight, the gravity was halfway to FG!
My best guess is that it went wrong in the 3 hours before pitching the yeast, when the wort was still very warm - and any bugs were then out-competed by the massive amount of yeast activity? All this yielding a not-horribly contaminated brew where most of the nastiness was buried in the yeast cake?
Between contamination and bad temp management, I don't expect this to be a good one to share, but ... had to happen sometime!