Originally Posted by togodoug
It seems most people think its sanitation. I don't like that idea because I think I'm doing all I can, including changing siphon tubes and fermentation bucket. This brings me to two questions:
1. If its yeast v. bacteria, can someone describe the difference in taste? What does infection taste like and what does bad yeast taste like?
2. Has anyone thought of oxidation? I have noticed some air bubbles in my siphon tube, it can come in where the tube attaches to the auto siphon. I have also sloshed the wort a lot, poured it to transfer bucket while still about 100 degrees and put it in an ice bath and spun it (like a champaigne bottle in an ice chill at a restaurant I can't afford). I wonder if this could be the issue? I've used this method of chilling a few times, some of them came out fine so I doubt it. The air in the siphon hose I wonder about. What would oxidation taste like?
In light-colored beers the off-flavors produced by oxidation are often described as paper, cardboard or lipstick. In darker beers the maltiness tends to fade and you will get a sherry-like flavor, which some people actually find quite pleasant (including myself in a dubbel!). Oxidation can also cause bread-like or butter-like flavors.
A good way to familiarize yourself with the flavors caused by oxidation is to get a 12 pack of good domestic beer, put half of them in the fridge and half in a hot place. After about 1 week of being in a hot place, take one out and put it in the fridge for 24 hours. Then, taste it side-by-side with one that has been refrigerated the whole time. Repeat the process every week and you will notice a difference in the flavor of the cold-stored beers and the hot-stored beers (this is why I almost want to SCREAM when I see people buying craft beer at a store where it is not refrigerated).
As far as an infection goes, the off-flavors can vary widely. I only had one batch that I'm sure was infected because it continued to ferment in the bottles after having reached FG and fully carbing. Upon opening, the beer gushed out like a fountain and the taste was sour.