Looks like Euglena to me. They are common protists found in water. They are photosynthetic (why they appear green in most pictures and diagrams) but ethanol will draw the chlorophyll from the choloplasts.
That solves the mystey. Thanks. The things did indeed look like this image from the web:
Not sure yet where exactly it was hiding since I doubt that they can live in beer.
what water are you using to dilute your sample? You will need sterile filtered water if you don't want to see contamination such as this.