I recently encountered by first contaminated brew. It looks like it was some sort of wild yeast contamination. I am not quite sure how it happened – I am very careful about sanitising everything.
There have been a number of successfully brews since, so it can’t be something that I am doing routinely or an equipment issue. Otherwise, the subsequent brews would also have been contaminated too. Hopefully, it is just a one-off.
However, it did get me wondering about where in the process the problem occurred and what I can do to eradicate these problems in the future.
Possible causes
- It couldn’t have happened before the boil was finished. The temperatures here would have killed off any wild yeast;
- The heat exchanger is run at >90C for the first 10 minutes, so it is unlikely that this is the issue. This would kill off any wild yeast;
- There could have been an issue in the transfer from the Grainfather into the fermenter once the wort had cooled down. But again unlikely as the transfer tube from the heat exchanger was run at >90C before transferring to the fermenter;
- The wild yeast could have been in the fermenter itself before it was filled. Maybe it hadn’t been properly sanitised;
- The hydrometer or thermometer that I used in the fermenter could have been contaminated. Again maybe either were not properly sanitised;
- Something could have got into the fermenter during fermentation. It seems unlikely, but it could be possible;
- The FG was 1.003 which is way too low and proves that the beer was already contaminated before bottling. So it isn’t anything to do with the racking or bottling process.
It then occurred to me that I am doing something stupid! Once the fermenter is full, I am putting the hydrometer (and a temperature probe) into the wort before pitching the yeast. Duh! The obvious thing to do here is to take a sample of the wort in a trial jar and test this for temperature and gravity. If the hydrometer or temperature probe is contaminated, it will only contaminate the contents of the trail jar and not the entire brew. This doesn’t really matter as the contents of the trial jar are thrown away once the measurements are made.
Even if this wasn’t the cause of my problem, this is an obvious improvement to my process.