Like, don’t have guests over to your house reek. Like, neighbors think you have an overweight Green Bay Packers fan sitting in your basement eating sauerkraut 12 hours-a-day reek.
You get the idea.
There are three questions that homebrew shop owners regularly get about the odiferous output:
- Why? (Extension: Why not all the time?)
- Is it bad?
- What can I do about it?
1. There are lots of articles out there to whip you up into a full-on panic attack about the smell. John Palmer’s website, for example, throws out the dreaded term “Bacterial Infection,” mentions that it might be your yeast strain, but BACTERIAL INFECTION! AAAAAAH!
OK, if you are making mead, cider, white wine, lager beer, or Belgian beer, it’s almost certainly Hydrogen Sulfide being produced by your yeast. It is perfectly normal for some yeast strains. It is not a reason to panic. Hydrogen Sulfide, H2S, is a natural secondary metabolite of many yeast strains, especially ones which ferment in low mineral content environments, like cider and mead yeast. (You can learn more about secondary metabolites here.)
If you are making one of the above beverages, and it smells like cheese farts, don’t worry! It will go away with time. Your mead will not continue to smell like the south end of a cabbage patch.
2. However, other yeast strains, such as ale strains, do not, as a rule, put out H2S. If you’re making an IPA, and it smells like rotten eggs, that’s probably not a good thing.
Other smells, such as vinegar, green apples, or bile are bad, pretty much always.
3. What can you do? Don’t have people over for a week. Or, ferment warmer and risk ruining your beverage. Or, have a really big house where you can ferment far away from friends and relations.
Or, do what we do: Get a huge-ass carbon-filter air purifier.