I have stout fermenting and it has been in my carboy for a little over a week. Yesterday I opened the carboy to make a small intial addition of coffee beans and cacao nibs. Well when I opened it and smelled the brew, I got a strange almost plastic or rubber smell coming up from it.

Is this due to how young it is?

Should I worry about it?

I did everything down to the last detail so I cannot imagine it is contaminated. I hope the smell goes away.

  • Did you filter your brewing water? What did you use to sanitise? Commented Jul 20, 2015 at 14:18
  • So... how did it turn out?
    – Kingsley
    Commented Feb 26, 2018 at 23:46

3 Answers 3


At the 1 week stage: do not worry.

If it's still there in a few weeks, sure, worry then.

All sorts of weird flavours come off yeast when it's actively fermenting. For example lager yeasts can just smell plain rotten (eggs, sulphur, ick!), but afterwards you get beautiful clean beer.

Forget about it for a week (or even 2), and start planning your next beer to keep your mind occupied!


What kind of water do you brew with? Chlorinated tap water can cause a rubber-like (Chlorophenol) taste or smell. If you pass tap water through a chlorine-removing filter, it might be time for a filter change.

  • You can also remove chlorine and chloramine by adding a Campden tablet to the brewing water. Commented Jul 19, 2015 at 15:25
  • used bottled spring water.I was using a standard off-white rubber stopper and noticed strong odor from it. the smell was nearly identical to what i was picking up in the beer. changed it to a pure white stopper with no smell, and since have noticed the smell come down a bit. I also added 1 oz coffee bean, 1 oz cacao nibs, and 1 whole vanilla bean. still very young so i think it should balance out. I plan on adding the remaining 3 oz coffee beans, 2 oz cacao nibs, and another whole vanilla bean a week before kegging to really accentuate those toasty coffee chocolatey flavors from my grains. Commented Jul 20, 2015 at 16:38

I would worry about that smell. Several of my local home brewers have made plastic flavored beer, it doesn't go away, just gets stronger. When it happened to me, the beer went away, and the fermenter too.

  • It has happened to me a few times too, It can be chlorine, or contamination, it doesn't go away, and usually have to toss the whole batch.......if it is from contamination, I would double check your equipment and try to find the source. or review your process. for me the 2 times, it was from the bottling spigot, and re-pitched yeast.
    – jsolarski
    Commented Oct 24, 2017 at 13:51

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