Sour Smell

[Gazzala]

Opened the brew fridge this morning and was hit with a really strong sour smell coming from the dark ale + Lager Toucan brew - could this be a sign of infection? I lifted the lid to have a look inside and it looks the same as most earlier brews at this stage of fermentation (day 5).

I haven’t noticed this smell from any earlier brews. 

[Marty_G]

I have not experienced it but I believe from reading here that it is sulphur dioxide (SO2)  which is a by product of the fermentation process with some yeasts so is normal ...  however, I may be mistaken.  

[Beerlust]

Primary fermentation belches all sorts of off smells that can be construed many different ways by brewers.

Given what you've said though, sourness is often the sign of acidity. If your brew is infected it may be from a yeast source, or perhaps something like a lacto source. The lacto source will be easier to spot as it often manifests into a clotting on the surface (pellicles) with tentacle-like strands extending outward & downward into the wort/beer. Monitor the surface of the wort (try not to open the lid too much though) over the next few days for signs of this.

For the potential wild yeast side of things, if you haven't already, take a gravity reading & document it. take one in another two days time & then each day until the gravity is stable over 2-3 days. Let us know what that reading is once it's stable. Pour yourself a sample & taste it at this point too. Wild yeasts often ferment worts lower than a lot of standard yeast strains & impart off flavours & aromas with that. Your stable FG (if too low) could indicate a wild yeast has interfered with the ferment.

Don't worry too much at this point though. Just monitor the things I mentioned. Best of luck with the brew,

Lusty.

[Otto Von Blotto]

It wouldn't be S02,  that smells like rotten eggs. 

May or may not be an issue. I have smelt a little sourness at dry hopping time on ales before and they have been fine. As suggested just monitor it over the coming days.

[Gazzala]

Cheers fellas - will check and update when I get home from work.

[Gazzala]

Checked the brew tonight and the sour smell is not so bad now - took an SG sample and tasted it and it tastes great - probably the best tasting brew yet at the stage of fermentation. So I think it’s OK.