Infected Batches...

[Evan!]

I have a few batches that changed, night and day, between carboy and bottle, and my friend (who got me started brewing) thinks it might be infection.

The major two candidates are an oatmeal stout and a london ale. While they were in carboy, they tasted great. But after bottling, they both exhibited very similar flaws: overcarbonation and sourness. My friend thinks it's a bacterial infection---because the bacteria eat sugars that the yeast can't, and produce the extra carbonation, and the byproduct is the sourness.

Anyone know anything about this?

 

[zoebisch01]

Sourness is often a result of lactobacillus or acetobacter infection. Lactobacillus strains that are tolerant of hops are much less common than those that are not though. This might not be a bad thing (maybe you can find a creative way to use it). Overcarbonation is usually a sign of wild yeast, and gushers from the bottle are usually what happens. They have the ability to pretty much consume all or most of the sugars from what I understand. I guess I should point out the two symptoms could point to different things. I am not certain if the gushers exhibit sourness.

 

[cweston]

Is it every single bottle, or just some bottles?

If only some bottles, then I'd say it is definitely a bottle-related infection issue.

 

[Evan!]

No, it's every bottle, without fail.

 

[zoebisch01]

No, it's every bottle, without fail.

The batch probably caught a bug. Make sure you aren't kicking up grind dust in your near your fermentors. The grain is full of lactobacillus and can carry wild yeast. Oh plus, your brew area may be harboring them...so a thorough vacuuming and sweeping might be in order. Also look for possible sources for airborne carriers (fans, registers etc)