Suspected infection

I think I may have an infection issue but want to get some more opionions. I brewed a bourbon oaked porter back in January. The beer finished up at 1.017 FG (target according to my BeerSmith recipe was 1.018). I used Wyeast London Ale #1968 yeast, no starter due to small batch size. Left the beer in primary for 3 weeks then secondary for 2 weeks - added bourbon soaked oak chips the final week. The beer was great for at least a month after it finished carbing. However I just cracked one open this weekend and got a gusher. Opened 3 more bottles with the same result - damn!

I checked the gravity on one of the opened bottles (after letting it de-gas) and it was 1.012. So obviously the beer came down another 5 points in the bottle! I am leaning towards an infection vs. bottling too early because the gravity is lower than the target. Other than being too dry, the beer tastes fine - no off flavors or funkiness. I have never really tasted infected beer so I don't know if it would have off flavors. Also, I only used 1.8 oz. of sugar in 3 gallons at bottling (shooting for 2.0 volumes CO2) so I don't think I added too much.

Any thoughts?

Hard to say. May just be regular attenuation that got jump-started by the priming sugar, or it could be a gusher infection. What does the head of the beer look like? Gushers will often produce an unusually coarse head that doesn't look like the dense heads a regular beer produces.

ArcaneXor said:

Hard to say. May just be regular attenuation that got jump-started by the priming sugar, or it could be a gusher infection. What does the head of the beer look like? Gushers will often produce an unusually coarse head that doesn't look like the dense heads a regular produces.

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I poured it into a glass and the head is fairly even across (i.e. not rocky looking) but the bubbles larger than normal. Once the initial foaming stops it settles into a pretty normal looking head although the head stays for a long time - not like a typical porter where it would be gone after a few minutes. Could this have "normally" fermented down to 1.012 even though Beersmith says it should have finished at 1.018?

Yeah, that can happen. Factors like mash temperature, yeast pitching rate, fermentation temperature profile, etc. can result in higher-than-expected attenuation. I usually finish about 3-4 points below than what Beersmith expects.

So are you thinking that the lack of a rocky, uneven head points more towards over attenuation vs. infection? That would be easier to fix as opposed to chasing down the source of an infection.

I'm just a noob...but logic would dictate that since your FG is still dropping, you don't have an infection, you've still got active yeast cells. Bacteria would consume the sugars, but wouldn't cause the FG to drop, because they don't produce alcohol as a by product. Also...if you had an infection...you'd be able to see rings around your bottles and a funky taste or smell...since you described neither...I think you're beer is just fine.

If I'm wrong...other folks feel free to correct me (again, I'm just a noob)

Edit: I suppose one thing it could *possibly* be is a wild yeast infection.

jdlev said:

I'm just a noob...but logic would dictate that since your FG is still dropping, you don't have an infection, you've still got active yeast cells. Bacteria would consume the sugars, but wouldn't cause the FG to drop, because they don't produce alcohol as a by product. Also...if you had an infection...you'd be able to see rings around your bottles and a funky taste or smell...since you described neither...I think you're beer is just fine.

If I'm wrong...other folks feel free to correct me (again, I'm just a noob)

Edit: I suppose one thing it could *possibly* be is a wild yeast infection.

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Thanks for the information about bacterial infections - that's good to know.
Would wild yeast impart any funky flavors? I know there are many Belgian styles which are made with wild yeast and those have a distinct flavor, but I'm not sure if there are other types which are flavorless?