How fast can a beer's flvor change in the keg?

I've had 2 strange experiences with some beers I've brewed lately and I am at my wits end to figure out what has happened. Both times the beers had been kegged and were tasting very nice when suddenly the flavor changed.

The first was an IPA, basically a Two-Hearted-ish all Centennial. I breewd it, fermented 2 weeks, then into the keg. For the first 2-3 weeks, it tasted very good, nice hop aroma, little bit of malt, fairly balanced. Then after the third week, it started to get cloudy (it wan't the brightest beer because I had run out of whirlfloc) and after a week it had developed an odd flavor. A family member said it tasted "baconey" which is pretty close. I assume an infection, but given that it was in the keezer I was perplexed.

The second was a Saison. It was all galaxy fermented with 3711. Had a nice hoppy aroma from a 2 ounce dry-hop but was very dry and drinkable. Then over the course of a long weekend out of town, I came home and it had developed a strange sickly-sweet aroma and taste.

I've since dumped the IPA.

My other thing is between the time the Saison tasted good and went bad, I have cleaned my beer lines. 15 minute circulate of BLC solution, followed by clean water and then ran 1/2 gallon of star-san through.

Any thoughts on what might have happened to either of these beers?

 

no clue, but interested... subscribed.

 

Some of those off-flavors could be oxidation.

 

I've noticed my IPA's lose the resin sticky hop flavor pretty darn quickly when I keg. Like a week tops. Then the nose is still there but it's much more malty. It's annoying.

Not sure what would cause what you're describing though. Do you clean the dip tube and all the poppets after each beer? Did you take apart the faucets and clean them well? There can be some funky stuff that can accumulate in there after a couple beers run through it.

 

Hmm.. That's an interesting possibility. I hadn't considered oxidation being a slow process once the beer is kegged and purged.

 

In my opinion, oxidation is one of the more common flaws in homebrew. People think of it as a cardboard flavor but it actually appears as a wide array of flavors, from sherry, to paper, to lack of aroma, to an offputting sappy sweetness.

It can be tempting to write off the flavor as a mild infection or something. The fact that oxidation flavors don't appear until after the exposure (and can develop during cold storage) further complicates accurate detection.

I'm not saying its definitely what you're tasting but if you're confident you're not dealing with an infection, then looking at how the beer is handled post pitch and during transfer might be something to explore.

 

The time or two that I have had oxidation, the giveaway was the the beer color significantly darkened. Have you experienced any color changes with these two beers?

 

Sounds like oxidation to me.

When you presurize a keg to 14psi (at sea level) and release the gas, half the oxygen in the keg escapes. Assuming you have 2 liters of air in the keg after kegging and you didn't purge before hand, you have enough O2 to reach 150 ppm in the beer--way too high. You need to purge about 9 times to lower the O2 to 1 part per million, which is great from a beer that will be stored cold and consumed relatively quickly. You can use less CO2 by purging more at lower pressure.

Edit: I forgot to multiply by .2 in ppm above. You need 7, not 9, to reduced to around 1ppm O2.

 

It very well could be. I'm usually pretty careful about purging my kegs. Normally I fill then with starsan to the top and then push all the liquid out with CO2 but I know I didn't on these last 2 batches.

 

The "Star San Push" is also what I do to purge kegs before CO2-pushing the beer from carboy to keg.
Religiously - because otherwise a lotta work just went up in...air.

fwiw, I tend to agree with the prevailing opinion that you may well be tasting oxidation effects.
The whole wet cardboard/sherry character things are pretty much the terminal conditions.
I'd rank "strangely sweet" as more of a precursor...

Cheers!

 

Out of curiosity. Were the beers finished fermenting? To me it doesn't sound like oxidation.

 

It should be noted that the star san push does not remove any oxygen from the keg, it just replaces water with CO2. You need to purge before pushing to get the oxygen out of the tank before a closed transfer. If you open transfer, it's not really necessary to purge before, as long as you (and you must!) purge after.

 

What?

I fill a keg with Star San, then push it all back into a carboy using CO2.
It is the definition of a purged vessel...

Cheers!

 

Right, sorry. You have to fill it completely, i.e., no headspace, and then it's oxygen free. I push out the star san, but I don't do a closed transfer, so I leave some headspace.

 

Ok, I thought the universe had collapsed there for a second

fwiw, I fill the target keg until the Star San flows out of the PRV - the high point of the whole keg.
Between that and the post-fill flush, there can't be much if any "free air" left...

Cheers!