Can a beer go sour overnight?

[Horseflesh]

A couple of weeks ago I brewed a pale ale. I kegged it last night, and the sample from the fermenter tasted GREAT. Today, about 24 hours later, I tasted it from the tap. It is still undercarbed, but it tastes like a different beer. It's kind of sour. Even when it warms up, it's still a little sour. I tried dispensing through some different lines, but there was no difference.

I checked the pH of the pale ale and it is 3.7, which seems low. I tested my other 2 beers on tap and they were 4.1 (hefeweizen) and 4.0 (mango wheat).

I added a TINY bit of baking soda to a pale ale sample, and the sourness dissipated. It hit pH 4.5 and tasted much better other than the gross mineral note from too much sodium.

So: If I got something like a lacto infection when kegging, could it sour a keg overnight?

More data:

- Mash was pH adjusted and I added minerals, but all the pH values checked out. (mash pH 5.44)

- Fermenter is stainless

- Beer was dry hopped 7 days before kegging (I just dumped 3 oz of pellets into the fermenter.)

- Samples tasted great throughout fermentation and on kegging night

- I kegged by purging a Star San filled keg with CO2, then used a line from the fermenter valve to the OUT post on the keg. Keg gas purge valve was locked open to release CO2 as the keg filled.

I can't think of any sanitation mishaps but the fermenter valve or the transfer tubing/liquid post could have been poorly sanitized. Other than that I am out of ideas, and if y'all tell me that a beer can't sour overnight then I am really stumped. I guess I could have gotten an infection when dry hopping but it would be strange for it to really kick in on day 8.

 

[k47k]

It's possible for lactose to sour overnight but you'd need a lot of it at a warm temp and ibus inhibits lacto so I'd say it's unlikely.

 

[JonM]

You might have gotten a mouthfull of yeast last time, your palate might have been messed up from spicy or fatty food or from eating something sweet, etc. I wouldn't jump right to infection. I bet it's something far more innocuous.

 

[Horseflesh]

Something definitely changed. After sitting for a couple more days, and blowing out some more cloudiness as the keg cooled, the beer tastes normal. pH even increased! I'm going to start a thread about that in Brew Science.

 

[maierhof]

This is the exact problem I had. It took me a very very long time to hunt it down. You said it - it is probably either your hoses, quick disconnects (think behind the washer), or even you dip tube to the keg (more washers)..

Really don't understand how it went away though - if that is the case my money is on the keg dip tube not being entirely clean but given your above comments it sounds as if you got an acetobacter bug somewhere in there. Time to take the keg ball lock (if corny) apart for a deep clean... if sanke maybe do an acid wash w #5.

Of course I could be wrong though - it took me ruining 7 batches before I finally caught mine... doh!

Edit: the bug was probably already spreading as you tasted it but it was under your taste threshold at that point. Jon has a point too... soo many variables