carbonation/temperature question

[jungdahl]

I kegged some root beer at 37 degrees 25psi and it was good. I'd get a good pour, good head and tiny bubbles coming off the glass. I noticed the thermostat had been turned down and the temp was about 34. I turned the thermostat back where it was but I get a different pour.
Sides of the glass covered with bubbles but larger ones 1/16 - 1/8. The root beer became flat before I finished the glass.
Is this to be expected with a temp change?

 

[day_trippr]

According to our favorite carbonation table, if allowed to reach equilibrium, the combination of 37°F and 25 psi would result in 3.84 volumes of CO2. From what I can gather, anywhere from 3.6 to 4 volumes is right for root beer.

Dropping the temperature to 34°F would eventually result in 4.10 volumes of CO2, which is on the high-side, but barely so. It would take some time to get there though - definitely more than a couple of days - and I'd be surprised if the pour would be visibly different, but I've been surprised before

Two questions:

- when you poured your last glass was there much more foam ("head") in the glass than before? If so, that would explain why the root beer goes flat earlier than before: much of the carbonation was lost during the pour.

- how long is your root beer line and what inside diameter is it? Just like dispensing beer, root beer needs the dispensing system to be balanced between pressure and line resistance to provide a suitable pour. Short lines can be problematic in that regard. Your line might be on the hairy edge such that a little more carbonation pushed it over to where there's lots of CO2 breakout...

Cheers!

 

[Tobor_8thMan]

Don't forget about the root beer in the tubing as it will lose some CO2 depending on how long it sits.

 

[camonick]

Sides of the glass covered with bubbles but larger ones 1/16 - 1/8.

I’m not sure if root beer behaves the same as regular beer, but what you described here can be signs of a “dirty” glass. It might appear clean, but there is a film or something on the inside of the glass creating nucleation sites. This can cause a lot of CO2 to come out of solution faster leading to a flat drink.