Carbonation/Stratification Issues with Separator Transfers

[MN_Nice]

Hey everyone, have a BBT carbonation issue that's confounding us here at the brewery. A little background: we generally use 60bbl FVs and 60bbl BBTs to process our beer for packaging. There's a couple 30bbl of each as well but most batches are in the 60s. In the past during transfers we used a custom built piece of equipment that would pump in our finings in line to the block and bleed over the course of the transfer, then once the beer was filled in the BBT we'd apply head pressure to 15psi and then carb through our carb stones. No issues getting consistent carbonation levels within a pretty consistent timeframe.

A few weeks ago we upgraded our brewhouse with a separator, and we no longer use the in-line finings machine. The separator takes longer to fill the BBT, so we decided to start carbonating as soon as the beer level rises above the carb stone. We now get the FV and BBT both up to 15PSI before starting the transfer and then run an umbilical between the two to maintain that level of head pressure throughout the 2-3 hour transfer. Once the beer level rises above the carb stone we apply CO2 through the stone, check the carb level at the end of the transfer, and then continue carbonating normally afterwards.

Here's the problem: the CO2 level seems to jump up a full .10 - .15 overnight from the point we stop carbonating. So for example if we finish a beer at 2.60 we'll come in the next day and it's at 2.70 - 2.75. This has been a consistent issue with every batch we've run through the separator so far...and it doesn't seem to matter if the beer is in a 60bbl tank or a 30bbl tank. This was never an issue with pre-separator batches.

To add a wrinkle into the equation, last night I transferred a batch that was at 1.90 in the BBT at the conclusion of the transfer, up to 2.80 after only 90 mins of carbonating afterwards (WAY faster climb than normal) and then read 2.24 when we came in this morning. I triple checked the 2.80 reading last night because it was so out of the ordinary.

Any ideas about what might be going on here? I've read a little about CO2 levels stratifying but I'm not sure how that could be the issue or what switching over to a separator might have had to do with it.

Any thoughts are much appreciated. Cheers!

[PruBrew]

Stir BBTs

We have definitely experienced similar issues on tanks ranging in size from 40 to 100 bbl. We have had some success stirring the tanks to help homogenize the carbonation levels. We will normally stir using a trickle of CO2 going into the bottom of the tank while carbonating through the stone, then stir the tank vigorously with 2-3 short, big bursts through the bottom before taking a reading.
If there is not enough movement introduced to the tank either from the transfer or the carbstone then the initial beer in the tank will have CO2 moving through it during the entire carbonation process (as the bubble move up to the surface) while the last beer into the tank will never have CO2 actually flow through it unless your carbstone in in the bottom of your tank. It seems generally true that there is more CO2 in solution near the top of the tank, near the gas/liquid interface, though results from before and after stirring don't always support this theory.
The CO2 in solution from carbonating will equalize throughout the tank given enough time, as you are observing with your morning-after readings. It does seem however that residency time in the tank can affect distribution of CO2 in solution via temperature, hydrostatic pressure and absorption from head space.
Cheers.

[MN_Nice]

Great reply Walker, thank you very much for that insight. I passed your ideas to the rest of our team and we're going to give them a try.

Cheers!