Recirculated dry-hop, air bubbles in hose at pump outlet

[HopSteady]

We are testing a new dry hopping technique on small batch sizes which involves recirculating with a pump from the racking arm and pumping up into the bottom of the cone (see image).

The pump (Flojet NDP 35/3) is run for a few minutes 4 times per day to rouse the hops. As it is running, and for some time after, I notice considerable airlock activity. There are also tiny bubbles visible at the pump outlet in the hose travelling upwards into the bottom of the cone.

The pump housing and beer lines are of course properly sanitised and flushed of air before connected to the fermentor.

The concern of course is whether this is oxygen ingress. Perhaps it is dissolved CO2 getting stirred out of the solutions, I do not have a DO meter to confirm.

After 3 days of running I tasted a sample and it tasted extremely fresh, no oxygenation to be detected. The pump also seems to be very well sealed with a rubber ring under a good amount of sealing pressure.

I am trying to understand the science behind the formation of these air bubbles:

- Is this likely dissolved co2 rather than oxygen ingress, would this make sense?
- If I am in fact pumping in o2, how long would it take for the beer to oxidize?

Thanks a lot for any help on this.

[jebzter]

Your suction side is seeing lower pressures, probably CO2 escaping.

[Junkyard]

yeah I would venture to guess it is dissolved Co2 coming out of solution. Even room temperature, atmospheric pressure beer that has recently fermented will still have a small amount of dissolved co2, when your pump is stirring it up it will come out of solution.

We tried this same recirculation idea for our DIPA a couple times, we tested the results back to back with a batch that was normally dry hopped and we felt like the normally dry hopped version was better and had a brighter hop character.

i'd be very interested to hear your end results

[krichard]

More than likely CO2 coming out of solution. Check all of your seals and make sure they are air tight. We continuously recirculate our dry hops for 24-36hrs and have had significantly better results over traditional dry hopping techniques. I'd suggest just leaving the pump running instead of starting and stopping it.

Check out this research study for reference: http://ir.library.oregonstate.edu/xm...pdf?sequence=1