Fermentation Under Pressure & Dry Hopping

[Brew18]

Hi all,

Issue:
I just bought a conical fermenter in the last year and this is only my second time using it and fermenting under pressure. As part of my setup I am using the Spike PRV to pressure ferment, and as you can see in the picture, I have a butterfly valve on the hop addition side of the lid that has a sight glass with a pressure valve on top. For my previous batch, I completely purged the fermenter of all CO2 and then before adding the dryhops, I would purge the little chamber of any oxygen by cycling some CO2 through it.

Questions:
My question is, is it necessary to completely purge the conical of all CO2 before opening the butterfly valve? My pressure is currently at 11psi in the fermenter and aside from being worried that could cause the sight glass to shatter, I'm not exactly sure about the science behind any other issues. I imagine the pressure differential would just cause the hops in the sight-glass to get violently sucked into the fermenter, but aside from that (and potential shattering of the glass) are there any other adverse effects I should be worried about? I suppose I can always charge the dry hop chamber up to 11 psi to equalize pressure with the fermenter, but I'm just curious how others handle this process. I also wonder if purging all of the existing CO2 allows for the escape of all the aroma that I would have gained from the whirlpool at the end of the boil.

Lastly, does anyone feel that recirculation of the hops is necessary? The last batch I added like 4oz of dry hop and after 2-3 days or so, I noticed all the hops sank into the cone. I didn't feel like the beer had the aroma of 4oz worth of dry hops. I do a closed system transfer to my keg btw, so that is a non-issue. Thanks in advance for your input.

 

[McMullan]

The sight glass should be sufficiently rated to cope with FV pressures. You don’t really want to depressurise the FV. It’s likely to foam up even before adding the hops. Just purge air from the hop-loaded sight glass then equalise the pressure with the FV then dump the hops.

 

[Brew18]

The sight glass should be sufficiently rated to cope with FV pressures. You don’t really want to depressurise the FV. It’s likely to foam up even before adding the hops. Just purge air from the hop-loaded sight glass then equalise the pressure with the FV then dump the hops.

Thank you! So just purge the air out and then fill the chamber with 11psi (or whatever my FV is currently at)? Would you also recommend keeping the FV at pressure when I go to dump the yeast cake out after cold crashing? I have a 90 degree elbow I run off a butterfly valve at the bottom of the cone. I cap the end of that elbow off with a 1/2" barb nipple which I connect a tube to and place in a shallow bucket...so I'm not super worried about trub splatter going everywhere. Just not sure how safe it is to open a vessel that's under 15psi.

 

[McMullan]

You should have enough pressure to dump the yeast cone by then regardless. Obviously, open the valve gradually. No need for it to be fully open to push out the yeast in a controlled manner, rather than blowing a hole through the cone and wasting the pressure. Exploit it, with or without an external CO2 supply to maintain pressure.

 

[Franktalk]

The sight glass should be sufficiently rated to cope with FV pressures. You don’t really want to depressurise the FV. It’s likely to foam up even before adding the hops. Just purge air from the hop-loaded sight glass then equalise the pressure with the FV then dump the hops.

The PRV on my sight-glass hop dropper is only rated for about 2 psi. So I release the pressure from the headspace of fermenter, drop the hops and quickly add co2 to bring it back to the original fermenter pressure. I do it rather quickly, but I've never had an issue with foaming. I ferment at 15 psi.

 

[Brew18]

The PRV on my sight-glass hop dropper is only rated for about 2 psi. So I release the pressure from the headspace of fermenter, drop the hops and quickly add co2 to bring it back to the original fermenter pressure. I do it rather quickly, but I've never had an issue with foaming. I ferment at 15 psi.

That's good to know. I just did mine at 10 psi and equalized the pressure in the sight-glass chamber and there were no issues. Before I did this though, I realized I had to taken a manual reading from my hydrometer. Wanted to make sure I was close to the FG and for some reason the pressure seems to interfere with my tilt hydrometer so I take manual readings when pressure fermenting. It was nearly impossible to open the sample port at 15 psi so I just dropped it down to 5 and then filled back up to 10 prior to dry hopping - although at that point, not sure there was any sense in climbing back up to 10 prior to dry hopping.

I did toss on a pair of safety glasses just in case haha.

 

[McMullan]

The PRV on my sight-glass hop dropper is only rated for about 2 psi. So I release the pressure from the headspace of fermenter, drop the hops and quickly add co2 to bring it back to the original fermenter pressure. I do it rather quickly, but I've never had an issue with foaming. I ferment at 15 psi.

The sight glass itself should be rated much higher than 2 psi. You should be able to change the PRV. Check with the supplier first, though. If not, it’s not fit for purpose.it’s The tendency to foam is probably related to yeast strain used. My top croppers start foaming up quite quickly (<1 minute). Pretty exhilarating in panic mode.