Dry hopping in keg but doing closed transfer

I wouldn't recommend it. IMO you are overthinking the process. Think about the steps: after emptying the keg from water it is virtually "air-free". If you open lid and drop in a bag-of-hops there will be next to nothing entering the keg except the hop bag. Don't sit around with the lid open and reply to a bunch of texts or wind your watch or anything foolish like that, just open/insert/close and you'll be fine.

You are jumping the beer to a fresh keg (closed transfer) when it's time to pull the hops aren't you?

 

Another option beside the one offered by @PortLargo is to put the hops in and then flush with CO2 multiple times before transferring the beer. Cheers!

 

It takes a lot of Co2 to purge a keg completely. Way more than you think. If you’re not purging it completely the aromatic impact from the dry hops will be lost pretty quickly.

Best way to do it without wasting a ton of Co2 is to bag the hops and put them in the keg the day after you pitch yeast. Hook the blowoff up to the keg out and a blowoff to the keg in and let the Co2 created during fermentation purge the keg for you. Once fermentation has slowed significantly, unhook the keg and seal it, then transfer into the keg after thoroughly purging your lines.

 

When I put a bag of hops into a purged keg I know some O2 gets in with the hops and through the opening due to partial pressure of O2.

So feed CO2 into the dip tub at low pressure, <1 psi or so, and have the gas fitting QD hose going to a bucket of water. I wait for many minutes and say it is good to go. Wish I had an O2 meter.

 

For the OP's first question - I would sanitize your keg, dump the sanitizer, add your hops, co2 purge and then transfer. That's what I do with great success for NEIPAs. I've added up to 4oz pellets in a dry hop stainless mesh cylinder.

Thoughts on CO2 purging - I have an extra line on my co2 manifold in my keezer. I use that to connect to the beer out post (beer side ball lock coupler on the co2 line) and pressurize the keg to 11 psi and purge it 4 times with hopes of replacing all of the atmosphere in there with co2 from the bottom up.

I've had great success with this method. Others also work. I would not soak your hops in sanitizer solution at any point though. It'll probably ruin your hops.

 

It takes 16 full purges at 30 psi to completely purge a keg to acceptable ppb levels of o2.

11 psi purged 4 times doesn’t get you remotely close to fully purged. 20 cycles at 11 psi wouldn’t even get you close to commercially acceptable TPO levels.

 

Maybe, it would be awesome to be able to be able to measure what the residual o2 is in the keg before racking, I've always wondered. The NEIPAs coming out of my setup this way are really good and full of hop aroma and flavor and do not show any signs of oxidation, so even if I'm not getting to commercial TPO levels, hopefully I'm in the ballpark. Sensory wise, it seems so.

I'm familiar with the brulosophy co2 purge setup you are talking about, it would also be super interested to know what's left in that keg as far as residual o2. I wonder what 11 psi x 4 vs having the fermentation blow off into that keg is. Another thing to consider is what that is going to do to your dry hop sitting in there at 68 degrees or so for about 2 weeks with the keg venting.

Also - do you have a reference for that? You pulled a pretty specific number there, I'd be super interested in checking that out.

 

Let's look at the example of 20 cycles at 11 psi. Or let's say 20 cycles @ 10 psi, because that dilution is on the purge chart. (This will look a lot like another fairly recent post.)

A typical corny keg has about 20 liters internal volume. So, how much O2 (weight) is in those 20 liters after purging 20 times at 10 PSI?

We know that one liter of air at one atmosphere weighs about 1.225 grams. So 20 liters of air weighs about 25.5 grams. By weight, O2 is about 23.133% of air, so the O2 in those 20 liters weighs about 5.67 grams.

We know from the purge chart that the concentration of O2 after the 20th purge (@ 10 PSI) is about (6/209500) or 0.0029% the original concentration. 0.0029% x 5.67 grams O2 = 0.00016 grams O2 in our purged keg,

19 liters of beer (@ FG of 1.010) weighs 19.2 kg (19,200 grams)
Add 0.00016 grams O2 for a total mass of 19,200.00016 grams.

19,200 / 19,200.00016 = 99.99999916666667 % beer
0.00016 / 19,200.00016 = 8.333333263888889e-7 % O2

8.333333263888889e-7 % x 1M parts =~ 0.0083 ppm or 8.3 ppb O2 in the beer.

Sometimes people may look at the purge chart and think that (say) 6 ppm looks horrible. But that's the concentration of O2 in the air in the keg, not the parts per million (by weight) in the beer. In this example, 6 ppm on the chart really means ~ 8.3 ppb in the beer.

(no attempt has been made to honor significant figures on the back of this envelope)

 

Wow, thanks for providing that. If it doesn’t take much effort to look at 11 psi purging 4 times I would super appreciate that for my own information.

 

There’s a purge chart you can find online.

Normal ale fermentation should only take 6-7 days including D rest for your standard IPA. Yes hops are sitting warm for a bit but they’re also being purged of O2 at the same time. Guarantee you your hops spent a lot more time warm by the time they got to you. Especially through the standard Homebrew channels. Someone has also done the calculations to figure out how long it takes to purge a keg using fermentation. Again available online. If you’re concerned about the hops sitting warm in a keg for a while you can pull the blow offs after 4 days or so and put the keg in your kegerator/keezer until you’re ready to transfer to the DH keg.

 

I'm going to be AFK for a while, but here's the chart:

Basically, find your starting ppm on the chart, then work through the math like in my post above.

Just replace the "6" in "is about (6/209500) or 0.0029%" with the ppm number from the chart, replace the "0.0029%" with the result of X/209500 calculation and go from there.

 

cool thanks. I typically dry hop in primary day 4-5 of ferm and then let that sit for 7 days, then rack to a keg with the second hop charge so my typical ferm for neipas is 11-13 days. The keg dh gets purged of o2 with the keg via co2 flush. It’s been working super well for me, but I totally believe that other people can produce good results with a different process. I get my hops from Yakima valley hops dot com and I fridge store them. I’ll look into the charts provided. Thanks.

 

Just some empirical data here. I typically purge with CO2 six times at serving pressure, which is in the 10 to 12 psi range. This works for me as far as keeping my hoppy, dry-hopped-in-the-keg beers fresh tasting during their duration, which is typically several months. Cheers!