Ferm -> cold crash/DH keg -> Serving keg

I've done this, with a hop cage in the first keg. Also, the first keg is hooked up to a couple PSI of CO2 to prevent a temperature induced drop in pressure that might otherwise encourage the lid O-ring to lose its seal.

 

If I understand you correctly this is my method, so it's not silly to me.

I cold-crash in keg only . . . if DH'ing I add the hops (in muslin bag) to keg before the transfer. Fill the keg through the liquid post (bottom up) and send to keezer. Sometimes I carb while DH'ing, sometimes I wait. But I don't pull the hops, instead jump to a fresh keg to serve. I mean, what's another keg to wash, right? While my judgment is subjective, I feel like oxidation is way down the list of problems for me.

 

I’ve done this as well. I wanted to reduce chances of oxidation and not have to leave hops in serving keg for the duration of serving. This processed seemed to work for that, just a pain to have another keg to clean.

 

Is it ok to cold crash and dry hop in the same vessel? Isn’t the whole idea of cold crashing to drop the yeast from suspension and then rack off of it before dry hopping? Even with the yeast at the bottom, would it still be harmful to dry hops?

 

As others have said, it is a solid process.

You can also dry hop, cold crash and serve all from the same keg. I do this for my IPAs, using a SS mesh cylinder to contain the hops. The hop character is a bit harsh to start (which I’m ok with), but it smooths out pretty quickly. The upside is only one transfer.

BTW, I put the hops in the keg, and then purge with repeated flushes of CO2 before transferring the beer, which I do through the liquid out post. I have no oxidation problems doing it this way, even though it typically takes me several months to finish off a keg.

 

This has happened to me a couple times and it is very demoralizing

 

Just like moving a chair halfway to the wall, and repeating ad infinitum, you never reach the wall. But you can get very close. Here's a theoretical chart based on the "purge equation":

When I dry hop in the keg, I purge the keg (already containing hops in a cage) with repeated pressurize and release cycles, then do a closed xfer into that keg.

 

You bet . . . but there's more practical workarounds. If you fill the keg with water you have purged all the air except what remains in the posts. Push out a cup full, then do a couple of purges and you will minimize even this small amount of air, then continue pushing the water. Total gas used: one volume and you can let it end up with something very low, like 1 - 2 psi. This is an extreme measure but it works.

A word on purging: Vikeman's chart is nice, but you can work the problem in your head. One atmospheric pressure is 14.7 psi (what we call zero). If you purge at 14.7 (call it 15) you will have mixed the CO2 equally with the air (given time to diffuse). In a near full keg (~1" of headspace) the diffusion will happen quickly. When you vent this mixed gas you will end up with a mixture that is half CO2 and half air. Another purge will cut the air to a quarter, another purge will give you an eighth. If you purge at 30 psi the fractions are 1/3, 1/9, 1/27th. If you have done the extreme "water purging" I described above you are looking at a fraction of the air that was in the posts . . . of which 21% is the dreaded oxygen.

Yes, that's crazy. Once your keg is purged you can add the hops with little to no air ingress. If you open the lid, then go measure your hops, find the weight for the bag, tie the string, answer a few texts . . . then yes, air will start to re-entry the keg. But you can add the hops and re-lid in less than 15 seconds if you're ready.

I did this extreme method several times and kept notes. My results were no noticeable difference than a more normal method of sanitizing/purging. I went back to filling the keg with ~1 gal of starsan, slosh, and vent. This gets rid of 20% of the air (1 gal starsan in 5 gal keg). If feeling enthusiastic do one 15 psi purge which cuts it to 40%. As the keg is filled, this 40% mixture of air is pushed out until only about 1" of headspace remains. Yes, the beer is in contact with this mixture as it's being filled but I find this not to be a problem.

Transferring: your tubing from fermenter to keg needs to be free of air. Easiest way for me is to leave the keg at ~2 psi and hook the connection to keg's liquid post first. This will vent the keg through the tubing, if it's sanitized expect lots of starsan bubbles. I fill my keg with lid closed through liquid post (PVR open), ideally all the tubing is free of air. When complete, I purge the headspace which is ~1" or about 4% of the volume of the keg. Three or four burbs and I rarely to never have oxidation problems.

Pulling hops: If you open the lid and pull the hop bag you are guaranteed to allow air to enter in a volume equal to the volume of the hop bag. Instead, jump the beer to a fresh keg (purged) and no exposure to air. What's another keg to clean, right?

With your paranoid try the water-filled method, it's only a waste of 10 gals of water and two volumes of CO2 at 2 psi which is not much. Oh yeah, some will post that filling a keg with tap water (after it's been sanitized) will expose the beer to a possible infection. I have never experienced this. In the unlikely case there are hungry microbes in your water you are exposing them to beer with a low ph and high alcohol . . . a tough environment to survive. But if still worried go ahead and use a full 5 gals of starsan.

 

Am I the only one that purges the keg with CO2 from fermentation? I skip the filling with sanitizer, seems unnecessary. Am I wrong?

 

Yeah, don’t do that. It’s ok to open the lid and add hops to a purged keg. Just do it quickly with minimal splashing and hook up your CO2 to the keg while you do it to minimize the Ingress of O2.

 

I've done this. But not when dry hopping.

 

When I force purge, I usually do it 6 times at 30 PSI. Sometimes more for a particularly delicate style. Per the chart, 6 cycles at 30 PSI lands you at about 265 ppm O2 by volume (of the total gas in the keg). But let's put that into some kind of perspective about what that means in O2 ppm for the beer.

A typical corny keg has about 20 liters internal volume. So, how much O2 (weight) is in those 20 liters after purging 6 times at 30 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 chart that the concentration of O2 after the 6th purge is about (265/209500) or 0.1265% the original concentration. 0.1265% x 5.67 grams O2 = 0.0072 grams O2 in our purged keg,

Now, when the closed transfer pushes 19 liters of the headspace out, I don't have a way to calculate how much O2 dissolves into the beer during the transfer. It would depend on how long it takes and the amount of turbulence. But let's say, worst case that won't actually happen, that all 0.0072 grams ultimately get dissolved into the beer.

19 liters of beer (@ FG of 1.010) weighs 19.2 kg (19,200 grams)
Add 0.0072 grams O2 for a total mass of 19,200.0072 grams.

19,200 / 19,200.0072 = 99.99996250001406 % beer
0.0072 / 19,200.0072 = 3.749998593750527e-5 % O2

3.749998593750527e-5 % x 1M parts =~ 0.375 ppm O2 in the beer.

Remember, that's worst case (and won't happen). I think that typically most (but certainly not all) of that O2 will be pushed out during the closed transfer, before it can dissolve.

Note: This is back of the envelope. F*** significant figures.

 

I basically do what @VikeMan does, as he describes here and in his latest post, but I just use ~ 12 psi @ 6 times. I also don’t do a closed transfer, but because (1) the headspace of the fermenter is filled with CO2 and (2) the fermenter drains fairly slowly (minimizing turbulence), I doubt there is much oxygen ingress via the fermenter.

So far I’ve been happy with the results.

Cheers!

 

Get a Fermzilla for basically the cost of a keg and do it all in one vessel and only transfer once to purged keg via during fermentation or with star-San . Simple