Last few pints in keg taste much different

[slurms]

I'm about to kick my first keg. I've got maybe 2 or 3 more pints left in it (was 3 gallons of an APA). The beer tasted fine throughout the month or so I had it. On Friday I had a pint or two and it tasted fine. The next day, I pulled a small sample just because I wanted a little beer, and it tasted MUCH different. It looked darker with muted hops flavor, which leads me to oxidation. But can that happen LITERALLY overnight? That doesn't seem likely. The flavor didn't seem to be changing over the course of its life, I would think it would be more and more noticeable.

Is there something with kegging that causes the last few pints to taste odd? I would think all the crap that's in the beer that settle out would be in the FIRST few pints, but I didn't notice that this time. I have a normal dip tube, not a floating one. I also noticed that the beer started to foam a lot after Friday (likely over carbonated due to the smaller volume being able to cool down more than the original 3 gallons?).

Just a side note, this beer actually turned into a slushy when I first put it in the kegerator. Was my first time using this homemade kegerator but since got that sorted out. Don't think that could lead to the last few pints to taste odd.

 

[MrPowers]

Did you discard the beer that was sitting in the serving line first? Line beer will oxidize literally overnight (unless you are using special tubing). Next taste, discard the first few ounces and see if you still have a problem.

 

[McKnuckle]

I have had this happen when using a floating dip tube, although I see you've issued an explicit caveat that you aren't using one. In that case, muck at the bottom has never been ejected from the keg, so it sits there waiting for you.

I've had it happen with a couple of normally dipped kegs as well, just not often or badly enough for it to be notable.

There is always some amount of permanent muck at the bottom of a keg, even with a normal dip tube. Just like when we rack out of a fermenter, the clear liquid flows first, but once its volume significantly decreases in proportion to the remaining trub, the trub starts encroaching on the racking device's inlet. I imagine the same is happening to you with this keg. Not something you have to take action about.

 

[slurms]

Line beer will oxidize literally overnight (unless you are using special tubing). Next taste, discard the first few ounces and see if you still have a problem.

That's interesting. No special tubing, and I haven't been discarding the first few ounces since it tasted fine up until now. Wonder if that has always been oxidized but was covered up with 90% of the pint coming from the bulk of the keg covering up the flavor. But with a few pints left, the line oxidizes and impacts what's in the keg faster b/c of the less volume in there.

Just like when we rack out of a fermenter, the clear liquid flows first, but once its volume significantly decreases in proportion to the remaining trub, the trub starts encroaching on the racking device's inlet.

That makes sense when racking, since we purposely put the racking cane in the middle of the fermenter to purposely rack the clear beer. It is still up to us how much trub we rack. But with a permanently placed dip tube, it's always pulling from the bottom where all the trub will be after sitting in the keg. So I would think the first few pints would have most of the trub, with the rest of the keg getting less and less. Although to that point, I don't remember much suspended stuff in the first few pints...

Thanks for the replies so far!

 

[MrPowers]

That's interesting. No special tubing, and I haven't been discarding the first few ounces since it tasted fine up until now. Wonder if that has always been oxidized but was covered up with 90% of the pint coming from the bulk of the keg covering up the flavor. But with a few pints left, the line oxidizes and impacts what's in the keg faster b/c of the less volume in there.

I think your assessment is right on. You mentioned you had a small beer rather than a pint. In a pint, the line beer would be diluted with enough fresh beer from the keg so you may not notice it. In a small glass, you will have proportionately more line beer and are more likely to notice the oxidation. Keep in mind, you don't need to pour off line beer every pint, just before the first pint after the keg has sat for awhile.

Oxygen permeability of your beer and gas lines can absolutely affect the beer in the keg, and that effect does get more pronounced with time, but in this case I think it's probably just line beer.

 

[McKnuckle]

That makes sense when racking, since we purposely put the racking cane in the middle of the fermenter to purposely rack the clear beer. It is still up to us how much trub we rack. But with a permanently placed dip tube, it's always pulling from the bottom where all the trub will be after sitting in the keg.

The phenomenon I mentioned is observable. I have a couple of fermenters with spigots attached to rotating racking arms (dip tubes). I leave them pointed fully down during the transfer process, and what I described definitely occurs. Once the wort clears away, the trub encroaches.

The same thing occurs if you gently rest your auto-siphon on the side/bottom of the fermenter once it gets going. Trub doesn't get pulled in until the end, even though it is there all along.

 

[slurms]

You mentioned you had a small beer rather than a pint. In a pint, the line beer would be diluted with enough fresh beer from the keg so you may not notice it. In a small glass, you will have proportionately more line beer and are more likely to notice the oxidation. Keep in mind, you don't need to pour off line beer every pint, just before the first pint after the keg has sat for awhile.

Yes, that makes sense. What doesn't entirely make sense to me is that I've pulled small glasses previously, after at least having the keg sitting overnight (if not longer) and it tasted fine. After the bad tasting taster glass, I pulled a full pint as well with the same flavor. Maybe it still has something to do with oxidation but it's odd that it would be from the line beer after it's been cleared out.

I have a couple of fermenters with spigots attached to rotating racking arms (dip tubes). I leave them pointed fully down during the transfer process, and what I described definitely occurs. Once the wort clears away, the trub encroaches.

Maybe I don't understand your set up. If you have a spigot at the bottom, with a racking arm pointed downward, wouldn't that be entirely in the trub? Shouldn't that be pointing upward to get away from trub? Unless you're in a secondary and there isn't much there anyway. I rack from primary into the kegs with an auto-siphon, held in the middle of the fermenter (pulling clear beer), and slowly lower it down until there isn't much left. Once I start pulling trub, I stop. Yes I get some from down there, and whatever is still floating in the beer, but I would think that is minimal. And after the keg is cooled for a while and everything settles, then the crap that got transferred in would be gone in the first few pints.

 

[McKnuckle]

I have an Anvil fermenter, and yes, the arm points downward perpendicularly to the bottom of the vessel. I do not rotate it when I rack. There is a smidge of trub that gets sucked up immediately when I open the valve, then it's smooth sailing for the entire transfer until the very end, when the available beer dwindles to a smaller circumference than the sediment. And then the sediment starts moving.

Actually, they designed this particular fermenter well, because it loses siphon at that point nearly every time, and I don't even have to stop it myself.

Anyway, this phenomenon might not be happening to your kegs, but I thought it was a helpful thought to consider regardless.

Keep in mind - this is your first keg and it's not empty. Wait til you clean it, and then you can evaluate this for yourself.

 

[slurms]

Ahh, that makes a lot more sense. I was thinking a plastic fermenter with the spigot near the bottom, and then a dip tube just immersed in the gunk at the bottom. Your advice makes much more sense now haha

Given there's maybe only a few pints left (from what I can tell that sloshes around), I might just call it quits with this one (assuming the next sample after clearing the line tastes off), and then see what I'm dealing with inside of there.

 

[MrPowers]

Yes, that makes sense. What doesn't entirely make sense to me is that I've pulled small glasses previously, after at least having the keg sitting overnight (if not longer) and it tasted fine. After the bad tasting taster glass, I pulled a full pint as well with the same flavor. Maybe it still has something to do with oxidation but it's odd that it would be from the line beer after it's been cleared out.

In that case, yes you are likely dealing with something else. It could be oxidation in the keg from oxygen left in the headspace after kegging/purging, it could be impure Co2, or it could be ingress through the lines. It could be something completely different. How long has the beer been on tap?

 

[slurms]

I believe I kegged this batch at the end of October, so it's been a little over a month in there. This was an open transfer from fermenter to keg (working on getting closed transfer going soon). Like I said, this was 3 gallons. I purged the keg 2-3 times but given the large headspace, I didn't want to waste too much CO2 with doing so. Just so strange it happened so quickly, like, over the course of 12 hours. Tasted fine and then bam, not fine.

The batch after this one was 5 gallons (of a porter), so purging the headspace was less wasteful. However, I'm ashamed to admit that I didn't realize the tube came off the bottom of the keg, so a gallon or so was just splashing in until I fixed that (lesson learned). Hoping the effects of any oxidation are hidden under the porter flavors... But, I'm waiting on parts for closed transfer so HOPEFULLY that kind of oxidation is out of the question.

 

[MrPowers]

I believe I kegged this batch at the end of October, so it's been a little over a month in there. This was an open transfer from fermenter to keg (working on getting closed transfer going soon). Like I said, this was 3 gallons. I purged the keg 2-3 times but given the large headspace, I didn't want to waste too much CO2 with doing so. Just so strange it happened so quickly, like, over the course of 12 hours. Tasted fine and then bam, not fine.

The batch after this one was 5 gallons (of a porter), so purging the headspace was less wasteful. However, I'm ashamed to admit that I didn't realize the tube came off the bottom of the keg, so a gallon or so was just splashing in until I fixed that (lesson learned). Hoping the effects of any oxidation are hidden under the porter flavors... But, I'm waiting on parts for closed transfer so HOPEFULLY that kind of oxidation is out of the question.

I would google a guide to proper keg purging. There are several methods of doing it (opening prv, sanitizer purging, etc...), each with varying effect, but you would be surprised how many purge cycles it takes to get the O2 levels down in the keg to "shelf stable" levels.

I agree that it is strange that it turned literally overnight, but that is not unheard of especially in hoppier beers.

 

[J2W2]

I believe I kegged this batch at the end of October, so it's been a little over a month in there. This was an open transfer from fermenter to keg (working on getting closed transfer going soon). Like I said, this was 3 gallons. I purged the keg 2-3 times but given the large headspace, I didn't want to waste too much CO2 with doing so. Just so strange it happened so quickly, like, over the course of 12 hours. Tasted fine and then bam, not fine.

Little late to the party, but I'll add my two-cents worth. I've had beers in the keg for up to a year - rare, but it happens. And yes, the flavors change over time. I've had a porter turn into more of a seasonal, picking up some new flavors as it ages, but still drinkable. An IPA would not handle this timeframe, hops do not age well, but that's never an issue for my IPAs! Anyway, under normal circumstances, I would not expect an APA to change flavors this quickly.

On the other hand, I'm always amazed at the amount of sludge that can build up in a keg. Mine have dip tubes that go all the way to the bottom, and my beer is clear until the last pint, which can suddenly become extremely cloudy, right before the CO2 starts blowing through. I'll never even think about drinking the last pint, it goes right down the drain. I think there must be some sludge floating on top as well as collecting at the bottom, so that's what comes through on the last pint. I really feel that way with IPAs - I think there's some hop oil, etc, floating on top.

The batch after this one was 5 gallons (of a porter), so purging the headspace was less wasteful. However, I'm ashamed to admit that I didn't realize the tube came off the bottom of the keg, so a gallon or so was just splashing in until I fixed that (lesson learned). Hoping the effects of any oxidation are hidden under the porter flavors... But, I'm waiting on parts for closed transfer so HOPEFULLY that kind of oxidation is out of the question.

A closed transfer will save you a lot of headaches. I completely seal up a keg with some sanitizer in it and roll it around to catch all the surfaces. Then I shoot some CO2 into it and spray some sanitizer on the lid and posts to check for leaks. Finally I hook up a short tube with a liquid disconnect to purge the sanitizer, then connect the short tube to my fermenter spigot (I have a SS Brewtech Brew Bucket), partially unscrew the pressure relief valve on the keg lid (to allow air to escape) and fill the keg using the liquid dip tube. That results in pretty much zero splashing.

One last note, while purging the keg's headspace may seem wasteful, it doesn't use that much CO2 - on a five-gallon batch - and it's definitely good practice. I'll usually purge mine five or six times after I fill a keg. Remember, that headspace gas is being forced into your beer, and you definitely don't want to be forcing oxygen in. So yeah, you may have definitely oxidized your three-gallon batch.

Good luck!

 

[slurms]

I appreciate everyone's input. All makes sense.

After consulting with the keg, it turns out there was a good amount of gunk that settled out and must have gotten picked up as the volume dwindled down to a few pints (@McKnuckle, ya might be on to something with your theory in this case). I'm going to chalk this one to just sediment at the end of the keg.

Cheers!