Tuesday, 16 August 2016

On splitting KeyKegs

I had a few 30L slimline KeyKegs split on me after filling which, especially for our first kegged gyle, cost us a lot in lost revenue just when we needed it least. After tweeting about the problem I had a whole heap of helpful advice from other brewers who had been through the same, and on seeing these tweets, further advice directly from the manufacturer. This post captures that advice for the benefit of others as it helped me to (so far, at least!) eliminate the problem.

First, to be clear on 'the problem', the photo below shows a KeyKeg where beer has leaked into the space between the bag containing the beer and the plastic outer. KeyKegs are dispensed by pushing gas into this space to force the pre-conditioned beer out of the bag. Technically the keg is still useable in the state shown but you'll probably struggle to get all of the beer our and of course, they can't be sold to trade looking like that. The problem seems specific to the newer slimline kegs. The old round ones don't seem to exhibit the same, at least based on feedback I've had.

One cause of this problem is reported to be under-filling although apparently there are other causes too (not covered here). KeyKegs are filled upside down then turned the right way up once full. The theory is that if even slightly under-filled, once turned the right way up, the beer in the keg will pull down on the top of the bag as the beer fills the space that was at the top of the keg when it was upside down. I found that the ones I had split did so a day or two after filling whilst sat on a pallet undisturbed.

I'm filling the kegs by gravity. I'm doing that as we have open fermenters with lids rather than cylindro-conical models which can deal with pressurised gas in the headspace to 'push' the beer out of the tank. My method is to pump the finished chilled beer into an IBC sat at around 2 metres above the floor, then batch prime it to the desired carbonation level before filling the kegs.  The advice I got was as follows:

  • Ideally fill under pressure to ensure some force behind the beer as its pushed into the keg. That's KeyKeg's recommendation from the outset. Not an option for us without buying another tank, though.
  • Ensure the filling head is fully engaged into the keg shaft before opening the fill valve and apply the head carefully being sure not to 'tug' at the head to engage it as the top of the bag can move within the keg. Food grade lube was suggested to assist this but I think as long as the head is fully 'open' before rotating it, it usually goes into place with almost no resistance. I was still getting splits after confirming good head engagement, however (although reduced)
  • Ensure the keg really is full after filling. I played around with this a bit and found that I could get a few more grammes (or ml) by re-applying the head after turning the keg the right way up. They should weigh 31.4Kg when full, or thereabouts. The bag should be visibly 'full' with no gaps (other than small creases, this is expected) visible from outside the keg. 
  • Use a pump to assist when filling by gravity, to help ensure the keg really is full. Again, I played around with this by filling through a small pump (that was off) until the bag stopped visibly and audibly expanding then turning the pump on. This really helped get more beer into the keg and on turning the pump on I saw the bag visibly expand further to fill any remaining space. Since doing this, kegs are filled reliably to 31.4Kg and I've experienced no further issues with splitting.

A photo of my filler setup is shown below. It uses a small DC mag pump (this one) in-line before the filling head. I turn the pump on after opening the filler valve and turn it off again after closing the valve after filling. This has the added bonus of filling the kegs about 2-3 times faster than by gravity alone.

If anyone has any other tips or findings, feel free to share them in the comments below. 

I should note that some breweries have reported occasional failures both when filling under pressure or by gravity, even if the keg is entirely full. This should of course be referred to your supplier or the manufacturer directly. I'm only writing about my own experiences here which appeared to be caused by under-filling.


  1. I was talking to the guys at Fourpure a while back and they told me there had been a recall on a batch of KK as there had been some sort of malfunction. Might be worth having a chat with them about it.

    1. Cheers Glyn. I recall talking to Dan about that a while back (when they first started using slimlines). Hopefully covered that in my footnote.

  2. We messed around with kk a while ago (the old spherical kind). And, as you suggest, we didn't have this problem. Mind, we made sure the shell was pressurised, and then pumped beer in (with a flojet, as it happens), controlling the flow by bleeding off the gas port. That seemed to work pretty well.

    1. I've not heard of anyone having the issue with the old ones but I'm pretty sure the same approach you describe would reliably fill the slimlines and avoid splitting due to under-filling.

  3. Andy, if you're using a pump, can't you now fill them upside down?

    1. I've always filled them upside down, just before I had a pump I found I could get a little bit more in by turning it back the right way up once it was 'full' upside down. They should always be filled upside down of course.

    2. Ah, of course you are - I misunderstood the "filling by gravity" bit, despite having a basic working knowledge of physics.

  4. Great read as always Andy.

    1. Thanks Wayne - hoping it may help others avoid problems.

  5. Do they have to be full? I'm about to fill 25litres into a 30l slimline. If not I may need to swap the kegs to 20l versions instead. Help needed

  6. I am looking at using KK and would like to export, can anybody give me advice on what type of priming sugar, and how much. I have been advised that Glucolose, from Murphies is the best.


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