I'm thinking of buying a CO2 bulb and holder to fit a 25 litre keg. I have the right cap to fit one.

Am I right in thinking the only purpose is to stop air ingress through the tap (that would cause taints) ? Or will it also contribute to carbonation ?

I use honey or brew sugar for priming in the keg. Beer is fairly fizzy when it comes out but goes still quite quickly.

1 Answer 1


IMHO the answer is a both. The CO2 from the bulb contributes to carbonation in that it keeps a atmosphere of CO2 over the beer and keeps it under slight pressure. It also a prevents a partial vacuum developing above the beer while its being poured from the keg. Without a CO2 bulb supplying the CO2 to fill the keg, one would have to admit air to allow the beer the flow freely.

  • okay, sounds like i need one. Commented Nov 9, 2017 at 8:58
  • To a large extent it depends on how carbonated you like your beer and how quickly the barrel will be emptied. If you like less carbonated ale and there is a party happening or the keg is being stored cold then the beer might be acceptable without any CO2 additions/help. However if the beer will be consumed over some weeks then a CO2 bulb is a useful addition. Commented Nov 10, 2017 at 8:54

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