Carbing a keg with corn sugar

[doug293cz]

I would imagine you use less priming sugar because you desire less carbonation to avoid over foaming with pouring when using a keg.

In a bottle it's easy to carb to 2.5 volumes of CO2 and pour without too much foam. In a keg, unless you have a lot of resistance (long lines) - pouring that 2.5 volumes of CO2 might cause too much foaming.

So maybe in a keg the recommendation is to carbonate to 2 volumes of CO2 to avoid that issue?

^not science. Based on my newbie brewing logic.

I had a similar thought, i.e. that some people unconsciously prefer lower carbonation in their draft beer, so think it is overcarbed when carbed to "normal" levels. The problem with this idea is that about a week or two after hooking a keg up for serving, the carb level will be back to the "normal" level as that is the equilibrium level for the serving pressure chosen. If people set their pressures for less carb, then it would be a conscious decision to have a lower level of carbonation.

Brew on

 

[chickypad]

I had a similar thought, i.e. that some people unconsciously prefer lower carbonation in their draft beer, so think it is overcarbed when carbed to "normal" levels. The problem with this idea is that about a week or two after hooking a keg up for serving, the carb level will be back to the "normal" level as that is the equilibrium level for the serving pressure chosen. If people set their pressures for less carb, then it would be a conscious decision to have a lower level of carbonation.

Brew on

Right. I have my system set to 2.6 vols, and compared to bottled beers my kegged beers are definitely well carbonated c/w what I would expect at 2.6. Is it possible that maybe we're not chilling enough and getting the CO2 into solution before tapping, so on initial tap it seems overcarbed? Trying to remember now on the few kegs that seemed overcarbed how long they chilled. I typically do something like set the keg in the keezer for 24-48 hrs after natural carbing then hook them up to gas.
At any rate, since the 3 oz gets me close enough that I can't tell the difference and don't have trouble pouring at 24 hrs I'll probably just continue that way.

 

[Gnomebrewer]

I'm wondering if it could be the loss of CO2 from bottles that causes the discrepancy.

Assuming the carbonation is the same in a bottle as it is in the keg with the same rate of sugar (adjusting for the pressurised head space in the keg), when you open a bottle you lose the CO2 from the headspace, allowing CO2 bubbles to immediately start leaving the beer. You then (mostly) pour into a glass, which removes more CO2. On draught, the lines are balanced so you should lose minimal CO2, thus it might be more 'efficient' at keeping the carbonation.

This would mean that 2.5volumess in a bottle might only be, say, 2.0vols equivalent from a keg. Remembering that there are about 0.8vols in solution from fermentation, that means adding 1.2vols vs adding 1.7vols. Removing the volume for the pressurised headspace, you'd only need to add 1.0 to 1.1volumes in the keg, or about 2/3 of the equivalent bottle amount. It's even more exaggerated for me because I like lower carbonation - I go to about 2.0volumes in the bottle. Using the same (dodgy guesswork) maths as above, that means using about 50% of the sugar in the keg.

To test this, I might carbonate a keg using the full dose of sugar (I also bottle some off each batch - 7gal batches), test the carbonation off the keg vs. the bottle (I'm sure the keg will be too high) then take the lid off the keg and try pouring some into a jug, using it like a big bottle. Of course, once I've opened a keg like this it needs to be gone in a night.

 

[soccerdad]

I'd have a neighbor that I don't like 'take the lid off the keg' if you are not venting the co2 first.

 

[Gnomebrewer]

I'd have a neighbor that I don't like 'take the lid off the keg' if you are not venting the co2 first.

Yes, the CO2 will be vented first.

 

[onno]

I’m hip to what gnome brewer says. There is a noticeable difference in carbonation when drinking from the bottle vs pouring it into a glass. If beer on tap delivers that carbonation it could help to account for the discrepancy between the math and practice.

 

[DJL531]

I recently started kegging. I have 3 gallon kegs and brew 2.5 to 2.75 gallons of beer. My 3rd keg is a Munich style lager and I chose to prime it with 1 oz of dextrose. I sealed the keg with 10-12 psi of CO2 and I've tasted it twice. It has carb, needs a little more, clear and no sediment on the first 2 6 oz pours. Will place in fridge this weekend and then hook up to CO2 at serving pressure. I'm hoping the extra carb and cold will give it a little more mouthfeel than I get at room temp, 70 deg that is.