keg priming question

hello. i ordinarily force carbonate my kegs, but i'm preparing to age a dubbel for about 6 months and would like to prime this time. my question is this: why is less priming sugar required when kegging than when bottling? i've been brewing for about 10 years and have never seen an adequate explanation. i do not buy the explanation regarding headspace, since, while the headspace in a keg is large, it is roughly proportionate to the headspace in a bottle, given the greater total volume. it seems to me that for a given volume of beer with a given yeast count, a quantity of priming sugar should yield the same level of carbonation regardless of packaging. is there something in the cooperation of yeast when in a larger volume (like the keg) that i'm not considering? the last time i primed a keg using the prescribed 1/3 cup, the beer was undercarbonated. has anyone had this experience?

I suspect it is a compensation for the pour. I run most of my ales at 8-10 psi, which is less than two volumes and get a nice head & residual carbonation. One probably loses more CO2 pouring from a bottle. Just a guess, as I don't bottle or prime my kegs.

Sounds like it needs RESEARCH, the kind you get government grants for.

I share your curiosity. I also have never heard a good explanation.

I recently started kegging, and the last time I kegged a batch, I forgot to adjust the amount of priming sugar. Of course, after sealing the keg and realizing what I did, I panicked.

You know what, the beer was fine. Perfectly carbonated.

I always assumed it was because priming was the only way to introduce CO2 to bottles. When you keg, you will be adding more CO2 to serve. I would guess that even at low pressure someof this would go into solution in the beer and if you primed the keg with the normal amount of sugar or DME then this would result in over carboration if it sat on the bottle for awhile.

Just a WAG

Pressure is pressure. I don't think the beer could carbonate to a higher level than set at the reguator regardless of the source.

thanks for the replies. i think any of those explanations sound viable, but maybe more contributing factors than the primary one. i think you'll lose some gas either way on the pour, and the regulator should take care of pumping any more (excess) gas into the already-conditioned beer.

sonvolt, it's interesting you had that experience with the regular amount of priming sugar. it seems to go along with my under-carbonated kegs when using the recommended 1/3 cup. can it be that all these brew books are simply giving bad information? since most keggers force carbonate, are they just unfamiliar with this more unusual procedure? i'm curious if anyone out there has had adequate carbonation from the reduced priming quantity suggested by the books.

of course, the beauty of kegging is you can adjust the carbonation up or down at any time. i'd just like to get it more or less in the realm of a bottled dubbel.