How long has it been in the bottles? What Temp are you storing them at? What was the OG of the beer....all these factors come into play as to rate of carbonation.
If a few bottles are carbed and some aren't, really isn't about improperly mixed solution...it really mixes itself pretty well...it usually really means the beers not ready yet...each bottle is it's own little microcosm, some even right next to otheres may merely be a tad warmer, and THAT could affect why one beer is done carbing and the other isn't. Waiting another week, and you will more than likely have them ALL carbed...
I have had beers take 8 weeks to carb and condition...It's a natural process...so it has it's own agenda based on the OG of the beer AND the temp of the bottles...It is ACTUALLY theoretically possible to not add any priming sugar
and with time to have the beer carb up (for lower grab beer like yours) In fact old english brewing books have recipes that DON'T add sugar...I ran some of the recipes though beersmith, and that corroborated that fact.
You just need more time, that's all I never worry unless it's 8 weeks for a normal grav beer..heck my 1.090 OG Belgian strong took 3 MONTHS
Revvy's Blog, Of Patience and Bottle Conditioning.
Lazy Llama diagramed it best...
Beer under 8 weeks is still WAAAY within my not worry zone...especially if the beer is below 70 degrees.
And yes bottle size does come into play...Larger bottles take longer than smaller ones. I have some pints, 22 oz bombers and other sizes that I often use, but since I enter contests I usually also do a sixer or two of standard 12 ouncers for entering. And inevitably the 12 ouncers are done at least a week faster than the larger bottles....some times two weeks ahead of time...
Big Kahuna once gave a good explanation..
Originally Posted by BigKahuna
Simple. It's the ratio of contact area just like in a keg. The c02 will need to pressurize the head space (Which takes LESS TIME) in a bigger bottle (More Yeast and sugar, roughly the same head space) but then it has to force that c02 into solution through the same contact area...thus it takes longer.
You'll find that many people have observed that larger bottles take longer...And comparing 2 at the same time often results in a different taste, becasue they are conditioning at different rates...
Hope this helps.