Brett beers not carbing well

I have done several Brett beers, both with Brett as a Primary yeast, and some with Brett as a Secondary yeast. When using it as a Primary yeast, it has been 3 to 4 months in the fermenter before bottling. When using it as a Secondary yeast, it has been left for about 12 months before bottling.

I have primed the same way I do normal ales.

I find all the beers are carb'd, taste great, but do not form much of a head (if any). The beers are not flat.

There is obviously yeast available as none of the beers are flat. I have been using between 5 to 5.5 ozs of cane sugar for priming 6.5 gallons.

My Pale Ales and Belgians carb really well, form a decent head when pouring and keeps it all the way to the bottom of the glass.

I am wondering if the long time in the fermenter is the reason for the relatively low carbonation. Due to the long time sitting in the fermenter, the entrained CO2 is less than assumed for a normal beer.

Should I be using more priming sugar due to the long time sitting? Is there any way of figuring out how much entrained CO2 is lost over time?

Are you adding more yeast to the beer when you bottle? Especially so with the 12month beer you should certainly add something or just be real patient and allow 4-6 months for full carbonation. With the year old brett beer there is certainly viable yeast but the cell count is likely so low that it will take a long time to carb the beer. Many beers are bottle conditioned with a 750k-1mil yeast/ml of beer. Fully fermented beers especially at a year of age will likely have substantially less yeast. I don't think its a case of needing to add more sugar it's just a case of cell count and patience. I bet if you popped a few of them open and gave a serving of yeast with a pipette you'd have carbonated beer in a few weeks.

Some of these are almost a year in the bottle and doing the same thing.

I figured Brett stuck around longer than Sacc, and would be OK.

They are carbonated, but to a low level. Not flat, there are bubbles rising to the surface all the while it is in the glass.

Bottles that are about 12 months, are similar to ones that are 3 months. I think they have consumed all the sugars.

Probably could do with a yeast boost on the ones that sat for a year, and will try it when I bottle some in the next few weeks.

Standard priming levels assume an amount of dissolved CO2 in the beer. I'm wondering if beers left a long time lose some of that dissolved CO2, and if so, how do you figure out how to compensate for it.

I think the standard calculators assume there is 0.6vol of Co2 left in solution for your beer, during extended aging the beer off gasses lots of co2 until it comes to an equilibrium with the atmosphere + any co2 currently being produced.

You also need to enter the warmest temperature the beers ever reached into the calculator, as high temps will also drive out more Co2. Generally I set the priming calc to 85F and carb to the midrange of the co2 levels, and they come out nice and fizzy

I have the same issue with a saison that I fermented with White Labs farmhouse blend, which includes brett. I didn't even let it sit that long - it was in the fermenter for only about a month(that blend packs a pretty intense brett character fairly quickly - me likey). And I used a little bit more corn sugar than usual for priming, since I wanted a pretty high level of carbonation. But now it has been in the bottles for about 6-7 weeks, and still very low carbonation and next to no head formation or retention. I know some beers take longer than others, but it does not really seem to be progressing. It's not much more carbonated now than it was after 2 weeks in the bottle (the last time I sampled). I wouldn't say that it is flat, there are a lot of tiny bubbles that rise to the surface throughout drinking a glass. But it's definitely not what I would call lively either. There is not even much of a hissing sound when I crack open a bottle. Is it common for beers with brett to take a really long time to properly carbonate even without sitting in a fermenter for an extended time, or is this as good as it's going to get?

*edit - I should also add that this is not a very big beer either - only about 5.3% ABV. So I know that the slow carbonation is not due to it being a really high gravity beer. This is by far the longest time any of my normal strength beers have taken to show good carbonation.

My brett beers are carbing up just fine. In fact I think the 11-11-11 old ale is a tad overcarbonated. I added malt extract but calculated it as priming sugar for 100% attenuation instead of 75% like most DMEs. My saison I slightly underprimed so I could get it into bottles and let the brett bring it up a few more points as it ages. The saison is coming along nicely, it was the ECY03 blend. The old ale was WY9097.

I've mostly stopped using priming sugar calculators. It's really easy to figure out by hand and this allows you to choose for lower levels of residual carbonation. A Primer on Priming