A while back I packaged, read bottled, a Koelsch. It was a delicious green beer, perfectly clear after gelatin fining, cold from the lagering refrigerator so I used the bottling calculators basing the calculations on a 32 degree beer. It came out under-carbonated.
The equations for bottle conditioning rely on two sources of carbon dioxide. The first is a contribution from the bit of residual yeast in the beer fermenting the priming sugar. The second source is the carbon dioxide dissolved in the beer. The assumption is that the beer is saturated with carbon dioxide at the temperature of packaging. A beer saturated with carbon dioxide at 32 degrees needs just a bit of sugar to prime where a beer at 68 degrees needs the full amount – very little carbon dioxide remains in solution at room temperature.
So I packaged the Koelsch using the priming equations at 32 degrees and got an under-carbonated beer. What happened? The beer was fermented completely quite a bit warmer than the 32 degrees I was “lagering” it so it wasn’t saturated with carbon dioxide. I can fix this, I take the caps off, drop a couple of priming tabs into each bottle and recap, little risk since the beer has already got a bit of carbonation, but work I didn’t need to do.
Lesson learned, let the beer warm up to room temp before bottling and use the full amount of priming sugar. There’s no question about priming that way.