So do people have a rule of thumb for when it's necessary to re-pitch some fresh yeast in order to carbonate a higher gravity beer via bottle conditioning? A gravity threshold, or length of time in secondary, etc? For reference, here is my situation. I've brewed my first higher gravity beer, an Imperial Stout with an O.G. of 1.105. I pitched onto a Wyeast 1056 yeast cake from a previous beer, it was in primary for a month, has been in secondary for another month, and I plan on bottling it soon so that it has plenty of time to carbonate and bottle condition before Christmas time. It was at 1.020 when I racked to secondary. The chapter in How to Brew on priming and carbonation doesn't really address the issue, but in the common problems section is says that for a long aged beer, there might not be enough viable yeast left for carbonation.