Originally Posted by Iordz
If you see “bottle conditioned” on a beer label, it means fresh yeast was added during bottling to ensure carbonation.
It is not necessary to add more yeast, and I believe most of the bottle conditioned ales do not add more yeast. However some brewerys filter their beer before bottling then add a different yeast for bottling. In particular a lager yeast might be added to an ale so it will carbonate even if the beer is stored cold.
For the home brewer it is only necessary to add yeast at bottling if your beer has been in the fermenter for 6months or more. Even then it will probably carbonate but it may take a long time.
There is not much sugar being added at bottling so it does not take much yeast. If you feel you need to add yeast a Wyeast pack or WhiteLabs tube is more than enough yeast, as is a half packet of dry. A starter is not needed in this case. The yeast can come from any safe source. Because there is not much fermentation happening in the bottle the type of yeast is not of much concern. The easiest and perhaps cheapest solution is to use a packet of dry yeast.
Dubbles and Trippels do not really refer to the number of fermentations. That is just a tale propagated by many consumers. They only refer somewhat loosely to the strength of the beer with Dubbles being a strong beer and Trippels being even stronger.