100% re-fermentation or bottle conditioning means that the beer is bottled flat and gets all of its carbonation from the re-fermentation in the bottle. Partial re-fermentation, which is frequently referred to as bottle-conditioned, involves taking what is often flat beer, and adding carbonation to it first before adding a small amount of yeast and sugar to complete the process. As such, most bottle-conditioned beers are only partially bottle-refermented. 100% bottle-conditioning is now rare, but results in far greater complexity and aging ability.
