Bottle Conditioned or Bottle Conditioning is an old process that naturally carbonates the beer in the bottle using additional yeast and sugar. Both are added just prior to bottling, causing a secondary fermentation to occur, thus creating the CO2 for carbonation. This process is similar to the “Méthode Champenoise”. Beer can be carbonated one of two ways…the first being by forced carbonation, in which co2 is forced into the finished product until the desired level is met, similar to soda. The second way is called “bottle conditioning,” which is re-fermentation in the bottle, often by the addition of new sugars or even extra yeast to encourage more fermentation. You see when yeast eats sugar, it metabolizes it into CO2, and because the bottle is capped, any CO2 produced will be reabsorbed into the liquid, resulting in some delightful effervescence.
Since there is still yeast in there doing its thing, bottle-conditioned beers can continue to develop flavor over time, making them suitable for aging and often yielding a slightly yeast-forward, fruity-ester flavor profile. Bottle conditioned beers will typically have a layer of sediment at the bottom of the bottle. Some people say it adds loads of flavor, myself included. It is also loaded with B-vitamins. If you would rather not drink the sediment then try to leave the bottle untouched before pouring, make sure no particles are in suspension. Once the sediment has settled, pour the beer gently into your glass being extra careful not to disturb the sediment layer too much, and leaving behind the last ounce or two of beer. Belgian beers are commonly bottle conditioned as well as Hefeweizens.