 When the concentration of fermentable sugars in the beer falls below a certain level, variable with the strain of yeast, the yeast cells will naturally flocculate and settle toward the bottom of the vessel in which the beer is stored; this act is known as "dropping bright".The degree to which yeast flocculates is dependent on many factors, including the specific gravity of the beer, the gas pressure over the beer, the ambient temperature, and some biological properties particular to the yeast strain; some beers will never drop bright by themselves.Some breweries make available "rack bright" beer, which is cask-conditioned beer that has dropped bright at the brewery and then "racked", transferred, to a new container for shipment.