Whereas the definition of beer style can be based on a variety of factors, it is the seemingly generic fermentation process itself that provides the platform from which the wider, recognizable characteristics of beer will emerge. Brewery fermentation is described primarily as the metabolism of a fermentable carbohydrate source, by yeast in the absence of oxygen, with the production of alcohol and carbon dioxide. While our knowledge of the details of fermentation is relatively recent, it is clear that control of the process is dependent in part not only on a thorough knowledge of yeast strain but also on the impact of fermentation vessel geometry and design that will greatly influence the way that yeast performs.