What defines real ale?

Real ale is defined as a naturally brewed product that undergoes secondary fermentation in the cask from which it is served. This traditional method emphasizes the use of natural ingredients and a fermentation process that is reliant on yeast rather than artificial carbonation. The use of live yeast in the cask allows the beer to mature and develop complex flavors over time, making real ale distinct from other types of beer that may rely on pasteurization or forced carbonation for stability and shelf life.

The other options do not align with the principles of real ale. For instance, pasteurization alters the character of the beer and is more commonly associated with commercially produced lagers. Artificial carbonation contrasts with the natural fermentation process that real ale champions. Serving beer only in bottles also does not adhere to the traditional cask conditioning that defines real ale, as it can be offered on draft or from cask as well. Thus, the focus on natural fermentation and maturation in cask is what solidifies real ale's identity in the brewing world.