Why is the pH of beer reduced?

Beer, like all other alcoholic beverages, undergoes a process of fermentation, in which sugar is converted to alcohol and carbon dioxide. The fermentation process is initiated by the presence of microorganisms, such as yeast. Yeast metabolizes the sugar in the beer to produce alcohol and carbon dioxide. During this process, the pH of the beer is lowered.

The purpose of this is twofold. First, it helps to prevent the beer from becoming sour due to the growth of bacteria. Second, it limits the amount of souring agents that can be produced by the yeast. By limiting these factors, you are able to achieve a smoother, more refined taste in your beer.