When we decide on a particular style of beer we want to brew, a lot of thought goes into the components of the grain bill, the hops we’ll use and how long to boil them, the strain of yeast we’ll use, and the temperature of the ferment. However, it seems that virtually no thought goes into how to mash that grain bill. This is a very important part of brewing and probably the most overlooked aspect of the “recipe”. The recipe, of course, isn’t just a list of ingredients but also the procedures used to combine and process them into a finished product.
The major purpose of mashing is to degrade proteins, gums, and starches in the grain to produce a wort which will suit our purposes as brewers. Different beer styles require a wort of specific properties. Some beers are supposed to be thick, malty, and sustaining while others should be thinner, crisp, and refreshing. The method of mashing you employ will determine the kind of beer you produce.
A single infusion works for many beers with today's fully modified malts but single infusion doesn't cater to many of the nuances of some classic styles of beer. In some cases, you have to accommodate the enzymes a little better.