Brewing has traditionally been an activity based on local materials. Agricultural ingredients—barley and hops—might be transported to the brewery from the countryside, and, with improvements in trade, from even further afield. But the heaviest and most ubiquitous ingredient, water, has always been—and still is—local.
That means that the chemical composition of a brewery’s water, which depends on local geology, has had a profound influence on the character of local beer. In particular, the hardness or softness of the water (meaning water with a higher or lower mineral content, mainly calcium and magnesium, and also bicarbonate) is behind the special qualities of beer styles we associate with particular locations.
For example, regions with high levels of bicarbonate in their water, such as London or Dublin, have become known for their darker beers. This is because bicarbonate affects the pH (acid-alkaline) of the water. Yeast don’t perform well faced with too high a pH (higher alkalinity). Brewers gradually learned that if used roasted barley, which makes a dark beer, the result was better. Though they didn’t realize it, the addition of roasted barley had the effect of lowering the pH.
By contrast, the Czech town of Pilsen has very soft water. Its purity contributed to the startling clean, fresh flavors of Pilsner Urquell, the very first pilsner beer.
Compare that to Burton-on-Trent in England, birthplace of pale ale. The water of the River Trent is very hard, and especially rich in calcium sulphate (gypsum). This allowed the town’s famous pale ales to feature the bitterness of hops so elegantly, and added a whiff of characteristic sulphur. In fact, the water of Burton is so famous that brewers the world around who want to brew pale ales may “Burtonize” their water, adding minerals to mimic the original.
Today, brewing chemists can alter the composition of any water supply to suit the style of beer being brewed. Despite the attention given to beer’s other three ingredients, the old ad got it right with the tag line “It’s the water.”