"This is why the Burton waters were so good for brewing," Dr. Maltman said. "It turned out they had a very high mineral content, but just in the right balance to get the right acidity for good leeching, good mashing. The balance of fermentable sugars has everything to do with the flavors and the kind of beer that results. The mashing stage is crucial."

The water was also rich in sulfates, which acted as a preservative, allowing the beer to be shipped to distant locations, even India -- the Burton beers were called India pale ales, or I.P.A. for short. "The I.P.A. style came about because of the geology on which Burton was sited," Dr. Maltman said.

Today, any brewer anywhere can produce India pale ales by adding minerals to -- or "burtonizing" -- the water to match what burbles in Burton-on-Trent naturally.

A new style of beer called lagers developed in continental Europe. While ales are brewed at room temperature, the lager is fermented at chilled temperatures. (A different strain of yeast is used, too.)

Pilsen, in what is now the Czech Republic, became a noted practitioneer of lagers, and geology again had a central role in defining the taste. The well water of Pilsen is drawn from a formation of metamorphic rocks, transformed underground by high pressure and heat so that they are almost impermeable. The water slides through cracks, but it draws almost no minerals from the rocks. This mineral-light water enhanced the clean, light taste of the beer, which became known as Pilsener.

"It came about essentially because of the geology and the waters being derived from those metamorphic rocks," Dr. Maltman said.

The pH of the Pilsen water was still in the desired range for effective mashing of the barley.

Munich, however, does not have ideal water for beer making. It is too alkaline, drawn from aquifers that lie in calcium-carbonate-rich sand and gravel washed down from the Alps. Furthermore, German law has long forbidden brewers to tweak the water chemically.