In the Middle Ages and the early modern period beer was mainly drunk from stoneware jugs, which were fired at high temperatures. As a consequence the beer would not penetrate the pores of the material and cause it to molder. Until well into the 18th century beer was considered a staple food. Average daily beer consumption is thought to have been around two liters beer, but the alcohol content of the brew was low. The high beer consumption may be related to the poor quality of drinking water. Water is not safe to drink: especially in cities, it comes from wells that are often only a few meters away from abortuaries, dung heaps or tanneries. Until the 15th century people here drank a slightly carbonated beverage known as gruit ale. Its characteristic flavor came from herbs and spices such as anis, caraway and juniper, and above all the leaves of the sweet gale shrub. In the 15th century hops began to replace gruit as a flavoring additive. The new hopped beverage was top-fermented like gruit ale, and can be considered the ancestor of today’s Altbier.