Yeast, although present in all fermented beverages, was not discovered until the 18th century. It is a member of the fungus family that, because of its cell-spliting capabilities, is self-reproducing. Yeast has a voracious appetite for sweet liquids and produces abundant quantities of alcohol (ethanol) and carbon dioxide (bubbles) as a waste product. There are limits to the amount of alcohol that certain yeast strains can tolerate without dying, hence one reason for the traditional difference in alcohol between beer and wine.
In the not so distant past, drinking warm ale in cold weather was commonplace. Because all taverns had large fireplaces, small iron pokers called “loggerheads” were hung by the fire to be used for warming drinks. In the heat of argument these pokers were often brandished by inebriated patrons giving rise to the expression “to find yourself at loggerheads.”
Until the mid 19th century all beer was made with top fermenting ale yeast which work best at warm temperatures (15 to 24°c) and produce fruity, distinctive flavours. Advances in chemistry led to the isolation and development of bottom fermenting yeast. which thrive at lower temperatures (3 to 11°c). Lower temperature fermentation takes longer and lead to the term lager, from the German word “to store.” The cleaner, more subtle, flavours associated with lager fermentation have, with rare exception, swept the global mass market.
One of the first lager beers was produced in the town of Pilzen in The Czech Republic leading to the popular style pilsner or pils.