Lambic beer is a unique, archaic form of beer that is quite different than modern, commonplace ales and lagers. Authentic lambics are only produced in the Senne River Valley region of Belgium near Brussels. They are unusual because, like beers brewed in ancient times, they are spontaneously fermented with wild, naturally occurring yeast and bacteria. The yeast and bacteria reside in the air as well as in brewery equipment and entire brewery structures such as decrepit roofs. The specific, ideal microbial profile that exist in the Senne Valley enables the creation of true lambic beer that cannot be reproduced elsewhere. The brewery equipment that harbors and nurtures various kinds of yeast and bacteria is never fully cleaned and sanitized. The decaying, seasoned structures of breweries are maintained as such so that important microbial flora are not lost. This is in sharp contrast to modern ale and lager breweries that use pure, laboratory-raised strains of brewing yeast and constantly work to ensure that the beer is not contaminated with microbes other than their pure strain of brewing yeast. Brown, oxidized hops that have been aged for three or more years are also used to make lambics. Unlike the green, unoxidized hops that are used to make conventional beer, the oxidized hops do not contribute much or any bitterness or hop character. They are used primarily for their natural preservative properties. The wild, unconventional nature of lambic beer makes for a complex beverage that is best experienced when served at the appropriate temperature and in suitable glassware.