Beer Planet beer category indicating highly bitter beers, i.e. being at the upper level of IBU (International Bittering Unit) scale, which is provided by the hops used during brewing. Hops contribute bitterness, flavour and aroma to a beer in different ways depending on when they are added during the brewing process. How much hop bitterness and aroma is appropriate varies considerably between different beer styles. There are many varieties of hops, some of which are associated with beers from specific regions.