What is a Imperial IPA?
Imperial IPA or Double IPA is a strongly hopped strong pale ale. Its appearance is golden to light orange-copper, with almost no hazyness. Aromas are predominantly hoppy, with notes of American hops—pine, citrus, tropical fruits, etc.—, and additional dry hopping may give some herbal character. Flavour is highly bitter, very hoppy, with floral hints from the American hop varieties. Finish is dry to medium-dry and medium to high carbonation. It's bitter and hoppier than a English IPA or an American IPA, and less malty and less alcoholic than an American Barleywine.
Imperial IPA, also known as Double IPA is a style born in the US around the late 1990's. Vinnie Cilurzo from Blind Pig Brewery is considered to be the pioneer of this style, followed by Rogue and Stone Brewing. One of the most famous and innovative examples was the 90 Minute IPA by Dogfish Head. The style was first considered as a proper category in the Great American Beer Festival in 2003.