Note: in the current (2015) BJCP Style Guidelines, American Pale Ale is in category 18B. Category 18 Pale American Ale contains modern American ales of average strength and light color that are moderately malty to moderately bitter.
American pale ales, at least originally, were based on English pale ales. The American style evolved alongside of the evolution of microbreweries in the United States. These beers in general would have died out completely in the U.S. market if not for America's microbrewery movement in the 1980s. Wanting more flavor in their beer drinking experience, craft brewers seized the pale ale style as their own right from the beginning of the craft beer movement. They did more than just imitate the British pale ales, they used local ingredients and made the beer their own. The American version, compared to the English version, embraces the American hop character. Citrusy and piney flavors abound. The beer is built on a base of firm bitterness with a wonderful floral aroma. Cascade is definitely the most popular hop used, but others are used as well. These hop choices are often called the "four C's". They include Cascade, Centennial, Chinook, and Columbus. All of these hops produce beers with an intense American hop character with the characteristic resiny, citrus-like flavor and aroma that many liken to grapefruit. American-style pale ales have medium body with a low to medium maltiness that may include a low caramel malt character.
In fact, Cascade is so popular that, commercially at least, a beer may not be considered "to style" without it. These beers are now a staple for most microbreweries and brewpubs.
The most important factor in brewing a great APA is the balance. You have to find the right balance between the hop bitterness and the malty sweetness, and between the toasty or bready notes and the citrus and floral notes. Watch the IBUs in your beer so the bitterness is strong but not harsh. Use lots of fresh hops in the late additions, and find a nice neutral ale yeast to keep the beer from seeming too much like an English bitter.
References: Information for this page was adapted from the 2008 and 2015 BJCP Style Guidelines, Brewing Classic Styles, 80 Winning Recipes Anyone Can Brew, by Jamil Zainasheff and John J. Palmer, and the page entitled American Pale Ale in the Beer Information/Education section of beertown.org.
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