Visit the American Homebrewers Association for example recipes in the style.
Overall Impression: An intensely-flavored, big, dark ale with a wide range of flavor balances and regional interpretations. Roasty-burnt malt with deep dark or dried fruit flavors, and a warming, bittersweet finish. Despite the intense flavors, the components need to meld together to create a complex, harmonious beer, not a hot mess.
Aroma: Rich and complex, with variable amounts of roasted grains, maltiness, fruity esters, hops, and alcohol. The roasted malt character can take on coffee, dark chocolate, or slightly burnt tones and can be light to moderately strong. The malt aroma can be subtle to rich and barleywine-like. May optionally show a slight specialty malt character (e.g., caramel), but this should only add complexity and not dominate. Fruity esters may be low to moderately strong, and may take on a complex, dark fruit (e.g., plums, prunes, raisins) character. Hop aroma can be very low to quite aggressive, and may contain any hop variety. An alcohol character may be present, but shouldn’t be sharp, hot, or solventy. Aged versions may have a slight vinous or port-like quality, but shouldn’t be sour. The balance can vary with any of the aroma elements taking center stage. Not all possible aromas described need be present; many interpretations are possible. Aging affects the intensity, balance and smoothness of aromatics.
Appearance: Color may range from very dark reddish-brown to jet black. Opaque. Deep tan to dark brown head. Generally has a well-formed head, although head retention may be low to moderate. High alcohol and viscosity may be visible in “legs” when beer is swirled in a glass.
Flavor: Rich, deep, complex and frequently quite intense, with variable amounts of roasted malt/grains, maltiness, fruity esters, hop bitterness and flavor, and alcohol. Medium to aggressively high bitterness. Medium-low to high hop flavor (any variety). Moderate to aggressively high roasted malt/grain flavors can suggest bittersweet or unsweetened chocolate, cocoa, and/or strong coffee. A slightly burnt grain, burnt currant or tarry character may be evident. Fruity esters may be low to intense, and can take on a dark fruit character (raisins, plums, or prunes). Malt backbone can be balanced and supportive to rich and barleywine-like, and may optionally show some supporting caramel, bready or toasty flavors. The palate and finish can vary from relatively dry to moderately sweet, usually with some lingering roastiness, hop bitterness and warming character. The balance and intensity of flavors can be affected by aging, with some flavors becoming more subdued over time and some aged, vinous or port-like qualities developing.
Mouthfeel: Full to very full-bodied and chewy, with a velvety, luscious texture (although the body may decline with long conditioning). Gentle smooth warmth from alcohol should be present and noticeable, but not a primary characteristic; in well-conditioned versions, the alcohol can be deceptive. Should not be syrupy or under-attenuated. Carbonation may be low to moderate, depending on age and conditioning.
Comments: Traditionally an English style, but it is currently much more popular and widely available in America where it is a craft beer favorite, not a curiosity. Variations exist, with English and American interpretations (predictably, the American versions have more bitterness, roasted character, and finishing hops, while the English varieties reflect a more complex specialty malt character and a more forward ester profile). Not all Imperial Stouts have a clearly ‘English’ or ‘American’ character; anything in between the two variants are allowable as well, which is why it is counter-productive to designate a sub-type when entering a competition. The wide range of allowable characteristics allow for maximum brewer creativity. Judges must be aware of the broad range of the style, and not try to judge all examples as clones of a specific commercial beer.
History: A style with a long, although not necessarily continuous, heritage. Traces roots to strong English porters brewed for export in the 1700s, and said to have been popular with the Russian Imperial Court. After the Napoleonic wars interrupted trade, these beers were increasingly sold in England. The style eventually all but died out, until being popularly embraced in the modern craft beer era, both in England as a revival and in the United States as a reinterpretation or re-imagination by extending the style with American characteristics.
Characteristic Ingredients: Well-modified pale malt, with generous quantities of roasted malts and/or grain. May have a complex grain bill using virtually any variety of malt. Any type of hops may be used. American or English ale yeast.
Style Comparison: Like a black barleywine with every dimension of flavor coming into play. More complex, with a broader range of possible flavors than lower-gravity stouts.
Vital Statistics: OG: 1.075 – 1.115
IBUs: 50 – 90 FG: 1.018 – 1.030
SRM: 30 – 40 ABV: 8.0 – 12.0%
Commercial Examples: American –Bell’s Expedition Stout, Cigar City Marshal Zhukov’s Imperial Stout, Great Divide Yeti Imperial Stout, North Coast Old Rasputin Imperial Stout, Sierra Nevada Narwhal Imperial Stout;
English – Courage Imperial Russian Stout, Le Coq Imperial Extra Double Stout, Samuel Smith Imperial Stout