The imperial stout, also known as Russian imperial stout, is the granddaddy of stouts. Typically, these intensely flavored beers are mahogany-brown to inky black (SRM 35+), very strong (7-12+% ABV), heavily hopped (50-100 IBUs), full bodied, and very complex. Common flavors and aromas include dark chocolate/cocoa, caramel/toffee, coffee/espresso, and dark fruits (e.g., plums, raisins and prunes), plus other roasty-toasty and/or burnt elements from the use of dark roasted malts. Even though hop flavors and bitterness levels can run medium to high, malt flavors usually dominate.
These beefy beers tend to be medium- to very full-bodied, with mouthfeel/textures that are often described as chewy, milkshake-like, thick, velvety and silky.
Imperial stouts are sometimes brewed with a variety of additional ingredients, including chocolate, peppers, spices, vanilla, coffee and more, and many are aged in oak barrels.
After being released in bottles, most imperial stouts continue to age really well. Aging sometimes brings out vinous and port-like qualities.
HISTORY
The “imperial” and “Russian” designations trace back to the strong English porters that were popular with the 
Russian monarchy through most of the eighteenth century. Eventually, wars interrupted the imports, and the style nearly died out. Thankfully, the style was resurrected in England and the United States during the modern craft beer revolution.
Today, English-style and American-style variations exist (American versions tend to be more roasted, bitter, and aromatically hoppy, whereas English versions tend to favor specialty malts and have more prominent yeast esters), but most interpretations fall somewhere in between the two, so they are rarely separated into two sub-styles.
BREWING AN IMPERIAL STOUT
Imperial stouts can be a challenge to brew, plus they’re expensive to make. Malt bills are massive, and they sometimes require more than twice as much malt as a “regular” stout (i.e., Irish/dry stout, for example). Additionally, high-alcohol versions must be fermented with an alcohol-tolerant yeast, and the beer needs to be fermented and conditioned much longer than typical beers.
Most beers only require a 60-minute boil, but imperial stouts are often boiled for 90 to 120 minutes or longer for a variety of reasons, but mainly to concentrate the wort through evaporation, similar to making a reduction sauce in cooking.
Oftentimes you’ll find imperial stouts with high IBUs, but it’s rare to find an overly bitter imperial stout. Heavy bitterness helps to balance out heavy sweetness.
“Brewing our Emissary Imperial Stout is a pretty awesome day,” says Wander co-owner Chad Kuehl. “Lots of barley malt needs to be milled the day before, and on the brew day our mash tun is brimming full. That coupled with the long boil time (up to 3 hours) means we only net about two-thirds the volume that we would for a normal brew.”
Emissary Imperial Stout is the second biggest beer Wander makes, after its soon-to-be-released barleywine.
LOCAL EXAMPLES
A few Bellingham breweries have released some fine imperial stouts, which is no surprise, as our local breweries tend to be rather progressive.
Kulshan’s Shuksan Russian Imperial Stout is roasty and smoky with a bold yet balanced hop bitterness. Boundary Bay’s Imperial Oatmeal Stout is rich and full-bodied with a long, roasty finish. And Wander’s smooth and delicious Emissary Imperial Stout, the brewery’s Barrel Project Release #4, was aged in 12-year Heaven Hill bourbon barrels for one year.
Other great commercial examples (that are relatively easy to find) include Avery’s The 
Czar, Great Divide’s Yeti, North Coast’s Old Rasputin, Oskar Blues’ Ten Fidy, and Sierra Nevada’s Narwhal.
