Imperial stout is a strong and opaque dark beer that was first brewed in London, but which is mostly associated with Russia, Baltic countries, and recently with the United States. Modern imperial stouts will typically range from deep red to dark brown.
They are full-bodied, rich, complex, and intense with typical flavors of roasted malt, dark and dried fruit, chocolate, and coffee. Most varieties will be high in alcohol, typically between 8 to 12% ABV, and they will mostly be high in hops and bitter hop flavors.
The most common legend claims that when the first batches were sent, it was noticed that stouts could not withstand the journey, and they would go bad before reaching Russia. To preserve the beer, the brewers added more hops and increased alcohol content—eventually creating a new style that will be classified as the imperial stout.
Despite this popular legend, it is more likely that the beer was intentionally tweaked to make it richer and more suitable for the Russian royals. It has been largely accepted that the model for what would later become imperial stout has been first introduced by the London-based brewery Barclay, Perkins & Co. (formerly Thrale’s Anchor Brewery).