Which of the following is NOT a sub-style of a stout?

The identification of "Scottish" as not being a sub-style of stout is based on the classification of beer styles. Stouts are traditionally categorized into various sub-styles that include Irish, Imperial, and Oatmeal.

Irish stouts, characterized by their dark color and roasted flavors, are perhaps best known through the iconic Guinness. Imperial stouts are recognized for their higher alcohol content and robust flavor profile, often with rich, complex characteristics derived from higher malt usage and sometimes barrel aging. Oatmeal stouts incorporate oats into the brewing process, which contributes to a smoother, creamier mouthfeel.

In contrast, Scottish style beers fall more within the category of ales. They are typically characterized by their malt-forward profiles and are classified separately from stouts and porters. Scottish ales vary in strength and typically feature a lighter color than stouts, emphasizing sweetness and maltiness rather than the roasted characteristics that define stouts. This clear distinction marks "Scottish" as not being a sub-style of stout.