Stout & Porter
Roasted barley. The nitrogen cascade. Imperial Stout aged in bourbon barrels. The dark ale family from 18th-century London to 21st-century craft brewing.
Stout and Porter are dark ales brewed with roasted malts or roasted unmalted barley, producing beers with black, dark brown, or opaque appearance and characteristic roasted, coffee, chocolate, and dark fruit aromas and flavours. Porter is the older category — originating in London in the early 18th century from a blend of brown ale, pale ale, and old ale. Stout historically meant a "stout Porter" (a stronger, heavier Porter) and was used interchangeably; the term "Stout" later became independent as Dry/Irish Stout (Guinness's style), Oatmeal Stout, Milk/Sweet Stout, Foreign Extra Stout, Imperial Stout, and American Stout became distinct subcategories. The key distinction from Pale Ale is the malt bill: Stout and Porter use roasted barley or roasted malt at temperatures above 200°C, producing melanoidins, polycyclic aromatic compounds, and pyrazines responsible for coffee, chocolate, and roasted character. BJCP 2021 primary style codes: 13C (English Porter), 20A (American Porter), 15B (Irish Stout), 20B (American Stout), 20C (Imperial Stout), 13D (Foreign Extra Stout).
Guinness draught — the nitrogen system explained
The Guinness Draught system — introduced in 1959 with the development of the "Easy Serve" keg system — uses a gas blend of 75% nitrogen (N₂) and 25% carbon dioxide (CO₂) rather than the pure CO₂ used for most draft beers. Nitrogen is approximately 80 times less soluble in beer than CO₂ at serving pressure. When Guinness Draught is dispensed through a restrictor plate (a small disc with multiple small holes) at the bar tap, the turbulent flow through the restrictor forces the dissolved nitrogen out of solution as thousands of tiny bubbles, rather than the large bubbles produced by CO₂. These tiny nitrogen bubbles produce the "surge and settle" visual phenomenon (bubbles appearing to cascade downward as the denser, denser beer settles through the rising nitrogen column) and the characteristic tight, creamy head. The mouthfeel difference: nitrogen bubbles produce a smoother, creamier sensation than CO₂ bubbles because they are smaller and nitrogen does not acidify the beer as CO₂ does (CO₂ + H₂O → carbonic acid).
Porter vs Stout — documented differences
In modern usage, the distinction is primarily one of roasting intensity and body: Porter is typically less intensely roasted (using chocolate malt or brown malt rather than fully roasted barley), with more complex maltiness and lower bitterness from roasting. Stout uses roasted unmalted barley (Guinness-style Dry Stout) or highly roasted malted barley at higher concentrations — producing a more intensely dry, bitter, coffee-forward profile. The Dry Stout style (Irish Stout, BJCP 15B) is defined by the use of unmalted roasted barley — roasting without malting produces a harsher, drier roast character and less body than equivalent roasted malted barley.
Stout and Porter BJCP style specifications
| Style | IBU | SRM | ABV | Defining character |
|---|---|---|---|---|
| Brown Porter (13C) | 18–35 | 20–30 | 4.0–5.4% | Mild roast, chocolate, caramel. Moderate body. The classic London porter tradition. |
| American Porter (20A) | 25–50 | 22–40 | 6.0–12% | More aggressive than English Porter. Dark chocolate, light coffee. Higher ABV, more hop presence. |
| Dry Stout / Irish Stout (15B) | 30–45 | 25–40 | 4.0–5.0% | Unmalted roasted barley → very dry, bitter coffee finish. Low body, creamy nitrogen head (Guinness). Highly drinkable. |
| Foreign Extra Stout (16D) | 50–70 | 30–40 | 6.3–8.0% | Higher ABV version of Dry Stout developed for tropical export markets. Complex, rich. |
| American Stout (20B) | 35–75 | 30–40 | 6.0–8.9% | Bigger than Irish Stout. American hops add brightness. Rich chocolate, coffee, roast. |
| Imperial Stout (20C) | 50–90 | 30–40 | 8.0–12%+ | Very high ABV, very rich. Complex dark fruit, chocolate, roasted malt, often aged in bourbon/whisky barrels. Barrel-aged versions: vanilla, coconut, tannic oak character added. |
Maillard reactions and pyrazines — the chemistry of roasted malt
The characteristic flavour of Stout and Porter comes from Maillard reaction products formed during the high-temperature roasting of malt (or unmalted barley) above 150–200°C. The Maillard reaction — between reducing sugars and amino acids — produces hundreds of compounds including melanoidins (brown polymeric colour compounds), pyrazines (roasted, nutty, coffee-like aroma), furans (caramel), and imidazoles. The specific pyrazine compounds most relevant to roasted malt in beer include methylpyrazine (roasted, nutty), 2,3-dimethylpyrazine (earthy, cocoa), and furfural-related compounds (bread, almond). The degree of roasting determines the predominant compound profile: lighter roast (Chocolate Malt, ~200°C) = chocolate and coffee notes; extreme roast (Black Patent Malt, ~220°C+) = very harsh, dry, acidic, coffee/espresso. The choice between roasted malted barley and roasted unmalted barley (as Guinness uses) affects the β-glucan content — unmalted barley has higher β-glucan, contributing slightly more body but also producing haze. Source: Briggs, Boulton, Brookes & Stevens (2004) Brewing Science and Practice.