Black Malt, or “black patent malt” as it used to be known, is a grist component used purely for color, flavor, and aroma. It contains almost no extract in terms of fermentability, and it is devoid of any enzymic activity. Colored malts generally are heated to high temperatures while the grain is still moist, but in highly colored grains, such as black and chocolate malts, the temperature in the roasting drums is up to 230°C (446°F), a temperature high enough to denature all enzymes. With a moisture content of 3.5%, and a color of over 1300° EBC (500–600° ASBC), black malt would typically be used at rates of around 3% to 5% in a grist.
Historically, black malt was a key ingredient of early 19th-century porter beers, into which it probably imparted a somewhat astringent taste, and, perhaps a smoky aroma. The invention of the process for making black malt is credited to Daniel Wheeler, who produced it using his new drum roaster in 1817. At the beginning of the 19th century, London porter brewers were restricted to using brownish malts for coloring their beers, and they would (often illegally) use various colorants for increasing beer color. Using a modified coffee roaster, Wheeler invented a method (which he patented, hence “patent” malt) for roasting malt at an elevated temperature without charring. The result gave “extractive matter of a deep brown color, readily soluble in hot or cold water … A small quantity of which will suffice for the purpose of colouring beer or porter.” The huge Whitbread brewery in London was the first to take this new product on board in 1817, and other large brewers soon followed. This development was a large and lasting change in the flavor of modern dark beers.