What SRM value denotes a black beer?

The correct answer, which is an SRM value of 40, signifies a black beer due to the measurement of color intensity in the beer's appearance. The Standard Reference Method (SRM) is a scale used to quantify the color of beers, and higher SRM values indicate darker colors.

Beers with SRM values around 40 are typically categorized as very dark to black, which is common in styles such as Imperial Stouts and other similar dark ales. These styles often feature roasted malts or grains that contribute to their deep color and intense flavors.

In contrast, SRM values of 20, 15, and 30 represent progressively lighter shades, with 20 indicating darker brown or amber beers and 15 closer to a lighter brown. An SRM of 30 also signifies a deep brown but does not reach the level of black that is evident at 40. Therefore, understanding these color measurements is crucial for identifying beer styles and their characteristics.