A master blender is an individual who decides on the composition of blended spirits. For example, in the Scotchwhisky industry, master blenders choose which single malts and grain whiskies are combined to make particular blended whisky. An important objective is often to maintain consistency over time. A typical blend might be composed of 20 different whiskies whose taste and price will vary over time, and, of course, it is possible that any one of them will go out of production. Consequently, it is sometimes necessary to replace whiskies that go into the blend. Other responsibilities include checking the maturation of spirits.
Master blenders very often work with one or more apprentices who will usually succeed them. Because their job is highly skilled and long term, it is common for them to work with one distiller for a long time. The longest serving master blender is David Stewart, who has worked at William Grant & Sons since 1963.