ullage

has two primary definitions. The first refers to the free space above a liquid in a container such as a barrel, bottle, or tank. It may be intentional—to allow for expansion of a liquid, for instance—or created when a heated product cools and contracts. Ullage may also refer to the loss of liquid from evaporation or leakage (sometimes called “outages” or “angel’s share”). See angel’s share. Rates vary with humidity, heat, and barometric pressure, ranging from 2 percent to 20 percent in volume loss per year. In general, the greater the ullage, the faster the evaporation (due to the increased surface area of the liquid relative to the volume); in some hot climates where evaporation is high, cellar masters prefer to control their ullage by combining barrels once it has reached a set level.

Ullage was initially a tax concern; brewers and distillers balked at paying excise on lost alcohol. The Theory and Practice of Gauging (1740) published measurement standards for excise officers to account for ullage. Gauger’s manuals eventually included complicated equations to measure standing and reposing casks.

See also maturation.

Batemen, Joseph. The Excise Officer’s Manual and Improved Gauger. London: A. Maxwell, 1840.

Shirtcliffe, Robert. The Theory and Practice of Gauging, London: H. Woodfall, 1740.

By: Fred Minnick