ULLAGE - The empty space at the top of a bottle, cask or barrel between the liquid and the top of the container. It is also referred to as headspace or airspace.
UNDERLETTING - Filling the space beneath the false bottom of the lauter tun with hot water before running off the sweet wort.
UNITANK - A stainless steel vessel in which the beer can be both fermented and lagered. Unitanlks have cone-shaped bottoms for allowing excess yeast to be purged out of the brew.