tempering-vat

from The Century Dictionary.

• noun A tank for holding milk or cream while it is being tempered to bring it to the right temperature for churning or other treatment: used in creameries. It consists of two tanks, one within the other, the outer containing water which is heated by steam-pipes or cooled by ice and the inner holding the milk or cream. It is provided with thermometers for indicating temperatures in both tanks, and with gages, draining- and emptying-cocks, etc.