Some sauces or sauce components are best boiled or evaporated under vacuum so that the temperature inside the vessel can remain relatively low. This way, the sauce can be reduced and its more delicate and fleeting components remain intact, since they have not been exposed to high heat. This is especially useful when working with fine wines or delicate gelées in which the finesse of the sauce is particularly important.
While there are many kinds of vacuum pumps, some costing many thousands of dollars, two types are most commonly used in the kitchen. A medical vacuum pump is relatively inexpensive, and convenient to use. Most such pumps come with a separate vessel—a trap—that can be used to condense excess water vapor and thus prevent moisture from entering the pump (which would cause damage). A trap is in essence another flask with a two-holed stopper and two lengths of glass tubing (one for each hole) that is set up between the main flask and the pump. The trap is best submerged in ice water (along with any tubing leading to it) so that it condenses any moisture before it can reach the pump.
Least expensive is a vacuum aspirator that connects to the kitchen tap. When the water is run, a vacuum is created in the side arm of the device. While these can be highly effective, they have the disadvantage of using a great deal of water.
To use a vacuum pump, set up an Erlenmeyer flask with a one-hole stopper. Insert a couple of inches of glass tubing into the hole to attach the hose. Attach about 3 feet of rubber tubing to the glass tubing in the cork, then attach the other end of this tubing to the trap. There are several ways to set up a trap (see Concentrating Coulis and Fruit Juices in a Vacuum), but one easy way is to use another Erlenmeyer the same size as the other one. Insert a two-hole stopper and connect the hose from the first flask. Attach another length of rubber tubing from the second hole in the cork to the pump.
Submerge the first flask and the first length of rubber tubing in ice water. Keep the flask from bobbing up by securing it to the bottom of the bowl. In this way, as the vapor comes off the boiling liquid, it is condensed and liquefied in the trap before making it to the pump.
Copyright © 2017 by James Peterson. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.