vacuum purees

trev_teich

What exactly happens when we vac a puree? Should we do it hot or cold, or dose it matter? 

Brandon_Byrd_40557

Vacuuming purees, emulsions, or other liquids will pull the air out the liquid. This decreases the overall volume of the solution and changes its texture (which no longer has pockets of air in it). It will also clarify the liquid, since the air bubbles will no longer be there to refract light and cloud the mixture. This is especially useful for solutions that have been blended since blending can incorporate a lot of small bubbles that can take a lot of time to rise out of the solution. If you're thickening a liquid with a hyrocolloid, for instance, you often disperse and hydrate the hydrocolloid powder with an immersion blender. But this introduces a lot of air, which you can then suck out using a chamber vac (if you want to).

Generally speaking, when you expose food to a vacuum it should be chilled to well below room temperature. Since the pressure at which water boils drops when pressure decreases, it's possible to boil foods at room temperature inside the vac chamber. Putting a hot (or even warm) liquid in a vacuum chamber can cause it to boil vigorously and expand to several times its volume, so if you ever do this allow enough empty room in your container for it to bubble up or else you'll have a big mess on your hands. This phenomenon can also result in undesirable changes in texture, especially with delicate items like fish (which you're not supposed to pull a hard vacuum on anyway).