Nature, famously, abhors a vacuum. But some cooks have learned to feel differently. Step through the swinging doors at the back of a top restaurant like Alinea in Chicago, and you may find vacuum pumps being used to reduce cooking juices into concentrated sauces, to distill essential oils from fruits and vegetables, to dehydrate chips or to brew coffee.

Many of these techniques originated in chemistry laboratories or industrial food-processing operations, and the equipment involved still evokes the bench sci­entist more than the top chef. But with all those Erlenmeyer flasks, innovative cooks have discovered ways to achieve culinary feats that are impractical by any conventional means.

Consider the common problem of concentrating the flavors and aromas that are in a dilute liquid mixture, such as a broth. The old-fashioned method—a long stovetop simmer to boil off the water—allows many of the most piquant and fragrant compounds to escape with the steam. The kitchen may smell great—but at the cost of a duller sauce. A lengthy sit over the heat also chemically alters many of those compounds that remain, so they no longer taste or smell fresh. A vacuum-reduction setup does a better job because it uses low pressure, rather than high heat, to accelerate evaporation. Pour the liquid into a Pyrex flask that has a side port and connect the flask to a vacuum pump with a rubber hose. Then drop in a magnetic rod, stopper the flask and put it on a hot plate, which uses a spinning magnet to stir and gently warm the broth while the pump reduces the air pressure inside the flask. As the pressure drops, the boiling point of the liquid falls as well; the goal is to sustain a mild, low-temperature boil.

That relatively simple setup greatly reduces chem­ical changes, but it still permits some aromatics to escape through the hose. A more expensive and complex bit of gear, called a rotary evaporator, can capture those vaporized essences and condense them back into liquid form. The cooks at our research kitchen in Bellevue, Wash., use this technique to concentrate apple juice, cabbage juice and vinegar to make a fantastic red coleslaw. Concentrated watermelon juice is also a delight.

5 Comments

1. 1. candide 11:34 AM 9/4/11

   "A lengthy sit over the heat also chemically alters many of those compounds that remain, so they no longer taste or smell fresh. A vacuum-reduction setup does a better job because it uses low pressure, rather than high heat, to accelerate evaporation."
   
   Sometimes the "alteration of compounds" is exactly what the cook wants in a long simmering process.
   
   Vacuum pumps may have their place - but one cannot simply say that vacuum pumps do a better job across the board.

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2. 2. jsfike 01:12 AM 9/5/11

   But yes, candide, one can simply say "Vacuum pumps do a better job across the board." Go ahead... try it; I'm certain you can do it.
   For the record though, the article never said "vacuum pumps do a better job across the board."

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3. 3. candide in reply to jsfike 08:26 AM 9/5/11

   "A vacuum-reduction setup does a better job because it uses low pressure, rather than high heat, to accelerate evaporation."
   
   Not the words I used, but exactly the sentiment.

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4. 4. jaythakar 08:57 PM 9/6/11

   How about using a LYOPHILIZER that will keep the food cool and concentrate. May be by making the kitchen like a lab at NIH we can stimulate US economy and create more jobs!

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5. 5. candide in reply to jaythakar 08:26 AM 9/7/11

   Why don't we just re-purpose NASA and have them produce Astronaut meals for everyone?
   
   Hey, let's keep that going - let's shrink an entire meal down to a pill...
   
   /sarcasm

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