I'd imagine any inventor whose creation becomes genericized, like Kleenex or Jell-O, has to be pretty proud of themselves. Such an inventor creates a product, gives it a brand name, then BAM! Everyone forgets you aren't the only one who produces that product. Your company is pretty much the king of that specific product, you would think.

Such is the case with the king of the vacuum flask. You would know the company as Thermos. Like many food-related items, when the first vacuum flask was invented in 1892 it wasn't specifically invented with food in mind. No, Sir James Dewar was working in cryogenics, not gastronomics or any other food specific science. Dewar wasn't keeping his coffee or tea hot; he was attempting to determine the specific heat of palladium.

Dewar had to create a specific chamber for his experiment and that chamber was placed inside another chamber. In the space between the two, Dewar had the air removed, hence “vacuum flask." Dewar refused to patent his invention, otherwise we might refer to them as Dewar Flasks instead of Thermos. Still, a very old and very dependable piece of gear for working folks and cooks alike.

I didn't really consider the vacuum flask's potential in the kitchen until watching the June 16, 2004, episode of "Good Eats" in which food scientist and one of my personal heroes, Alton Brown, demonstrated how a vacuum flask could be used to stabilize sauces like hollandaise, which are ruined if they get too hot or cold before being eaten and cannot be reheated.

Little did I know thermal cooking, also vacuum flask cooking, has been around for a long time. It's a cool trick where a vacuum flask is not only used to keep food hot before consumption, but is used to complete the cooking process. I cooked many, many ramen lunches this way in China.

The technique used for thermal cooking goes all the way back to the medieval period in Europe. Because of the inability to create a vacuum, the process was less efficient, but still the same concept.

In this case, one hot, earthenware pot with food was placed inside another container (pot, box or hole) and insulated with various materials. In a way, this is how the Bean Hole Days beans are cooked. Instructions still exist from an Anglo-Norman manuscript in the British Library (via Wikipedia).

“Take a small earthenware pot, with an earthenware lid which must be as wide as the pot, then take another pot of the same earthenware, with a lid like that of the first; this pot is to be deeper than the first by five fingers, and wider in circumference by three; then take pork and hens and cut into fair-sized pieces, and take fine spices and add them, and salt; take the small pot with the meat in it and place it upright in the large pot, cover it with the lid and stop it with moist clayey earth, so that nothing may escape, then take unslaked lime, and fill the larger pot with water, ensuring that no water enters the smaller pot; let it stand for the time it takes to walk between five and seven leagues and then open your pots, and you will found your food indeed cooked.”

Steel cookers were developed in Asia and even now Asian countries are perhaps most likely to utilize this incredibly cool, incredibly energy efficient cooking method. They have upgraded from vacuum flask to vacuum cooker, which they use almost like a crockpot (genericized again, see).

In the United States it can be seen more commonly as a novelty in which ears of corn are piled into a cooler, followed by kettles of boiling water and allowed to sit for 30 minutes. (If anyone knows where to get a cooler with a metal interior liner, I want one just for this.)

That being said, thermos cooking can be used to cook virtually prepackaged pasta or dry soup mixes, some dry beans, quinoa, couscous, rice, porridge, oatmeal and many other items.

Vacuum Flask Paella

  • ½ cup white rice
  • 1 cup stock (chicken or seafood) or water
  • ½ cup chopped, precooked chicken (or a can)
  • 1/3 of a single chorizo or other spiced sausage, chopped and browned
  • ¼ cup chopped onion and green pepper
  • 1 teaspoon turmeric or 3 threads saffron
  • A few cocktail shrimp (optional)
  • Splash of clam juice
  • Pinch of salt
  • 3-4 threads saffron or ½ teaspoon
  • Pinch of garlic

It is vital to ensure all ingredients are hot before going into the thermos and meats are cooked through (you can speed this up by using precooked meats). If starting raw, begin by cooking your chicken and chorizo in a pot deep enough for your rice and water. Once they are done, add your vegetable ingredients, followed by rice and seasonings. Stir this to coat with the flavorful meat juices and then add water. Bring this to a boil and allow to boil 3 minutes.

To prime or prepare your thermos, microwave or boil enough water to fill your thermos by half at least. When your food is done precooking, first place your thermos in the sink and add the hot water. Seal it and turn it to heat all the inside surfaces. Quickly open and empty this thermos, and while it is hot, use a canning funnel to add your precooked ingredients to the thermos and seal. Shake well to keep it distributed and keep it in a fairly warm environment. Some suggest keeping this on its side. Your food should be hot and ready by lunch time (about 3 hours).

Hollandaise Sauce

  • 3 egg yolks
  • 1/4 cut water
  • ¼ teaspoon salt
  • Pinch black pepper
  • 2 tablespoon lemon juice
  • ½ cup butter cut into pads

Whisk your egg yolks, water and lemon juice in a small saucepan until blended. Cook over very low heat while whisking until mixture bubbles slightly at the edges. Stir in the butter one pad at a time until melted and thickened. Remove from heat immediately and stir in salt and pepper. Serve immediately or keep hot in a vacuum flask.