Last year, when touring a Sears prefab house from 1925 in Sanibel, Florida, I was impressed with the Toledo cooker in the kitchen. It worked by heating up a heavy concrete disk in your stove, then dropping it into a very well insulated box. The manufacturer wrote in an ad: "Meats-even the cheapest cuts-have a new delicacy and richness, because they are cooked in their own juices....The scientifically arranged insulation prevents heat loss through compartment walls." This seemed like such a good idea, a crock pot that didn't need electricity.
Turns out, it was such a good idea that it is still being done, with a vacuum instead of the asbestos or rock wool or whatever was in the Toledo cooker, and without a concrete block; the food itself provides the thermal mass. You put in your food, set the inner unit in water and heat it to a boil. Stick it in the outer vacuum container and it will stay hot (and continue cooking) for six hours.
Rita at Cool Tools describes a bit of its history in America:
Incredibly, the first time this device was debuted in the U.S., it was marketed towards tailgaters and, well, flopped.
She thinks it was aimed at the wrong market.
The crock pot has recently come back on the market, and is again being hyped as a tailgater essential. Bah. Tailgaters and church-potluckers aren't going to shell out $179 for a crockpot. People who do endurance races in the northern climates: now there's your target audience. And don't forget that this crockpot is more electricity-efficient than the normal kitchen plug-in models; it takes none once it's hot so it makes a great kitchen addition for the average treehugger.
A wonderful idea, and another example of a lesson from the past that can be a template for the future. They sell it at Amazon.