Hindustan Times: Physicist Nicholas Kurti was at the forefront of molecular gastronomy—using science in cooking during the 1960s and 1970s.
In the 1960s Kurti used to wow crowds by demonstrating the then unfamiliar technology of microwaves. Microwaves are good for heating water but not for melting ice.
A hollowed out block of ice filled with water and heated for 30 seconds in an microwave oven would result in boiling water but the ice would remain frozen. (Editor's note: Do not try this experiment without supervision.)
A microwave oven produces an electric field that reverses direction billions of times a second, forcing the water molecules to keep realigning their orientation. As the molecules realign, they collide and that collision produces heat.
But frozen water molecules (the ones in ice) are trapped in a rigid lattice work so they can't flip back and forth and create heat. That's why the ice did not melt even when the water boiled. (Eventually of course, the heat from the water would have melted the ice.)
Kurti used that principle to create a dessert called Frozen Florida with a cold exterior and a hot interior (two
recipes can be found at the link "Continue reading Making a scientific dessert".)
Related Physics Today articles
The virtual cook: Modeling heat transfer in the kitchen November 1999
Obituary: Nicholas Kurti June 1999
Some Frozen Florida recipes
Both recipes call for a hollow case made out of meringue.
In one version, the case is filled with an liqueur and put in the freezer. After a couple of hours, the case is taken from the freezer and put into a microwave oven.
In another version, the case is filled with a combination of jam, sugar, and brandy, and then capped with a meringue lid. The case is coated with chocolate icing and placed in the freezer for a couple of hours.
"Heat in microwave for only 8–15 seconds, depending on the power of the microwave.
The result is a dessert that is hot inside, but remains cold on the outside.
Almost correct, but not quite. Collisions do produce heat and can and do occur, but that is commonly caused by the motion of ions in the electric field which collide with unionized water molecules. However, dipolar rotation of water is the more common heating mechanism and results from the gain in potential energy by the molecules as they attempt to align with the rapidly alternating field. When the field relaxes, prior to changing polarity, the excess potential energy is released as random kinetic energy = heat. What is interesting about this is that as the water becomes hotter its vibrational frequency keeps getting further from the EM frequency, so the water heats at a slower rate as it gets hotter. Try heating 3 - 500 ml samples of water with starting temperatures of 10, 20, 30 degrees C and measure the temperature rise. The coldest water heats the most.
On the other hand, the presence of ions such as sodium chloride can cause the heating rate to increase as the temperature increases - a phenomenon known as "thermal runaway" that is very difficult to control.
Finally, on the dessert - that's been done for many years and there were even some supermarket products such as hot fudge sunday that were microwaved - but often failed.