I heard this yonks ago but could never find the straight dope on it from google.
It seems the Pharoah in Ancient Egypt was, if anything, fonder of his ‘ice cream’ than even the Ancient Roman Emperor.
This latter could source his stuff from the Alps by runners, but ol’ Pharoah was too far away from them for that, to say nothing of the Med to cross; but his magicians discovered how to make ice by drawing air across the water surface in the water-jar fast enough so that the cooling effect of the evaporation was enough to form ice crystals.
I don’t believe this story is true as stated but they are probably referring to a variation of evaporative cooling. These are also called swamp coolers even though they only work in dry areas. The basic principle would work in a dry climate like the Egyptian desert but I don’t think it will actually create ice for ice cream. They would also need some ingenious engineering to make it work at all even as an air conditioner let alone a freezer because they didn’t have electricity or motors to produce high speed air flow over the cooling surface.
If you can somehow pump a decent vacuum, you can get water to freeze. It can be done with dessicant like zeolite (which is a naturally occurring mineral, mostly supplanted by synthetic versions today) or by mechanical pumping. I don’t think the Egyptians had access to such technology though. Basically you have to be able to build airtight plumbing and vacuum vessels that won’t collapse.
My handheld IR thermometer shows that the clear night sky in Seattle acts as a -40C blackbody. If a small amount of water could be suspended above a reflective metal plate for many hours, and if air circulation could be halted (or perform this on a very still night,) probably one could make ice via radiative cooling.
So, on clear still desert nights would we ever see bits of ice on, say, plant stems positioned above some sort of accidental IR reflector?
As pointed out above it is possible to make ice in a desert, and that would be a natural discovery, as all it takes is leaving a pot of water out exposed to the night sky.
That method was also used to increase alcohol levels in drinks. The water would freeze out of the alcohol-water solution and then the ice would be removed.
Some low carb recipes for ice cream used a artificial sweeter and alcohol, the alcohol prevented a hard freezing and a more ice cream like consistency without the stirring. This may also work with sugar ice cream.
While I don’t know of anything specific to Egypt, in the ancient world they had various different ice storage technologies that allowed people to store ice long term without it melting. The Persians are believed to have invented the first ice houses but there is archaeological evidence for independent inventions in China as well.
A properly constructed ice house can actually store ice indefinitely, through summer, without the ice melting away. An ice box as seen in the 20th century was not the same thing, and ice in those did need to be refilled continuously (thus ice delivery men existed–my grandfather actually delivered block ice to homes during his summer breaks from college.)
So if Egyptians had such buildings they could have ice long term. Now, how does the ice get to Egypt? It could have been shipped across the Mediterranean, really. You can store ice in straw-packed boxes in a ship and it won’t melt. In the early United States businessmen in New England actually ran operations that would package ice and ship it south to the southern states. Wealthy southern plantation owners would buy the ice to stock up their ice houses.
They actually did a lot better than that. Up until the invention of refrigeration, there was a thriving industry in New England that not only shipped ice to the southern states, but all the way to India via sailing ships. Made a lot of money out of it, too.