Hand-cranked machines' ice and salt mixture must be replenished to make a new batch of ice cream. Usually, rock salt is used. The salt causes the ice to melt and lowers the temperature in the process, below fresh water freezing, but the water does not freeze due to the salt content. The sub-freezing temperature helps slowly freeze and make the ice cream.[7] Some small manual units comprise a bowl with coolant-filled hollow walls. These have a volume of approximately one pint (500 ml). The paddle is often built into a plastic top. The mixture is poured into the frozen bowl and placed in a freezer. The paddles are hand-turned every ten minutes or so for a few hours until reaching the desired consistency and flavor. Found this information for you, but @Frank Sanoica can probably explain it better.
@Hal Pollner @Bess Barber This is what happens when one superior at B.S.-ing wins others' belief in their pseudo-abilities! I will have to read Bess' description a few more times before really barging into this. As I see it: Pure water, no dissolved salts in it, including common salt (sodium chloride) and about a zillion other salts, freezes at 32` F; we all know that. Dissolving salt in it lowers that freezing point. In Chicago, we threw rock salt on our stairs to help melt the ice on them; it lowered the freezing point thus melting the ice. That implies that the temperature of ice is constant at 32`; that's not true. Ice cubes stored in your freezer at zero degrees F actually come out of there at zero degrees. Such cooled ice cubes absorb more heat from a drink, say, than would ice cubes already melting with a sheen of 32` water on them. Other end of the spectrum, it's different. You cannot heat water hotter than 212` F in an open pot; it stays at 212` until it's all boiled away, never getting any hotter than that. This is why cooking in fat is quicker, for fats boil at way higher than 212`, some as high as 400`. So, as I see it, you throw together the ingredients to make ice cream: "In its most basic form, ice cream is a mixture of cream and/or milk, sugar and sometimes eggs that is frozen while being churned to create a frozen product. In commercial ice-cream making, stabilizers, such as plant gums, are usually added and the mixture is pasteurized and homogenized." There's the kicker of the thread: CHURNED while freezing. Not sure why, except maybe to keep all the non-water-soluble stuff, fats, evenly mixed together without separating. The hand-mixer keeps churning the mix as it freezes, and to ensure < 32` F to freeze it, salty ice water is kept surrounding it, and when it finally starts to freeze-up enough, you pop the bucket of mix into your freezer, which takes it down to maybe 0` F. Note you decriers of eating uncooked eggs: ice cream contains uncooked eggs! (WHEW) Frank
How long will it take you to build one, @Frank Sanoica ? I have not the slightest doubt that a man of your genius can build a working model quickly. You can make ice cream in a plastic freezer bag. Actually, two freezer bags. Fill a smaller bag with your mix. Put it inside a larger bag. Put ice and salt in the outside bag and shake it. Shake it, Baby, shake it! Soon your mix will become delicious hand made ice cream.