Manual Machines
These machines usually comprise an outer bowl and a smaller inner bowl with a hand-cranked mechanism which turns a paddle, sometimes called a dasher, to stir the mixture. The outer bowl is filled with a freezing mixture of salt and ice: the addition of salt to the ice causes freezing-point depression; as the salt melts the ice, its heat of fusion allows it to absorb heat from the ice cream mixture, freezing the ice cream.
This type of ice cream maker is inexpensive, but inconvenient and messy as the ice and salt mixture produces a lot of salty water as it melts, which the user must dispose of, and the ice and salt mixture has to be replenished to make a new batch of ice cream.
Some small manual units comprise a bowl with a capacity of about one pint (500ml) whose hollow walls are filled with a coolant. The paddle is often built into a plastic top. The mixture is poured into the frozen bowl and placed in a freezer. The paddles then are turned by hand every ten minutes or so for a few hours until the desired consistency and flavor is reached. Nancy Johnson invented the first hand-cranked model in 1843. She then sold the patent to William Young, who marketed the machine as the Johnson Patent Ice-Cream maker.
Read more about this topic: Ice Cream Maker
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