快猫短视频

MOST foods are pretty challenging to eat when they are frozen, but ice cream manages to be soft and creamy when it has just come out of the freezer. It seems magical, but there are some easy ways to make delicious ice cream at home, without any special equipment.

A basic ice cream is made from cream, milk and plenty of sugar. The sugar doesn鈥檛 just provide sweetness, it lowers the freezing point of the cream. To solidify into ice, water molecules must arrange themselves into a framework. Sugar molecules are big and don鈥檛 fit into the framework very easily, so the solution needs to become much colder 鈥� slowing the molecules down 鈥� to freeze.

As a result, sweetened cream only partially freezes in the freezer. Once most of the water in the cream has formed into ice crystals, the remainder becomes so concentrated with sugar that it stays liquid in the freezer.

In fact, ice cream has three phases: solid ice crystals, liquid cream and pockets of air. It is usually made in machines that churn the cream as it freezes to get more air into the mixture, which makes the ice cream lighter and easier to scoop.

Churning also helps keep ice crystals small, key to the texture of the ice cream. If the crystals are bigger than about 50 micrometres, your tongue can sense their rough edges. The faster the mixture is frozen, the smaller the crystals and the smoother the ice cream.

鈥淣o-churn鈥� ice cream recipes can be put straight into the freezer without being mixed in a special machine. These usually mean you have to whip the cream, building air into the mixture, before other ingredients are added. The recipes often use sweetened condensed milk instead of normal milk to lower the water content relative to fat and sugar, making it harder for large ice crystals to form.

If you are using this method, fast freezing is particularly vital in keeping the ice crystals small, so make sure everything is thoroughly chilled before you start and then freeze the mixture in small, shallow containers.

Another way to make ice cream exploits how solutes lower the freezing point of water. When we scatter salt on an icy pavement, the ice melts 鈥� but it absorbs heat from its surroundings to do so. Before the advent of refrigerators, ice cream was made by putting the cream in a can surrounded by salt and ice. The salt would melt the ice and produce a supercooled brine with a temperature many degrees below 0掳C, which, in turn, would freeze the cream.

To make ice cream this way, mix the ingredients in a small, sealable bag and seal it, pushing out as much air as you can. Put this in a second such bag to ensure it doesn鈥檛 leak. Put this inside a larger sealable bag with the ice and salt. Close this, wrap it in a towel and gently squeeze or shake it until the mixture looks like ice cream, usually in about 10 minutes.

For other projects visit聽newscientist.com/maker.