Next time you reach for a cold can of Coke, spare a thought for the millions of people who lived before fridges were invented.
Keeping food cool keeps it fresher for longer. Since food that isn’t fresh can kill you, this is very important. Before fridges, people put food in cold, dark, damp places, or in a hole packed with ice or snow. Artificial cooling started more than 250 years ago.
In 1748 William Cullen demonstrated how freezing temperatures could be obtained by evaporating ether. But he didn’t use it to build a fridge.
Oliver Evans, an American inventor, proposed a refrigeration machine in 1805 that used compressed ether, but he never developed the idea.
Jacob Perkins was the first person to actually build a machine that cooled things down. He patented his invention in 1834.
The first commercial refrigerators were used in the brewing and meatpacking industries in Australia and the USA in the 1850s. Improvements in the design led to the first domestic fridges going on sale in 1913.
Until 1929 fridges used poisonous gases ammonia, methyl chloride and sulphur dioxide, which caused several deaths. After that Freon was used, a compound invented by two scientists called Charles Franklin and Thomas Medgeley, Jr, and manufactured by Du Pont. It was much safer, but years later people realized that the chlorofluorocarbons in Freon were destroying the Earth’s ozone layer!
Relatively cold: Albert Einstein came up with all sorts of clever things. Not many people know that one of them was a fridge, which he invented in partnership with a former student, Leo Szilard. They took out a patent in 1930.
The ice-cream-making process takes a lot of time, but the results are well worth it. Ask an adult to be your assistant.
WHAT YOU NEED
a big bowl, a saucepan, wooden spoons, a fridge, a freezer
INGREDIENTS: 4 egg yolks, 1/2 pint (250 ml) milk 1/2 pint (250 ml) double cream, 4 oz (100 g) sugar or caster sugar, 2 teaspoons of vanilla extract (or more according to taste)
Put the egg yolks and the sugar into a big bowl and stir until the mixture gets thicker.
Pour the milk into a saucepan and bring it to the boil. Then add the the milk to your sugar and egg mixture, but keep stirring at all times.
When thoroughly mixed, pour the liquid back into the saucepan and heat gently, stirring all the time until the mixture thickens.
IMPORTANT – DO NOT BOIL. Once thickened, remove the saucepan from the heat and leave to cool.
The mixture you have made is the basis for all ice-cream flavors. Add the vanilla essence now if you want vanilla ice cream, but at this point you can create any flavor you like – so experiment (check out ice-cream recipes).
When your mixture is cool, you could put it into an ice-cream maker for an easy life, but if you haven’t got one, pour the mixture into a plastic food container and chill it for a few hours in the fridge. Then stir in the double cream and transfer the mixture to the freezer for half an hour. The ice cream should have started to freeze – but you don’t want it to be fully frozen as you have to beat it.
Beat the mixture until there are no lumps and it becomes liquid again, then return it to the freezer, beating it again half an hour later. Repeat this process three times and your ice cream should be ready to eat.
Here is a way to make mischief. Why not make six different ice-cream dishes and make one of them a nasty flavor? For instance, you could have five great flavors such as: chocolate, vanilla, strawberry, banana and mint choc chip, and then one really nasty flavor – like tomato ketchup or mustard flavor.
Bring your ice creams to the table when they’re ready. Serve them into identical dishes and place them on a tray. Now invite your guests in.
It’s time to spin the tray. When it stops spinning each person must take the flavor that ends up in front of them, but try to make sure you don’t get the tomato ketchup flavor! Leave that one for Dad!