Who doesn’t love ice cream?
Especially when the sun is shining! But what is the science that lies behind ice cream making? Have a look at this graphic which takes a look at some of the
ingredients that go into ice cream, and the important role they play in
creating the finished product.
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| Graphic: Compound Interest |
Before the development of modern
refrigeration, ice cream was a luxury reserved for special occasions. Making it
was quite laborious; ice was cut from lakes and ponds during the winter and
stored in holes in the ground, or in wood-frame or brick ice houses, insulated
by straw. Many farmers and plantation owners, including U.S. Presidents George
Washington and Thomas Jefferson, cut and stored ice in the winter for use in
the summer. Frederic Tudor of Boston turned ice harvesting and shipping into a
big business, cutting ice in New England and shipping it around the world.
Ice cream was made by hand in a
large bowl placed inside a tub filled with ice and salt. This was called the
pot-freezer method. French confectioners refined the pot-freezer method, making
ice cream in a sorbetière (a covered pail with a handle attached to the lid).
In the pot-freezer method, the temperature of the ingredients is reduced by the
mixture of crushed ice and salt. The salt water is cooled by the ice, and the
action of the salt on the ice causes it to (partially) melt, absorbing latent
heat and bringing the mixture below the freezing point of pure water. The
immersed container can also make better thermal contact with the salty water
and ice mixture than it could with ice alone.
The hand-cranked churn, which
also uses ice and salt for cooling, replaced the pot-freezer method. The exact
origin of the hand-cranked freezer is unknown, but the first U.S. patent for
one was #3254 issued to Nancy Johnson on 9 September 1843. The hand-cranked
churn produced smoother ice cream than the pot freezer and did it quicker. Many
inventors patented improvements on Johnson's design.
In Europe and early America, ice
cream was made and sold by small businesses, mostly confectioners and caterers.
Jacob Fussell of Baltimore, Maryland was the first to manufacture ice cream on
a large scale. Fussell bought fresh dairy products from farmers in York County,
Pennsylvania, and sold them in Baltimore. An unstable demand for his dairy
products often left him with a surplus of cream, which he made into ice cream.
He built his first ice cream factory in Seven Valleys, Pennsylvania, in 1851.
Two years later, he moved his factory to Baltimore. Later, he opened factories
in several other cities and taught the business to others, who operated their
own plants. Mass production reduced the cost of ice cream and added to its
popularity.
The development of industrial
refrigeration by German engineer Carl von Linde during the 1870s eliminated the
need to cut and store natural ice, and, when the continuous-process freezer was
perfected in 1926, commercial mass production of ice cream and the birth of the
modern ice cream industry was underway.
In modern times, a common method
for producing ice cream at home is to use an ice cream maker, an electrical
device that churns the ice cream mixture while cooled inside a household
freezer. Some more expensive models have an inbuilt freezing element. A newer method
is to add liquid nitrogen to the mixture while stirring it using a spoon or
spatula for a few seconds; a similar technique, advocated by Heston Blumenthal
as ideal for home cooks, is to add dry ice to the mixture while stirring for a
few minutes. Some ice cream recipes call for making a custard, folding in
whipped cream, and immediately freezing the mixture. Another method is to use a
pre-frozen solution of salt and water, which gradually melts as the ice cream
freezes.
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