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How Soda Fountains Work

Soda Fountains, Then and Now

Over the past 200 years, soda fountains have evolved from giant, room-sized machines run by teams of men to countertop devices that prepare and dispense tongue-tickling beverages in seconds.

After Jacob Schweppes invented the hand-cranked carbonator in the 1780s, the biggest technological challenge was isolating large volumes of carbon dioxide gas. A breakthrough came in 1832, when English-born inventor John Matthews patented his ingenious soda fountain system in New York City [source: Oatman-Stanford].

Matthews knew that you could produce C02 by combining sulfuric acid with pulverized marble dust, which is rich in calcium carbonate. He built a sealed cast-iron boxed lined with lead and filled it with a precise blend of acid and crushed marble. The carbon dioxide generated by the chemical reaction would rise through a water chamber for purification and into a pressurized carbonation tank containing cold spring water [source: Yates].

In the early days, subterranean workers in Matthews' New York soda fountains would manually shake the tanks of spring water for a half-hour to fully carbonate the liquid, which would then be piped to the taproom at street level above [source: Yates].

Contrast the primitive technology of those first soda fountains with the self-serve units found in most fast-food restaurants. Inside these tabletop machines, which can serve eight or more flavors of soft drink at once, is a pressurized C02 tank, a water pump and a carbonator. The C02 tank and the water pump send pressurized gas and cold water into the carbonator where the C02 dissolves completely.

When the soda dispenser tab is pressed, carbonated water is released from the carbonator. At the same time, a second pump sends a squeeze of flavored syrup from one of several name-brand bags loaded into the unit. The ratio of water to syrup is roughly five to one [source: Carbonics]. The cocktail of carbonated water and syrup is blended right at the dispenser head as the product hits the cup.

Between the creation of the technology for aerated water and the modern soda fountain, which is basically a stand in a restaurant where you serve yourself a drink, was a time when you got your soda from pharmacists who served up "medicinal" concoctions with a spoonful of sugar and lots of refreshing fizz.