The inorganic gaseous compound carbon dioxide has many commercial applications, including use as a carbonation agent in soft drinks, providing the signature bubbles and fizz in colas and similar beverages. Opening a can or bottle of a carbonated beverage releases pressure and allows the carbon dioxide to bubble up through the liquid.
While the term "soft drink" can mean any beverage without alcohol or dairy products, the most common usage refers to a cold, sweetened, bubble-filled beverage in a can or bottle, or obtained directly from a soda dispenser. Bottled water, coffee and tea are not considered soft drinks. The bubbles in soft drinks come from the high-pressure addition of carbon dioxide to water as the drink is being made and packaged. The fizz comes from the release of the carbon dioxide bubbles when the drink is opened or poured.
Carbon dioxide, or CO2, exists naturally in the environment and is created by the combustion process, decay, fermentation and digestion. The CO2 used commercially is primarily a byproduct of other industrial processes. According to Universal Industrial Gases, Inc., carbon dioxide for industrial use, including in soft drinks, is most commonly recovered from natural gas or coal-fueled plants making ammonia. Other sources include large fermentation operations such as breweries, and plants that make ethanol for automobile fuel or industrial uses.
The first carbonated drinks came from naturally occurring mineral springs. Ancient people believed the water had healing properties and would drink it directly from the springs. In 1772, English chemist Joseph Priestly developed a process for artificially adding bubbles to beverages. Priestly found that when he dripped sulfuric acid over chalk, it fizzed from the creation of carbon dioxide. When captured and added to water, the carbon dioxide made the water bubble.
Swedish chemist Torbern Bergman developed a system to produce carbonated water in large quantities, using the chalk and sulfuric acid method, capturing the gas and adding it to water. Another Swedish chemist, Jacob Berzelius, started flavoring carbonated water with spices and fruits in the late 1700s.
Beverage manufacturers force carbon dioxide and water into the soft drink flavoring base at pressures of up to 1,200 pounds per square inch. That pressure inside a closed can or bottle keeps the carbon dioxide dissolved in the liquid. When a container is opened, the pressure is released and the resulting energy forces the gas bubbles to rise to the surface. As all soft drink consumers know, the energy can be increased by shaking or dropping a carbonated beverage before opening the container. Over time, as the carbon dioxide dissipates, the opened beverage goes flat.
Throughout the 1800s, carbonated drinks were sold at soda fountains where the flavoring base and carbonated water were dispensed and mixed as customers ordered beverages. Baltimore machinist William Painter's 1892 invention of the crown cork bottle seal, which crimps a cork-filled metal lid onto glass bottles, allowed manufacturers to package carbonated beverages in bottles that would not explode or lose carbonation. Glass bottles were the preferred packaging for soft drinks until the second half of the 20th century, when lightweight cans gained in popularity.
Carbon dioxide can seep through plastic, which makes cans and glass bottles better containers for carbonated drinks. In plastic, the beverage loses some of its fizz over time. To compensate for the expected loss of CO2, leading manufacturers add more carbonation to beverages that are packaged in plastic.
Consumers in the United States drink about 10 million gallons of soft drinks per year. The average American consumes more than 600 12-ounce servings per year, and teenagers drink more than any other age group, according to the National Soft Drink Association.
Highly sugared soft drinks have come under scrutiny as being a major cause of obesity in the United States. The Center for Science in the Public Interest in 1998 released a report, "Liquid Candy: How Soft Drinks are Harming Americans' Health" that linked soft drink consumption with tooth decay, obesity, type-2 diabetes and heart disease. California became the first state to restrict the sale of soft drinks in schools when it banned them from elementary and middle schools in 2003. In 2005, California Governor Arnold Schwarzenegger extended that ban to high schools.