London (CNN) -- Coca-Cola -- the world's ubiquitous brown fizzy drink -- is staying afloat as the soda market shrinks, and many point to a marketing strategy around the so-called "secret recipe" as key to its resilience in a struggling industry.
The Coca-Cola Company, which published its full year result Tuesday, recorded a 5% drop in net income to $8.6 billion last year, down from $9 billion in 2012, as it faced "ongoing global macroeconomic challenges," according to its chief executive Muhtar Kent.
Volume grew 2% for the year, which it said was "below our expectations and long-term growth target," with sparkling beverages recording a slight increase of 1% -- led by Coca-Cola.
Globally, soda drink sales have been shrinking as consumers turn to water, fruit drinks and healthier alternatives. The trend has hit Coke and other market players such as PepsiCo and Dr. Pepper. And while its primary competitor, PepsiCo, depends on its snack business to buoy the declining soda sales, Coke announced further investment into its marketing.
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In a tough market, one strategy that brand experts credit Coke's relative strength with is the mystery around the much-hyped "secret recipe."
"The very idea of mystery attracts attention, and is often seen as an element of quality," says social psychologist and marketing expert Ben Voyer, lecturer at London School of Economics and ESCP Europe Business School. "A typical consumer would think that it must be a valuable product if they are doing all these things to protect the recipe."
Coca-Cola's "secret recipe" story -- on which it has centered advertising campaigns and built into its corporate museum --- reaches back nearly a century. According to the multi-national's website, the original recipe was only written down in 1919, more than half a century after a reported morphine addict and pharmacist John Pemberton invented the drink in 1886. Until then, it was passed down by word of mouth.
The formula was finally committed to paper when a group of investors led by Ernest Woodruff took out a loan to purchase the company in 1919. "As collateral, he provided a written record of the Coca Cola secret formula," Coke said in a statement on its site.
Since the 1920s, the document sat locked in a bank in Atlanta, until Coca-Cola decided to emphasize the secret in its marketing strategy. 86 years later, Coca-Cola moved the recipe into a purpose-built vault within the World of Coca-Cola, the company's museum in Atlanta. The ambiance is made complete by red lighting and fake smoke.
Coca-Cola has always claimed only two senior executives know the formula at any given time, although they have never revealed names or positions. But according to an advertising campaign based around the recipe, they can't travel on the same plane.
The vault, like one straight from a film, has a palm scanner, a numerical code pad and massive steel door.