Over the past decade, a little-known herb 200 times sweeter than sugar has become a $4 billion global industry, showing up in everything from Coca-Cola sodas to Heinz ketchup. Not a bad start for a product that many people still think has a bitter aftertaste.

The stevia plant, which can be processed into a zero-calorie sweetener, has taken off as a sugar alternative. Consumption tripled from 2011 through 2016, according to data from researcher Euromonitor International. While it's still a small part of sweetener sales, companies such as Cargill Inc. and ED&F Man Holdings Ltd. are investing more -- including to improve the taste.

"This is a market that has huge growth potential," said Jonathan Hugh, head of the agri-industrial division at London-based commodity trader ED&F Man, which has a stake in the stevia-based Unavoo Sweetener. "We see a lot of investment opportunities."

Finding a low-calorie sugar substitute that doesn't alter the taste of iconic brands has been a longtime quest in the food industry, especially with a global obesity epidemic and rising rates of diabetes. Over the years, that's led to artificial man-made sweeteners such as aspartame, sucralose and xylitol. But many consumers report unpleasant side effects from those products, or they worry about ingesting chemical additives.

Stevia, often marketed as a natural sweetener because it is derived from plant extracts, has almost no calories and a glycemic index of zero, which means it can be consumed by diabetics.