A relatively easy-to-grow herb, it’s native to South America, and is sometimes called candyleaf or sugarleaf. It doesn’t contain sugar, but the leaves are incredibly sweet anyway, and calorie-free. Sounds too good to be true, right? Well, um, it is. Because it sort of tastes lousy.

Stevia has been made into calorie-free sweeteners, some of which are white powders like sugar, for years now. But they haven’t made that much of a dent in the empire of Sweet ‘N Low and other artificial sweeteners, in large part because of the flavor. Stevia is incredibly sweet, yes—by some scales, as much as 100 times sweeter than sugar—but it comes with a strange, metallic aftertaste. Stevia doesn’t just taste “sweet.” It has a flavor, and that flavor is not widely beloved.

But researchers at Washington University in St. Louis have figured out exactly where and how the sweetness in stevia arises. They constructed, for the first time, a full three-dimensional map of the proteins in stevia, showing how the crystalline structures of the sweet parts of stevia are built. Even more importantly, they’ve mapped the chemical structures that not only produce the sensation of sweetness, but that aftertaste as well.

“One could use the snapshot of the protein that makes RebA [the major ingredient in stevia sweeteners] to guide protein engineering efforts to tailor the types and/or pattern of sugars in the stevias,” says Joseph Jez, the lead author on the study. In other words: this is the beginnings of a road map to genetically engineering a version of stevia with the sweetness but not the aftertaste.

Jez calls the version of stevia available now “Stevia 1.0.” He thinks that, with greater understanding of the chemicals within the stevia leaf and how they react to human tastebuds, we could come up with Stevia 2.0: sweet, and no aftertaste. The possibility of a plant-based, inexpensive, zero-calorie sweetener obviously has massive industry and public health implications—provided it tastes good.