Stevia is a sweetener and sugar substitute extracted from the leaves of the plant species Stevia rebaudiana. The active compounds of stevia are steviol glycosides (mainly stevioside and rebaudioside), which have up to 150 times the sweetness of sugar, are heat-stable, pH-stable, and not fermentable. Stevia's taste has a slower onset and longer duration than that of sugar, and some of its extracts may have a bitter or licorice-like aftertaste at high concentrations. The legal status of stevia as a food additive or dietary supplement varies from country to country. In the United States, high-purity stevia glycoside extracts are generally recognized as safe (GRAS) and allowed as ingredients in food products, but stevia leaf and crude extracts do not have GRAS or Food and Drug Administration (FDA) approval for use in food. The European Union approved stevia additives in 2011, and in Japan, stevia has been widely used as a sweetener for decades.