The Story on Zevia
In other articles on this site, I have mentioned that natural Stevia still is not allowed to be sold in food and beverages, yet Zevia contains natural Stevia (or so they claim). How is this possible? The reason that Zevia can be sold legally - in spite of the fact that Stevia still is a forbidden food additive - is that it is not sold as a soft drink, but as a dietary supplement! Note that Zevia contains the artificial sweetener Erythritol.
After some Googling, I found out that Zevia's Stevia is produced by the Chinese company Sunwin International. They supply Stevia extract from Stevia plants grown in China. According to this source, refined Chinese Stevioside is only 80-91% pure and some samples have been found to be high in "pathogens". Of course this does not prove that Sunwin's Stevioside is in any way tainted. Literally, "pathogens" means disease-causing organisms like bacteria, virii, fungi, prions or parasites - but I assume the author means chemical pollutants like pesticides, herbicides and heavy metals, as well as residues of the chemicals used in the extraction process. If you want to know the details of Stevia cultivation and Stevioside production in China, you'd have to dish out 8000 bucks..
This Chinese article on Stevioside production in China says that most Chinese Stevia producers produce "low grade and bad quality". They mention a more modern "enzymatic modification" method, of which I found a patent. This method uses mashed Stevia leaves in water, microorganisms and Ethanol to yield a high-purity Rebaudioside A concentrate. I do not know what process SunWin uses. Meanwhile, Zevia bullies Wikipedia contributors with litigation and effectively censors Wikipedia articles about Zevia: