The citric acid in your food is grown on a black mold. Pfizer figured out how to mass produce it and it's how Pfizer learned to make penicillin. Nearly all of it, about 2 million tons a year, comes from a fungus called Aspergillus niger fed sugar in steel tanks. The mold eats the sugar and gives off citric acid. The acid gets filtered off, crystallized and sold as a white powder. A Pfizer chemist named James Currie got it running at scale in 1919, and by 1939 a pound had gone from $1.25 to 20 cents. The deep tanks Pfizer built for citric acid are the ones it used for penicillin in 1941, when it was the only company making it by fermentation. About 60% of it is made in China, and the US has had tariffs on Chinese citric acid since 2009 at the request of ADM, Cargill and Tate & Lyle. Sprite, Gatorade, Hunt's tomatoes, Kraft mac and cheese, Pillsbury frosting and the liquid eggs on a hotel line all have it. It's the most used acid in food because it's cheap, it's sour, it keeps cut fruit from browning, and it holds pH where bacteria don't grow. A 2018 paper described 4 people who reported joint pain and swelling after eating foods with manufactured citric acid, but the authors wrote that nothing had been proven. No large scale controlled study has been run since.