A Compendium of Useful Information for the Practical Man/Citric Acid

How is Citric Acid Made?
Citric acid is made on a large scale from the juice of the lime and the lemon, chiefly in the months of November and December. The juice is fermented for some time, to free it from mucilage; then boiled, filtered, and neutralized with powdered chalk and a little milk of lime. The precipitate of calcium citrate so obtained is decomposed with dilute sulphuric acid; and the resulting solution of citric acid is separated by filtration, evaporated to remove calcium sulphate, and then concentrated in vacuum pans.

The Technical world, Volume 2 By American School (Chicago, Ill.), Armour Institute of Technology