Conversation so far:
where does caffeine come from in energy drinks?
The majority of caffeine is now made in China with 3 Chinese factories together exporting 4 million kg of caffeine alone to the USA every year.
where in China is the majority of caffeine is made?
the majority of the world’s synthetic caffeine comes from just one Chinese town: Shijiazhung

Question: what is the largest factory?
Self-contained rewrite: what is the largest caffeine factory in China?