How does botulinum toxin be produced？

how does botulinum toxin be produced？The production process of botulinum toxin is very complicated, mainly through complex technological process, to obtain high-purity toxic protein in high yield. 

Clostridium botulinum is an anaerobic bacterium that widely exists in the natural environment. In the very beginning, people find that fermented soybean products (fermented bean curd, stinky tofu, etc.) are infected with botulinum during the pretreatment, they will be fermented and preserved in the sealed anaerobic environment in the later stage.