Nisin is a natural antimicrobial agent, derived from controlled fermentation of the naturally occurring bacteria Streptococcus lactis, found in milk. It is used as a preservative in heat processed and low pH foods. Nisin cannot be artificially synthesised, so Streptococcus lactis is 'farmed' to synthesise the nisin.

Found in beer, processed cheese products and tomato paste. Basically an organic product with no known adverse effects.