So THAT's Why Crisps Have Those Green Edges

I was about six the first time I saw a Neptune green edge on my crisps, and I quickly became convinced that was the source of penicillin. 

I don’t know where I got the idea, and I don’t believe it anymore (promise). But as an adult, I never stopped to ask myself why the verdigris verges really do appear.

Luckily, it turns out I have Channel 4′s Matt Tebbutt to do that for me. In an episode of Food Unwrapped, the presenter visited Norfolk farmer Toby Mermagen, who only grows spuds for crisps.