Protein bars are everywhere. Once a niche item at health food shops and sports supplement stores, they've muscled their way into mainstream supermarkets and stores, and now come in all kinds of formats and flavours.

The unusual packaging design adopted by Jacked Granny (yes, that's really the brand's name) might be seen as purely an attempt to stand out on the shelves. But it turns out there’s a practical reason why they’re using sardine tins: hermetically sealed metal containers are perfect for preserving simple ingredients without adding preservatives.

The Jacked Granny bars have just four ingredients (peanut flour, egg white, maple syrup and either dried raspberries or cocoa powder) which allows the company to achieve acceptable shelf life. The pull-tab metal tins solve a practical problem while also being easier to recycle than traditional plastic wraps.

While a tin might seem like an excessive amount of material use, it actually addresses sustainability concerns by preventing ingredients from coming into contact with air or moisture. Fewer ingredients but more packaging? Not necessarily a paradox once you consider the benefits.