THEY ARE one of the nation’s favourite biscuits, but have you ever wondered why chocolate bourbons have those characteristic holes in them?

It turns out there is a vital reason why these snacks and many others have holes in them, and why biscuits like ginger nuts don’t.

2 The holes in chocolate bourbons aren't just for decoration, and there is a vital reason why they feature on the popular biscuit Credit: Alamy

According to Mark Greenwell, the team manager at the pladis factory in Carlisle, which makes McVitie's and Carr's water biscuits, the holes serve a purpose in their texture.

Mark said that the holes in the soft biscuits allow steam to escape, and this prevents them from breaking or cracking.

He told host Kate Quilton on Food Unwrapped on Channel 4: “If the holes weren't there, steam would build up inside the biscuits. The biscuit would collapse back down and you wouldn't have a controllable product.

“You're trying to get steam out of the biscuits to have an even texture.”

2 Ginger nut biscuits don't have any holes, on the other hand, as they are designed to have a 'snap' when you bend them Credit: Alamy

This explanation also explains why other biscuits, such as ginger nuts, don’t have holes.

Ginger nut biscuits are designed to have a “snap”, unlike bourbons, so steam is prevented from escaping from the biscuit.

Host Kate explained: “Because the steam stays inside the biscuits, the trapped heat caramelises the sugar.

“The sugar becomes a glass like structure, like you find in a boiled sweet, and that's what gives a ginger nut its characteristic snap.”

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