On the Menu | Why making butter while you run has got social media churning with excitement

People have been storing double-bagged portions of double cream in their running vests, and somewhere between warming up and struggling through their last hundred metres, they have found they suddenly have bags full of butter and buttermilk.

This is down to the repetitive jiggling motion that agitates the cream in the bag, leading to the fat globules and liquids eventually separating.

The scientific process is known as phase inversion, in which cream (an oil-in-water emulsion) transforms into butter (a water-in-oil emulsion) as fat globules collide and coalesce to form solids.

How long this process takes depends on the temperature and how much motion you create when you run. Contrary to belief, the cream does not have to be cold to become butter. In fact, science dictates that cream at room temperature will form butter faster since the fat globules in cream can more easily move through the liquid, which becomes less viscous at higher temperatures.