Food Unwrapped

Stout, Watercress, Mustard (4x6)

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Jimmy wants to know what gives stout its smooth texture. In Dublin he learns that the key ingredient is nitrogen. But how does a gas make something creamy? Kate's on the trail of the ultimate superfood. We all want to make healthy choices but when it comes to fruit and veg, do we really know what's pick of the bunch? One of these nutritional stars is watercress. But why don't we know much about it? And why is English mustard hot while the Dijon variety is relatively cool? Matt visits a leading factory to find out how they're made.