Gregg Wallace is in Italy, hitching a lift on a train carrying over a thousand tonnes of wheat to the largest dried pasta factory in the world. It produces 60% of all pasta made in Italy and supplies 3,000 tonnes to the UK each year. Gregg traces the journey the wheat takes through a seven-storey mill and into the production zone where it is mixed with water, pushed through moulds and turned into spaghetti. Along the way, he discovers that the perfect string of spaghetti is 25 centimetres long and examines the technology that allows them to produce 150,000 kilometres of it each day - enough to stretch round the earth almost four times.Meanwhile, Cherry Healey discovers why the best pasta is made with durum wheat. This is a hard wheat that, when it is milled, turns into the granular yellow flour known as semolina, which translates as semi-milled. This is the essential basis of pasta as it retains its shape and texture when cooked. She also helps to harvest 15 tonnes of tomatoes, turning them into 3,000 litres of pasta sauce. Along the way, Cherry is surprised to hear that the British habit of pairing spaghetti with bolognese outrages many Italians. She learns why different shapes of pasta are ideally paired with different sauces and promises in future she will serve her spaghetti with a more suitable topping, like carbonara.Historian Ruth Goodman discovers that pasta arrived in Britain much earlier than we imagined. She heads to the British Library to look at a manuscript from 1390. It is a cookbook written for King Richard II which contains a recipe for something called lozyns. Ruth cooks up a batch and is convinced that this an early version of lasagne. She also navigates the streets of Soho armed with a 1958 restaurant guide to find out how we first fell in love with Italian food.