Gregg Wallace is in the Netherlands at one of the world's biggest sauce factories. Its annual output is a quarter of a million tonnes of condiments, and more than 50 per cent of this heads to the UK. Our passion for sauces sees us consume 40 million kilos of mayonnaise every year. Gregg follows its production from a farm near Arnhem, where 23,000 free range hens produce the eggs, to the factory, where he is wowed by an egg cracking machine that can separate the yolks and whites from 1,700 eggs a minute. In the mayonnaise factory 'kitchen' he discovers how the delicate process of combining oil and water - known as emulsification - is performed perfectly every time on huge 480 kilo batches.

Meanwhile, Cherry Healey is making the glass jars Gregg needs for his mayonnaise. She is at a vast factory in Maastricht, where a furnace holding 250 tonnes of molten glass has been running continuously for the last 11 years. Cherry is also on the trail of another of our favourite sauces - soy - not in Japan, but south Wales, where a factory churns out bottles and sachets of organic sauce to a 2,000-year-old recipe. And the secret of its taste? A special mould called Koji.

Historian Ruth Goodman discovers how Brits fell in love with mayonnaise. She traces it back to the introduction of the bottled sauce in the 1960s and samples a series of unusual mayonnaise dishes, including the 'frosted party loaf' - a glorified club sandwich covered in mayo and cream cheese. Ruth is also on the trail of Worcestershire sauce and investigates the traditional story of its origin, as told by Mr Lea and Mr Perrins. Show less