Gregg Wallace explores a North Yorkshire factory that produces 625,000 sausages a day. He dons stainless steel armour to join 28 Durham butchers who prepare 2,500 pork shoulders each day and follows 20 tonnes of pork as it arrives at the sausage factory. It's a short recipe - these 97% pork premium bangers require only pork shoulder meat and seasoning. He mixes up a 150 kg batch of minced meat, loads 280 metres of skin and feeds it all into a machine which can fill 600 sausages in a minute. He also tries his hand on an old fashioned piston filler, making sausages by hand. Even the most experienced hand can only produce 1,500 sausages in an hour, while the machine filler can work 2,400% faster.

Cherry Healey is at the University of Chester getting the scientific lowdown on getting the best from your banger. It turns out that low and slow shallow frying delivers the best combination of flavour, moistness and succulence. But at a time when one in four people are reducing the amount of meat they eat, she heads to Middlesbrough to find out how veggie protein is created from a tiny speck of natural fungus. She also travels to Lincolnshire to find out how a 'meat sock' is the secret to wrapping a Scotch Egg every three seconds.

Historian Ruth Goodman finds out how German bratwurst became a top dog in America, learning how German immigrant Charles Feltman originated the hot dog. She heads to St Albans to cook up a 2,000-year-old recipe for sausages. And finally she discovers what the Romans did for Britain by importing pepper, bay leaves and other spices that spike the modern sausages.

Chocolates are an essential part of many people's festive celebrations. In this Christmas special, Gregg Wallace visits a factory which produces a staggering two million tins of festive chocolate assortments a year.

At materials intake he receives 20 tonnes of liquid chocolate at 50 degrees Celsius. This is used in 10 of the 12 sweets in the tin. Everyone has their favourite (for Gregg it's the purple-wrapped caramel-coated hazelnut) and he follows the supersized batches of the toffee, orange and strawberry varieties on their journey from tanker to tin. In just one hour 800 kilos of toffee is cut into precise 10mm x 55 mm sticks before they disappear under a chocolate waterfall. Meanwhile the orange centres make an epic 45-minute journey along 400 metres of conveyors. And 115,000 strawberry fondants head into wrapping, where 5,500 individual chocolates are packaged and dropped into tins every minute, ready to put colour into Christmas across the UK.

Meanwhile Cherry Healey is producing other festive treats. She travels to Germany - the home of so many of our Christmas traditions - where she joins a crew of 35 ornament decorators, applying glitter and paint to an army of glass Santas. In the UK, she goes behind the scenes at the Royal Mail as the Christmas stamps are printed. They'll grace the envelopes of around one billion cards this year. She also learns some tricks for perfecting gingerbread, but rather than a house, she produces a gingerbread factory complete with biscuit versions of her co-presenters. She's even got your Boxing Day leftovers sorted, bottling up 250 jars of spiced Christmas chutney.

Historian Ruth Goodman is on the trail of the Christmas turkey. It's a tradition that begins way back in the 16th century when these birds were first introduced from Mexico. But at the equivalent of £450 per bird, only the richest could afford them. It wasn't until the 1950s that selective breeding made them truly affordable for the masses. And this year we'll tuck into ten million of them. She also comes face to face with the precursor to the pantomime dame – an 18th century clown – and discovers that slapstick comedy is so-called because of a stick that was slapped together to indicate that the funny bit was coming up.