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.

Gregg Wallace is in Italy, at an enormous pizza factory where they produce 400,000 frozen pizzas each day. He mixes up a 450 kilo batch of dough for the bases; enough for 180 000 pizzas. He watches as each one is stretched to exactly 26 centimetres in diameter, then pricked with 522 holes, each 4mm deep, before they're topped with tomato and disappear into the wood fired oven. It's 25 metres long and the floor is made of rotating panels of volcanic rock heated to 450 degrees Celsius. Gregg's pizzas emerge fully cooked after just 80 seconds. They're topped with cheese, pepperoni, chillies and onions, then frozen and dispatched on their 1000 mile journey to the freezer compartments of British supermarkets.

Meanwhile Cherry Healey is asking if mozzarella – the traditional choice for pizzas - is also the scientific best bet. She finds that not all cheeses are equal, and that to melt well they must sit in a pH zone between 5 and 5.9. This explains why blue cheese and feta don't work on pizza but mozzarella and gruyere do. In Austria, she transforms 400 kilos of pork into pepperoni. She learns that this preserved sausage is fermented and salted to give it a long shelf life. A production process that takes more than 2 weeks.

Historian Ruth Goodman is investigating the technology that allows frozen foods like pizza to be transported across the globe. 150 years ago we were all 'locavores', eating locally sourced food. But in the 1880s the game-changing invention of freezer ships meant that lamb and beef could be shipped from New Zealand and Australia. Combined with the 1938 arrival of the freezer truck, this created the worldwide cold chain that we rely on today. She also meets the man who popularised pizza in the UK back in 1965 when he opened his first restaurant in London's Soho.