In this Christmas special, Gregg Wallace, Cherry Healey and Ruth Goodman explore the fascinating factory processes and surprising history behind our favourite festive treats.

Gregg Wallace receives some tea leaves from Kenya and follows them through the factory that produces one quarter of all the tea drunk in Britain.

Gregg Wallace is at the world's largest dried pasta factory in Italy, where they produce 150,000 kilometres of spaghetti each day.

Exploring the fascinating factory processes behind Christmas cake, baubles, brandy and more. And why Christmas tree lights are called fairy lights.

Gregg Wallace explores the Grimsby factory that processes 165 tonnes of fish a week and produces 80,000 cod fish fingers every day.

Ruth Goodman investigates the origin of Worcestershire sauce, as told by Mr Lea and Mr Perrins.

Gregg Wallace explores Ribena's Gloucestershire factory. Meanwhile, Cherry Healey is in the lab figuring out why fizzy drinks are so appealing.

How Britain's biggest brewery produces 3 million pints of beer a day in Burton upon Trent. How four basic ingredients – water, malted barley, hops and yeast – are manipulated to make dark, heavy ales; light, fragrant lagers; and everything in between. How the hard water of Burton – perfect for brewing flavourful stouts and porters – and its position on the canal network made it the centre of brewing in 19th-century Britain. How beer-making turned from a predominantly female cottage industry to an industrialised process dominated by men.

How a cheese factory in Gateshead produces 3,000 tonnes of spreadable cheese every year - making cheddar, chopping and blending it with whey, water, and other ingredients. How bacteria affect the aroma, flavour and appearance of cheeses. How to make perfect cheese on toast. How cheddar became the predominant hard cheese world wide. How Kraft made processed cheese 100 years ago.

How a foundry in France produces a cast iron pot every five seconds - from the arrival of 20 tonnes of crude iron right through to brightly coloured orange casserole dishes. How a South African iron ore mine - one of the largest in the world - produces a staggering 670,000 tonnes every day. The science behind cooking the perfect casserole - more cooking time isn't always better. The history of one-pot cooking to prepare simple meals, from communal ovens to 1970s slow cookers. How casting iron in sand moulds democratised the kitchen through affordable cookware.

How a factory in Wigan produces two million tins of soup a day. Vegetable soup is followed from a pea harvest in Yorkshire right through to the finished soup going into cans and being dispatched. How the vitamin content of frozen vegetables can greatly exceed that of fresh. How a spinach soup based on a 17th-century recipe doesn't much resemble soup as we know it today. The history of the soup kitchen.

How a factory in Essex produces 400,000 cereal bars a day - from nuts to cranberries and sultanas to puffed rice, with a carefully balanced blend of honey and glucose binding it all together for the ideal texture. How macadamia nuts are harvested in South Africa, and shelled under extraordinary pressure. The scientific distinction between botanical nuts, legumes and drupes. The history of Britain's cereal bars, including one Kendal Mint Cake snack bar made popular by famous explorers Ernest Shackleton and Sir Edmund Hillary.