Inside the Factory - Season 3

Gregg Wallace receives a load of tea leaves from Kenya and follows their journey through the factory that produces one quarter of all the tea we drink in Britain. Gregg turns his 20-tonne batch into 6.9 million bags. Along the way, he discovers that there can be up to 20 different teas in your bag and that the recipe for the blend is altered every day, measured against a standard created in 1978.

Meanwhile, Cherry Healey discovers the secrets of the tea leaf in an African tea-processing plant. She learns that 40% of each leaf is made up of chemicals called polyphenols. She is surprised to find that white, green and black tea are all made from the same leaves. She also discovers that the bag surrounding your tea is not ordinary paper, but a highly engineered fabric made up of hemp, wood and polypropylene. She watches as a 60-kilometre-long roll is produced. And she gets some scientific tips on making the best possible cup of tea with a tea bag.

Historian Ruth Goodman investigates tea adulteration. In the 19th century, there were eight separate factories in London which existed solely to dry and recolour used tea leaves. She discovers that it was 'honest' John Hornim who put that right and ensured we could trust our tea. She also finds that in the military during the Second World War, armoured divisions had to leave the safety of their tanks to brew up - a habit that resulted in many casualties. She climbs on board a modern-day tank to make a cup of tea with a boiling vessel, the innovation that solved this problem.

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.

Gregg Wallace is in London at Europe's largest biscuit factory, where they produce 80 million biscuits every day. He follows the production of chocolate digestives, from the arrival of 28 tonnes of flour right through to dispatch. Along the way, he discovers that the biscuits are shaped by a bronze roller costing up to ten thousand pounds, and that the chocolate is added to the bottom not the top of the biscuits, meaning we are all eating them the wrong way up.

Meanwhile, Cherry Healey is on the trail of that chocolate. At the refinery in Manchester, she learns that it is transported in heated lorries kept at 50C to stop it solidifying on its way to the factory. She also discovers that this is the most expensive ingredient, at around £2,000 per tonne. And she is in Nottingham University's sensory lab, where she finds scientific proof that dunking your biscuit improves its flavour and that tea is the best liquid to dunk in. Cherry takes to the streets to see if that stacks up in the real world.

Historian Ruth Goodman investigates the link between biscuits and digestion. She finds references in Samuel Pepys's diary to biscuits being a cure for flatulence and digestive discomfort and discovers that in Victorian times it was thought that biscuits could cure everything from typhoid to scarlet fever. She also takes a look at an antique biscuit baked at the beginning of the 20th century - one of Huntley and Palmer's notorious army biscuits. These dry hard biscuits were supplied as rations to five million British soldiers on the front line in the First World War.

Gregg Wallace explores the Grimsby factory that processes 165 tonnes of fish a week and produces 80,000 cod fish fingers every day. Cod arrives at the factory as compressed blocks of frozen fish. The blocks weigh exactly 7.484 kilos, which is a standardised measure in every fish factory right across the world. Gregg watches as each block is cut into 168 naked fish fingers which are then floured, battered and breaded, ready for a quick 45-second trip through the fryer. He also helps take delivery of 25 tonnes of liquid nitrogen, used to flash freeze the fingers at minus 15 degrees C. But Gregg is amazed to discover that the fish inside the finger remains frozen through every stage of production, right up to the moment you cook it at home.

Meanwhile, Cherry Healey travels to Grindavik in Iceland where they land up to 50 tonnes of cod a day. She follows the fish through the processing factory, even trying her hand at gutting the fish. Back in Grimsby, she assists with an ancient method of preserving fish - cold smoking. She learns that the yellow colour of smoked haddock is not down to the smoke but instead is produced by the addition of a natural colouring made from turmeric. Also, just like nine out of ten Brits, Cherry isn't very confident about how to safely defrost food, so she heads to the lab to get the lowdown on bacteria and freezing.

Historian Ruth Goodman is investigating the origins of cod fish fingers. She finds that Bird's Eye were the first to introduce them to the UK, basing them on a US product called fish sticks. They were introduced in 1955 and were an instant hit. 542 tonnes were sold in the first year of sale. That went up by 600% the following year. But the British public had a narrow escape - the original idea was that fish fingers would have been made with the oilier and bonier fish, herring. Ruth's also looking at Britain's original fish-based convenience food: the oyster. In the 19th century, Londoners could buy four for a penny, but an outbreak of food poisoning after a banquet in November 1902 caused a national scandal and their popularity plummeted.

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.

Gregg Wallace explores Ribena's Gloucestershire factory. It turns 90 per cent of Britain's blackcurrants into soft drinks, producing three million bottles a week. Gregg takes delivery of 500 tonnes of blackcurrants at a cider mill in Somerset. The harvest comes in during July and August, when there are no apples to process for cider, so they press blackcurrants instead. Gregg discovers how the aroma of the blackcurrants is captured separately and later added back into the drink. Next, the concentrate and aromas are transported to the drinks factory, where they are mixed with 11 other ingredients before being bottled. Gregg watches a machine that can create a plastic bottle in 0.1 of a second and learns why nitrogen is the secret to creating a bottle that won't get stuck in vending machines.

Cherry Healey is harvesting the berries on a farm in Kent - one of 40 that supply the factory. She also heads to the Netherlands to a plant that recycles plastics. It processes two and a half million used PET bottles a day, transforming them into 4mm pellets that can be turned back into drinks bottles. And Cherry is in the lab figuring out why fizzy drinks are so appealing. She learns that bubbles play sensory tricks on us, making fizzy drinks taste colder, less sweet and more flavourful than their still equivalents.

Ruth Goodman is investigating the origins of fizzy drinks. Carbonated water was first sold by Mr Schweppe in 1783, but it was a British husband-and-wife team - Robert and Mary White - who were to popularise fizzy pop. In 1890, R White's styled itself as the world's biggest drinks company and they sold 46 million bottles a year. Ruth looks at why we associate barley water with the great British summertime.