Gregg Wallace is in Gateshead at a cheese factory where they produce 3,000 tonnes of spreadable cheese every year. He follows the production of jalapeno chilli flavour cheese from a 28,000 litre delivery of milk to 5,400 squeezy tubes. The process begins in a traditional way – by making cheddar. He learns about the microbiology responsible for splitting milk into curds and whey and forming this hard cheese. He then chops 344 kilos of cheddar and gouda to make the base for his squeezy cheese, and puts it in a huge blender with whey, water and other ingredients in order to stabilise it and keep it soft and spreadable.

Meanwhile, Cherry Healey is finding out how bacteria are responsible for the huge variety in smell, taste and appearance of different types of cheese. She learns that some smelly cheeses contain the same bacteria that are responsible for stinky feet. In cheese the odour is a by-product, a sign that the bacteria are silently changing the internal texture and taste of the product. She also learns the scientific rules for making perfect cheese on toast. It is all about medium sliced white bread, with precisely 50g of grated medium cheddar, set an exact 18 centimetres from the grill.

Historian Ruth Goodman is finding out how cheddar, originally just one of hundreds of regional varieties in the UK, became the predominant hard cheese world wide. She discovers that it is down to a Victorian cheesemaker called Joseph Harding who first standardised production methods. She also makes a batch of processed cheese, using Kraft's original 100-year-old patent recipe.

Gregg Wallace is in Germany, at a historic factory which produces 600,000 pencils a day. At materials intake he is astonished that the main material in a pencil is not lead, but graphite. He helps mix this with clay to produce a 250-kilo batch – enough for 200,000 pencils. He also discovers why these pencils are hexagonal - because it stops them rolling off the table. And he performs an unusual quality check by throwing his finished pencils from a 25-metre-high tower. When they are chopped open the leads are still intact.

Meanwhile, Cherry Healey is at Manchester University examining the astonishing properties of graphite. She discovers that this highly conductive form of carbon is also able to withstand temperatures up to 3,000 degrees Celsius. More surprising still, if you strip a single layer of atoms from its surface, you produce an entirely new material known as graphene. Thin and virtually invisible, embedding this in our phone screens could mean that in future we could simply roll them up. She is also investigating the science behind graphology and asking if we can evaluate personality from handwriting style.

Historian Ruth Goodman is on the trail of the very earliest pencils in the Lake District. It is a story which begins in the 15th century with the discovery of a huge deposit of pure graphite in the Borrowdale valley. Carved into sticks and wrapped in string, it made a brilliant writing tool. Ruth is also wondering if, in this modern digital age, the pencil is outdated technology. But she finds documents that show the death of handwriting has been prematurely announced on many occasions, dating right back to the invention of the printing press.

Gregg Wallace is in Burton upon Trent at Britain's biggest brewery, where they produce 3 million pints of beer a day. He follows the production of Britain's best-selling lager from raw barley to finished cans. Along the way he gets to grips with brewing terms like mash, wort, grist and coppers, and learns how 0.2 millilitres of yeast is enough to make 1.3 million pints alcoholic. In this high-volume factory he marvels at a machine that can fill 165 cans in just 5.5 seconds.

Meanwhile, Cherry Healey is learning how four basic ingredients – water, malted barley, hops and yeast – can be manipulated to make dark, heavy ales, light, fragrant lagers and everything in between. She is also uncovering the secrets of the perfect pint in a scientific study which shows that drinking beer from a curved glass makes it taste fruitier, while a frothy head and a higher temperature also improve flavour. Which is a win for the traditional British warm pint.

Historian Ruth Goodman is asking why Burton became the centre of brewing in Britain in the 19th century. The answer is that it is all in the water. The hard water there was perfect for brewing flavourful stouts and porters. While its position on the canal network made it ideally placed to transport finished beer round Britain and beyond. She is also finding out how beer got its stereotypically blokey reputation, despite the fact that brewing was traditionally a female profession. It is all down to the introduction of hops in the 15th century, which turned beer making from a cottage industry into an industrialised process.

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.

Gregg Wallace is in Lowestoft, at an enormous factory where they produce 450 tonnes of frozen food each day. He follows the production of frozen potato waffles, from the arrival of 25 tonnes of potatoes right through to dispatch. Along the way he discovers how they make a monster amount of mash and marvels at the technology which stamps out a million identical waffles every 24 hours, each weighing 68 grams and exactly 15 mm thick.

Meanwhile Cherry Healey is learning about the differences between waxy and floury potatoes and finding out which spud you should use for which job. Small waxy potatoes are best in salads and boiled, while floury potatoes produce the best mash and roasties. She's also asking whether, in these carb-conscious days, we're unfairly demonising the potato. At King's College London she meets a dietician who runs tests which show that the potato, gram for gram, has more vitamin C than beetroot and carrot and more potassium than banana. Keeping hold of these nutrients isn't easy. But Cherry is delighted to discover that skin-on wedges, as long as you go easy on the oil, are a nutritional winner.

Historian Ruth Goodman is myth busting Walter Raleigh's connection to potatoes. She discovers that he couldn't have brought them back from North America, because there weren't potatoes there until 20 years after he died. Instead the credit must go to Spanish explorers and an enterprising French chemist called Parmentier, who popularised this exotic new vegetable. She also meets one of the inventors of the potato waffle, who shows her how Mr Whippy ice creams were the inspiration behind this teatime treat.

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 explores the Nottinghamshire factory that produces 250,000 jars of curry sauce each day. Gregg is making a supersized 3,000-kilo batch of tikka masala - enough to feed 25,000 people. He loads in almost half a tonne of yoghurt and cream and ten other ingredients, including 30 kilos - or 10,000 cloves - of garlic. He deploys an unusual kitchen implement - a hosepipe - to get his ingredients into the cooking pot and heats it for 30 minutes. Then he checks it for colour against a decorating colour chart. Finally his jars head into a pasteuriser for a second two-hour cooking session.

Meanwhile, Cherry Healey is in Guntur, the chilli capital of India, where they sell 3,500 tonnes of chilli each day. She helps to harvest the chillies on a typical small-scale farm, dries and packs them down then follows them through processing into chilli powder. Cherry also gets the lowdown on cooking rice with four foolproof rules which ensure it comes out right every time, and learns how to beat the burn if you have overdone it in the curry house. It turns out that milk is the right choice because the fat dissolves the capsaicin that is responsible for that burning sensation.

Historian Ruth Goodman finds that our passion for curry is around 370 years older than the supposed invention of tikka masala in a Glaswegian restaurant in the 1970s. She recreates a 1747 recipe for rabbit curry, and learns that the word 'curry' itself is a misunderstanding of the Tamil word 'kari'. And she re-examines the early convenience curries of the 1970s and talks to the British Asian housewife whose curry crusade helped to make high street curries closer to Indian home cooking.

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.

Gregg Wallace explores the Manchester factory that produces 700,000 toilet rolls a day. He begins 940 miles away in Sweden, where the raw material - wood - is harvested from a sustainable forest of one billion spruce trees. Most of the wood is used for timber, but the offcuts are turned into sheets of wood pulp. Gregg follows this pulp to Manchester, where he learns that two types of wood fibre - long and short - are required for a loo roll, to give it strength but also softness. He watches as 3,750 kilos of fibre are combined with 34,000 litres of water and sprayed into a 40-metre-long, 11-metre-high paper-making machine. It takes just four seconds for the watery pulp mix to be transformed into soft, dry paper. It is then rolled onto a 1.2 tonne supersized toilet roll known as a 'mother reel'. Each one of these gives birth to 25,000 individual toilet rolls.

Meanwhile, Cherry Healey is at Britain's oldest toilet factory, where they churn out 1,000 loos a day. And she gets the bum deal of following the flush through the sewers and water treatment works of Brighton, finding out how sewage is cleared of debris, grease and bacteria, and transformed into clean water in a little over an hour after flushing. She has a cheeky encounter with a high-tech Japanese toilet and heads to Cranfield University to see a prototype toilet that does away with the need for water altogether. Could this be the toilet of the future that gives one-third of the world's population access to efficient sanitation?

Historian Ruth Goodman finds out what was used to wipe with before the invention of toilet paper. She discovers that the weapon of choice in the American midwest was a dried-out corn cob. And that it wasn't until the 1930s that toilet paper was guaranteed 'splinter free'. She is also in myth-busting mode, finally laying to rest the idea that Thomas Crapper invented the modern toilet. She heads into the House of Lords to check out an 18th-century flushing toilet, still in use today, and discovers that the Great Stink of 1858 expedited a period of sanitary invention that led to the toilet we know today.

Gregg Wallace is in Derbyshire at an enormous coffee factory where they produce 175,000 jars of instant coffee every day. He follows the production of freeze-dried instant coffee, from the arrival of 27 tonnes of Brazilian green coffee beans right through to dispatch. Along the way he chills out in a freezer cooled to -46 degrees Celsius and discovers how they give you that hit of freshly brewed coffee smell when you pierce the foil lid. They extract the aroma and put it back in just before the instant coffee granules head into the jars.

Meanwhile, Cherry Healey learns about the chemistry of coffee. She finds that roasting alters its chemical composition, and listens for the 'first crack' as steam splits the bean along its seam. She also goes cold turkey on caffeine, giving up her coffee habit for five days to understand how this most commonly used psychoactive drug affects her body and brain. She discovers that the caffeine withdrawal headache is due to increased blood flow to the brain. And she is at Kew Gardens, where they have concerning evidence revealing that climate change is affecting coffee harvests worldwide. Cherry samples a brew made from the beans of a coffee species that could cope in these warmer growing conditions, and which could ensure a future for the daily cuppa.

Historian Ruth Goodman investigates the origins of instant coffee. She tastes a version that looks very like axle grease which was drunk during the American Civil War in the 1860s, and finds out why it began being referred to as 'a cup of Joe'. She also visits the site of the UK's very first coffee house, which sprang up in a London churchyard in 1652, and learns that the early passion for coffee led to the founding of modern institutions, including the Stock Exchange, auction houses and newspapers.