Inside the Factory

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 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 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.

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 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 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 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.