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 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.