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 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.