Gregg Wallace is in Cornwall at an enormous bakery where they produce 180,000 Cornish pasties a day. He follows the production of the pastry snacks from the arrival of two tonnes of swedes right through to dispatch. Gregg learns that there are very specific rules to creating a Cornish pasty. They must be made in Cornwall, the filling can only contain onion, potato, swede, beef and some seasoning - and each ingredient must be cooked from raw within the pastry parcel.

Meanwhile, Cherry Healey is delving into the wonderful world of the onion. She peels back the layers to discover the science that makes it such a versatile vegetable, and more importantly, why it makes us cry. It is all down to a chemical called lachrymatory factor, which is only created when an onion is cut into. Cherry visits an anaerobic digestion plant, where they turn waste from food factories into electricity. Micro-organisms feed on food waste, producing methane gas, which is used to power generators.

Historian Ruth Goodman is debunking some common Cornish pasty myths. It has been claimed that the county's tin miners invented the pasty as a convenient snack to eat while they toiled at the rock face. She learns that miners may have eaten them, but they didn't invent them. And it is unlikely that they used the pastry crimp as a handle. She also visits the Worshipful Company of Grocers in London, which was responsible for importing pepper into Britain. She learns how this ubiquitous seasoning transformed from a commodity so valuable it was known as black gold to a spice that everyone could afford.

In Wigan, Gregg Wallace visits an enormous soup factory, which produces two million tins a day. He follows the production of vegetable soup, from a pea harvest in Yorkshire right through to the finished soup going into cans and being dispatched. Along the way, Gregg watches as a five-tonne avalanche of peas – around a million individual peas – is frozen within two hours of being picked. He mixes up three tonnes of veg and 500 gallons of tomato sauce and watches as they are combined and packed into 10,000 tins. Gregg is astonished by a 27.4m-tall pressure-cooking tower and surprised to learn that for every one degree drop in temperature in winter, the factory observes a 3.5% increase in soup sales.

Meanwhile, Cherry Healey is measuring the vitamin content of fresh and frozen vegetables. She finds that her sample of frozen peas have six times the vitamin C content of fresh, while sprouts do even better with 800% more. Cherry travels to a rock salt mine outside Crewe, which supplies half of all salt used in the UK food industry, and runs an experiment to see if soup could be the answer to staying fuller for longer.

Historian Ruth Goodman is cooking up a batch of ‘soop of buttered spinach' from the 17th-century cookbook of Robert May. This is the first reference to a recipe for soup in English, but the resulting sweet, vegetable puree doesn't resemble soup as we know it today. She also heads to Poplar in east London to a Salvation Army soup kitchen. Here, Ruth discovers that the notion of the soup kitchen originally began in 1795 as a response to a countrywide harvest failure.