We ventured into the world of processed produce to see how they make "the stuff we eat". It wasn't an easy task. Many manufacturers refused us entry. We had thought milk would be a good place to start. The management of Parmalat, the Italian-owned company that produces Paul's milk, would not let us see how the milk is processed, citing safety reasons. Kellogg's said that discussing this sort of matter "was not the sort of thing we do".

Nestle said it was not interested in discussing how Nescafe was made, instead offering us inside knowledge about a new range of ice-creams. We politely declined. A few, however, welcomed Epicure with open arms, happy for us to take a peek behind their security cordon. Among them was Kraft, the American company that has made Vegemite in Port Melbourne for the past 86 years. Vegemite

THE Vegemite plant smells of yeast, like a winery during vintage, only sweeter. It's basically a series of big rooms stacked with stainless steel tanks connected to other stainless steel tanks by stainless steel pipes. The world's annual production of 23 million jars of vegemite is made here; 95 per cent of those are consumed in Australia and New Zealand. The rest are sold mainly to expat Aussies and Kiwis. A few make it to Tokyo, where umami-mad locals wolf down tiny frozen cubes of Vegemite in modern sushi bars. When I mention to our hosts from the marketing department the popular conception that Vegemite is made from "beer sludge", they shrug their shoulders. We are soon down at the receiving tanks into which tanker trucks pump their loads of spent yeast, collected from the nations' breweries. All the action takes place within the stainless steel pipes and vats. The first stage filters off any remaining malt and hops and removes residual alcohol. The remaining yeast is then treated with heat and enzymes to remove the outside of the cell wall and to leave the rest of the yeast cell: protein, amino acids and B vitamins. This is cooked with salt at low pressure for four hours and is now referred to as yeast extract. It has been reduced by 40 per cent to a viscous liquid that looks like hot caramel sauce.

Our host takes a sample of the liquid. Like Augustus Gloop from Willy Wonka and the Chocolate Factory I can't help but taste this proto-spread. Compared with the finished product it is bitter, yeasty and aromatic with the flavours of the hops and barley still upfront; it's a long way from being Vegemite. To finish the process, the contents of more than 30 of these drums are sucked up into a large stainless steel vat and further reduced. Liquefied cooked onion and liquid celery seed, a small amount of caramel for further colour and flavour, and both sea salt and mineral salt are added. This goes into another cooker at more than 100 degrees for several hours, where further caramelisation takes place. What has become "black velvet" spread is extruded warm into jars and sealed.

FOUNDED: Vegemite was invented by chemists working at Fred Walker's eponymous cheese company, and was first sold commercially in 1923. The same company invented a beef extract called Bonox in 1918. In 1926, a company was formed with Chicago-based Kraft to make processed cheese in Australia. After Fred Walker's death in 1935, the Australian holdings of the company were absorbed by Kraft in Chicago. DID YOU KNOW? Australians spread 1.2 billion serves of vegemite on toast and bread every year.

Skippy Cornflakes THE assumption that most breakfast cereals are made from a baked or fried slurry is not supported by a tour of the Skippy Cornflakes plant at Cooranbong near Newcastle, a factory surrounded by farmlets and small creeks. About 80 tonnes of cornflakes are made every week from kernels of corn that have been steamed and dehulled, so only the starchy inside remains. During the process the whole corn kernels are broken in half to form "grits" about 4 millimetres big. These grits are cooked in a giant pressure cooker with water, raw sugar, salt, malt extract, vitamins and minerals at a temperature above 100 degrees for two hours. During this process the water hydrates the starch, making it swell and gel. Sugars react with the protein in the corn, creating a deep ochre-gold colour, a process known to learned cooks and chefs as the Maillard reaction. The pressure cooker is opened to reveal slightly swollen and translucent grits that, when squeezed, feel as if they are made from a blend of plastic and elastic. They are poured onto a belt, cooled, separated and dried under a blast of hot air.

Rollers drag and pull the cooked grits, causing some of the starch particles to break apart. When the flake is baked at about 200 degrees, this denatured starch forms the body of the flake, while the intact starch particles blister, causing the rough surface. The flakes are cooled and sent off for packing.

FOUNDED: Skippy Cornflakes are made by the Sanitarium Health Food Company, established in Australia in 1898 by the Seventh Day Adventist Church to promote vegetarian food. Sanitarium is one of a few Australianowned processed-food companies. DID YOU KNOW? Sanitarium's first baker trained under Dr John Harvey Kellogg and worked from a rented bakery in Melbourne. Four'n Twenty Pies

THE Four'n Twenty pie brand and recipe were bought by Gippsland baker Patties from US-owned food giant Simplot in 2003. Patties' massive purposebuilt plant stands on the Princes Highway on the Lakes Entrance side of Bairnsdale. Every second week the plant — and surrounding industrial estate — is enveloped in the aroma of baking pastry and cooking meat as it turns out 21,000 175 gram pies an hour, six days straight, 24 hours a day. Mindful of the old "lips and arseholes" myth, it's a relief to find that Patties uses 27 kilogram boxes of 85 per cent lean frozen beef and mutton, mostly shoulder meat. The meat comes ready boned, but the boxes are still X-rayed for bone and stray metal before being minced coarsely.

In a gleaming one tonne cooker, 490 kilograms of meat is cooked with water and fresh grated carrot and onion. When the mixture comes to the boil, more meat is added. This is repeated until all the meat is cooked. The meat needs to hit the cooker when the liquid is at boiling point so each morsel contracts and holds its shape. A slurry of pre-mixed maize starch, salts, pepper and spices is stirred through while the mix is cooking. Safety measures involve further X-raying and magnet checks for small, hard materials. Meanwhile, in the pastry room in another part of the plant, the upper crust of puff pastry is mixed in a 250 kilogram blender. Flour, salt, pastry relaxant and margarine are mixed and then rolled out in a continuous sheet of pastry.

This passes under a long, thin, flat tube from which flows a continuous coating of margarine. The pastry is folded and flip-flopped across itself 62 times, dusted in flour and allowed to relax for 30 minutes before being rolled out to two to three millimetres and sent to the filling line. The pie bottoms are made with a basic dough of flour, shortening and salt that is blended, rolled and sent to the filling line. This is rolled over a tray of sharp-edged pie tins and stamped in with a rubber foot.

The hot filling is piped in, the puff pastry rolled over, spray glazed, pressed and the excess pastry pulled away like a giant piece of lace. The pies roll into a tunnel oven and are baked for 12 minutes. FOUNDED: The first Four'n Twenty pies, about 50 a day, were baked in Bendigo in 1947 by Les McClure. DID YOU KNOW? While other pies declare themselves beef pies, Four'n Twenty is a meat pie, as it contains mutton. The mutton and spices give this pie its characteristic flavour.

Twisties IF YOU'VE always thought Twisties were a deep-fried junk food, you're wrong. Admittedly, vegetable oil is the second-listed ingredient, but Twisties are initially cooked using pressure and friction. Having unsuccessfully spent more than a month trying to find someone at Smith's Snackfood Company to discuss making Twisties, we tracked down a former employee who gave us the inside knowledge. A thick paste of corn and rice meal is run through an extruder or press: imagine a children's Play-Doh toy. There are two plates with holes, one moving, and one stationary.

As the paste is pushed through it develops its random shapes which expand under the heat from the friction. At this stage, they are quite blandlooking compared with their bright-yellow finish. From here, they are baked until dry and crisp. The Twisties are then coated with oil and tumbled with powdered whey, cheese powder, salt, monosodium glutamate, lactic acid and two types of food colouring. FOUNDED: Twisties were first made in 1950 by General Foods and then by Smith's in 1964. Twisties are now made in factories in Adelaide and Perth and the brand is owned by US fast-food giant PepsiCo.

DID YOU KNOW? German-made Twisties are sold in Italy under the brand name Fonzies. THE POTATO CHIP — WHY IS IT SO?

In 1853, a patron at Moon's Lake House in America ordered fried potatoes with his meal. The diner complained that the potatoes were too thick and sent them back to the kitchen. The cook, George Crum, was upset at the criticism. Crum sliced a new batch of potatoes paper-thin, fried them in boiling oil to a crisp, and then salted them. What was intended as a stunt turned into an instant hit — the fussy patron and his friends loved the "crunch potato slices". Soon they became known as Saratoga Chips and were soon served in restaurants up and down the east coast. Potato chips first became available in grocery stores in 1895. Now US retail sales of potato chips are worth more than $US6 billion ($A8.5 billion) a year.