In a kitchen in the south of England, two women are devising a recipe that could change the world. James Flint reports

On a kitchen table two young women have assembled a variety of items. There are brown bottles, bags of white powder, a pestle and mortar, a collection of funnels, a roll of silver gaffer tape. There is a drill. There is a whisk.

Are they making bombs? Are they making drugs? No. They are doing something far more likely to change the world we live in. They're making their own version of Coca-Cola.

Codenamed "Merchandise 7X", the list of ingredients that go into Coke - 922 million litres of which were drunk in the UK last year - has been kept carefully shrouded in mystery since the drink's inventor, a medicinal chemist called John Pemberton, first wrote it down in 1886. These days it is supposedly kept under 24-hour guard in a vault in Atlanta, Georgia, which is odd considering that author Mark Pendergrast published it in his exposé of the cola industry For God, Country & Coca-Cola (Basic Books) in 1993. The company maintains that this recipe is not the same as the one it uses.

Kate Rich and Kayle Brandon are bar managers at the Cube Microplex, an "alternative" cinema in central Bristol. Opposed in principle to the business and environmental practices of the Coca-Cola corporation, the Cube bar has never served Coke. That doesn't mean there isn't a demand for it. "We'd tried Pepsi and Virgin Cola and various others too," says Brandon, "but they weren't really a positive alternative. They were acceptable, but they weren't Coke. And people really want Coke."

After conducting various taste tests, they felt the preference had less to do with flavour than the power of the brand. Any alternative they were going to offer had not only to taste almost identical but overcome the incredible pull of Coca-Cola's marketing. "Given that most of the Cube's customers come because they like the place's DIY attitude," Brandon explains, "one way of doing that was to make the cola ourselves."

Cola is basically a mix of caramel, caffeine, sugar, fizzy water, citric or phosphoric acid, and eight essential oils. It's the precise blend of these oils that lies at the heart of the 7X secret formula. A trawl of the web soon uncovered several 7X-type recipes, the most promising of which was adapted from the one in Pendergrast's book.

But turning the recipe into a palatable drink turned out to be more difficult than it looked. "The oils we had to import from the US," says Rich. "The caramel had to be sourced direct from DD Williamson, a large operation based in Manchester which actually provides the caramel for all the Coca-Cola manufactured in the UK. And the caffeine we found at MyProtein.co.uk, a body-building website."

When they had assembled most of the kit, they invited friends along to an "open lab" to help them make the drink. "Unfortunately none of us had any scientific knowledge whatsoever, and it's quite a scientific process," says Rich. "We spent half our time running out to get ingredients that we didn't have, and we kept having to go round to the local post office to weigh things on their parcel scales."

Though they came up with something like cola by the end of that first day, they couldn't replicate their success. The problem was getting the oils to mix with the other ingredients, a process called emulsification, or binding together.

The emulsifier used in most soft drinks is dried acacia sap, better known as gum arabic. But Rich and Brandon couldn't get this to work. "We managed to destroy a whole series of kitchen mixers, completely trashed them. The gum arabic scoured the sides, the blades snapped ... it was really violent and very distressing."

After the fourth mixer went west they realised it was time to seek help. A mass email to the Cube's mailing list uncovered Dr Peter Barham, adviser to the Fat Duck restaurant and expert in food emulsification. He pointed out that they were using the wrong kind of gum arabic. "We'd bought ours from the local Indian food shop, but it wasn't particularly homogenous, so each time it was giving us different results."

Barham also pointed out that making an emulsion was all about force. Rich and Brandon had scaled up their quantities, but not their mixing power. They were looking forlornly at the constituents of their cola lab when they noticed the tubular metal handle on one of their hand whisks was about the same thickness as a large drill bit. Bingo! Whisking the mixture with a hammer drill produced the desired effect.

All they needed to do now was to add caffeine, caramel, sugar, citric acid and sparkling water - and suddenly, from a single cup of emulsion, they had enough cola for a month.

So how does it taste? First, we try the real Coca-Cola. A restrained sweetness, low cool notes of caramel, dry on the tongue, quite flat on the palette. Very refreshing, but with little depth.

Now for Rich and Brandon's home-made product. The initial surprise is that it really does taste like Coke. Very slightly sweeter than "the real thing" but less acidic. A satisfying, complex flavour, subtly different from the brand leader, but easily as good.

Having found their liquid gold, Brandon and Rich plan to sell concentrate kits to other small bars and businesses. They maintain that they are not out to challenge the Coca-Cola hegemony, but they "do hope that along the way we'll help produce a small reality-shift. It's social change through science and baking. Sort of DIY aesthetic meets the WI."

The mega corporation remains unfazed. "As the saying goes, imitation is the sincerest form of flattery," says a Coca-Cola spokesman. "But our product is unique. Anyone with a selection of ingredients could make a type of cola, but there can only be one Coke."

Thanks to Rich and Brandon, we have a much better idea of what that really means.

Brew it yourself

NB. 1 batch of 7x formula will produce three batches cola syrup, or approximately 54 litres of cola.

Step 1: 7x formula:

Using food-grade essential oils, assemble 3.75ml orange oil; 3ml lime oil; 1ml lemon oil; 1 ml cassia oil (nb. reduce cassia content for next production); 0.75ml nutmeg oil; 0.25ml coriander oil (6 drops); 0.25ml lavender oil (6 drops); 0.25ml neroli oil (optional/removed due to high cost).

Using a measuring syringe, measure out the oils into a glass or ceramic container. Keep covered to avoid volatile oil fumes escaping. Then dissolve 10g instant gum arabic (equivalent to 22ml) in 20ml water (low calcium/low magnesium, Volvic is good) with one drop vodka - Cube uses Zubrowka. (Be aware that total quantity of vodka will be 0.0007ml per litre of Cube-cola).

Place the gum/water/vodka mix in a high-sided beaker - stainless steel or glass are best. Using a high-power hammer drill with kitchen whisk attachment, whisk the gum mixture at high speed while your assistant droppers the oils. Mix in steadily with the measuring syringe. Continue to whisk at high speed for 5-7 minutes, or until the oils and water emulsify.

The resulting mixture will be cloudy. Test for emulsification by adding a few drops of the mixture to one glass of water. No oils should be visible on the surface. You now have a successful flavour emulsion, which should hold for several months.

Step 2:The mixers

This makes two allied concentrates, Composition A and Composition B, which can be stored separately before being mixed into cold syrup with the addition of sugar and water.

Composition A

Mix 30 ml double strength caramel colouring (DD Williamson Caramel 050) with 10 ml water. While stirring, add 10ml 7x flavour emulsion (oils/gum/water mix).

Composition B

Mix 3 tsp (10ml) citric acid with 5-10ml water, then sieve in 0.75 tsp (2.75ml) caffeine. Mix thoroughly using a pestle and mortar until caffeine granules are no longer evident. The mixture may behave erratically, turning either white or clear for no apparent reason. If it goes white, add more water. Pass through muslin or jelly bag to remove any anomalies.

At this point, A+B can be packaged separately and later reconstituted into cola syrup.

Step 3: The cola syrup

2 litres water; 2kg sugar

Compositions A & B

Make a sugar syrup (mix in a cooking pot on low heat to dissolve quickly) using 1.5 litres of the water and all the sugar. Filter if unsure. Mix Composition A into the remaining 500ml water. Add Composition B, then the sugar syrup. You now have 3 litres Cube-Cola syrup or approx 18 litres cola.

Step 4: The cola

As required, make up your cola as a 5:1 mix, five parts fizzy water to one part cola syrup. Cube uses 350ml syrup in a 2l bottle of Tesco Ashford Mountain Spring. This cola recipe is released under the GNU general public licence.

· For more information see www.gnu.org

www.sparror.cubecinema.com/cube/cola