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Low-fat chocolate: a dream come true (Image: Spencer Wilson)

They said it couldn’t be done – but tasty half-fat chocolate is here. And we have a recipe that you can try at home

WITH his mop of brown curls and horn-rimmed specs, Stefan Bon could easily carry off Willy Wonka’s top hat and purple jacket. I’m less convinced by the small beaker of greyish gloop being stirred in an industrial blender in his lab at Warwick University, UK. Bon’s cheerful admission that he more usually comes up with new recipes for paints, industrial coatings and the like isn’t exactly whetting my appetite, either.

But appearances can be deceiving. The uninviting contents of that blender might be all my dreams come true at once, not to mention those of chocoholics the world over: the secret ingredient for smooth and creamy chocolate with half the fat, just as much flavour – and which is an appetite suppressant, too. As I fantasise about that possibility, Bon’s PhD student Adam Morgan draws a syringeful of goo, squirts it into a beaker of melted chocolate and dramatically freezes it solid with a splash of liquid nitrogen. So is this the real deal? There’s only one way to find out.

“The unappetising contents of that blender might be all my dreams come true”

Bon and Morgan are not the first scientists to grapple with the challenge of how to make low-fat chocolate that melts in the mouth and tastes right. A typical chocolate bar, milk or plain, contains about 30 per cent fat. That fat earns its keep. The cocoa butter and milk fats are what give chocolate its taste and texture. Take them out, and you get chocolate that is harder and doesn’t taste as good.

And those are not the only important differences. The shiny, melt-in-the-mouth texture of a chocolate bar, and that satisfying snap when you break off a chunk, come from the way cocoa fats crystallise as molten chocolate cools. The fats can settle into one of six possible crystal structures – known as polymorphs – each with a slightly different melting temperature.

The “sweet spot” is reached with the formation of polymorph V. In this configuration, , which brings the melting point closest to body temperature. If you have ever wondered why chocolate never tastes the same after it has melted in the sun and solidified once more, it’s because .

“The sweet spot comes when the fat is tightly packed, melting at close to body temperature”

If you want to take some of the fat out of chocolate, you have to replace it with something that doesn’t affect the polymorph V structure. Nothing else will do, as several companies have discovered to their cost.

In the 2000s, most attempts focused on replacing the fat with air bubbles – nanometre-scale holes, not the big ones that give some chocolate bars their distinctive textures. Nestlé, Unilever and Mars have all filed patents. But air bubbles can be trouble. Add enough of them to replace a significant proportion of the fat, and the chocolate begins to feel unsatisfyingly light.

Water bubbles fared no better. While it helps retain the chocolate’s heft, water carries the unappetising risk of droplets joining up to form puddles or sinking to the bottom of the bar. In any case, adding even a small amount dampens that crisp breaking sound and can cause a “bloom” – the powdery-white coating that can form on the surface of chocolate when it hasn’t been stored properly.

Then, last year, food scientist Peter Fryer and his team at the University of Birmingham, UK, made a with water droplets. They adapted a technology normally used to make low-fat margarine, adding gelatin to keep the melt-in-the-mouth feel while stopping the water droplets from pooling. The results were good enough to convince someone: the team sold the patent, which is now being developed in secret by the food industry.

Of course, not everyone likes meat in their sweets: gelatin is made from animal skin and bones. So Bon started investigating a different approach, using a trick from the paint industry. With Tom Skelhon, also at Warwick, he crafted using a combination of a food additive called fumed silica and chitosan, a carbohydrate derived from the shells of shrimps. You need some kind of acid to make the recipe work, so Bon used fruit juice. If you don’t want the chocolate to taste fruity, though, you can use dissolved vitamin C or flat cola.

It worked. In a paper published last year, they reported that their chocolate – with 50 per cent of the fat replaced by the fruit-juice mixture – had the right polymorph V structure. But Bon wasn’t convinced that the public, and hence chocolate manufacturers, would bite. “You have to declare nano-ingredients on the label,” he says, which tends to scare off manufacturers . And because it comes from seafood, chitosan could pose an allergy problem. “Anyway, I’m a perfectionist,” he says.

That was when he realised there was another material that would avoid both these problems. This time, inspiration came from the cosmetics industry. “We put tiny little jellies in oil for other things,” he says, such as thickeners for body scrubs. “Why not chocolate?”

The jelly they chose to pad out the chocolate was agar, a substance made from algae that is widely used as a thickener in food and also by researchers as a solid base on which to grow bacteria. If you heat it the right way, it will solidify at the same temperature as chocolate. Mixing agar solution into the chocolate led to the formation of perfect, 30-micrometre distributed evenly throughout. At this size, your mouth cannot tell the difference. Voilà – a smooth, creamy batch of polymorph V, containing half the fat by volume.

What’s more, because agar is about 80 per cent fibre, it’s a lot more filling than traditional chocolate. So even though, technically, you could eat more of the chocolate for the same amount of fat, you might not want to.

And there’s yet another bonus. Unlike silica’s acidic requirements, the agar can be mixed with any liquid – including alcoholic drinks. “The vodka version didn’t taste particularly nice,” says Bon, but he is looking forward to trying out Baileys or amaretto.

Food scientists are already salivating. “Fat replacer is something the food industry is very keen to have,” says Jianshe Chen of the University of Leeds in the UK. He’s particularly impressed with the way Bon’s team finessed the water into a convincing chocolate texture.

But back to the : how does it taste? Fresh from the blender, it tastes pretty darned good. Just like melted chocolate. My low-tech home-made version (see “Make it yourself“), which I spiked with dark rum, has finally tempered in the fridge. It looks a little darker than normal chocolate, but texture-wise you’d never know the jelly was there. Or the rum, for that matter. I can’t vouch for any appetite-suppressing properties, though. I ate the lot.

This article appeared in print under the headline “Choco-lite”