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Developing the perfect shape
Christoph Hartmann
It’s a scientific fact: a chocolate bar needs to have just the right shape for the flavour to be optimally released.
©Giorgio Pesce Atelier Poisson

What happens when a mechanical engineer likes chocolate? He obviously wonders what shape his ideal bar of chocolate has to have to melt as perfectly as possible on his tongue. Around 300 experts like Christoph Hartmann are working at one of Nestlé’s four Research Centres. Automobile designer Christoph Hartmann knows that it is worth looking into the mouth of a chocolate-lover to create a bar of chocolate with the ideal shape.

Testing chocolate in order to study it

As an engineer at the Nestlé Research Centre, I spend most of my time thinking about chocolate: what shape does the ideal bar of chocolate have to have to develop an optimal taste? The average chocolate-lover might find this question superfluous. But chocolate-lovers who examine this question more thoroughly will come to the conclusion that there are, in fact, major differences.

The individual pieces of the chocolate bar, its rectangular form and its thickness are optimised to make it easy to pour the chocolate mass and to remove the solidified chocolate. And although the grooves make individual pieces of the chocolate bar easy to break off, an efficiently formed piece of chocolate does not really fit very well in our mouths. Not only that: the form of the food we eat has a powerful influence on our sensory organs.

How does chocolate melt in your mouth?

In order to find the perfect form, I first examined the human mouth. I procured a plaster cast of it and compiled some geometrical data that gave me precise details – down to the last millimetre – of the shape of the mouth. Aided by an expert in computer simulations, I calculated the heat-transfer processes between the oral cavity and the chocolate.

I was now able to establish the criteria for designing a perfect form. Later on, I consulted the expertise of a chocolate-maker on my team, as well as some scientists involved in sensor technology and aromatics. We not only wanted to give the chocolate bar a nicer shape, but also to find a form in which the chocolate’s taste could unfold as perfectly as possible – without changing the recipe or the ingredients.

Sweet, sweeter, sweetest

I soon had an initial series of prototypes ready. The prototypical forms all had the same weight, but an individual and, on the whole, contoured form. We gave our prototypes to specially trained chocolate testers. They commented – based on a detailed test protocol – on the intensity of the sensory properties: i.e. the texture, aroma and taste of the chocolate. We then statistically evaluated the data to establish the difference between the prototypes.

The result confirmed our hypothesis: independently of the ingredients and the recipe, the form of the chocolate influences our sensual perception. And there really is a difference whether we let a chunk or a slightly contoured piece of chocolate melt in our mouths. Depending on the form, the chocolate dissolves slower or faster, tastes sweeter or more bitter.

We also wanted to gain a better understanding of the physico-chemical processes that occur when chocolate melts in our mouths. Using a special technology, we were able to measure how the aromas are set free while a piece of chocolate melts in our mouths. To this end, we had the testees put on masks with small tubes so that we could analyse the vapour set free in their nostrils when the chocolate melted. Our instrumental analyses showed that some prototypes released more aroma than others.

The secret of the surface

When we had found the perfect form, we created an industrially producible chocolate shape. This provided the basis for the bar on sale in shops. It is still rectangular, but the surface of the individual pieces of chocolate now resembles a gently contoured wave.

Ultimately, there is chocolate and there is chocolate: the recipe, flavourings and sensory properties of bittersweet and milk chocolate differ greatly from one another. Consequently, in addition to the bittersweet version, we have also developed a shape for milk chocolate whose properties differ from the bittersweet variety.

Will our considerations also convince consumers? Our consumer tests, at least, suggest that they do. My personal tip: the chocolate that tastes best is the one with the wavy form: especially if you have the curved side facing upwards on your tongue and the narrow piece of chocolate pointing towards the tip of your tongue.

Christoph Hartmann works at the Nestlé Research Center in Lausanne, where he manages a team of twelve scientists. The entire project from the beginning to market maturity took 24 months.


Lenfant F, Hartmann C, Watzke B, Breton O, Loret C, Martin N., "Impact of the shape on sensory properties of individual dark chocolate pieces." International Journal of Food Science and Technology, vol. 51, issue 2, May 2013, pp. 545–552

Pionnier E, Ali S, Hau J, Antille N, Robert F, Hartmann C., "Using PTR-MS to study the impact of chocolate piece shape on in vivo aroma release," Poster, 4th International PTR-MS Conference, 2009

Christoph Hartmann


Christoph Hartmann started his professional career as a mechanical engineer in the automotive industry in 1997. He joined the Nestlé Research Center in Lausanne in 2006, where he investigated the mechanisms of in-mouth food breakdown. Today he is a group manager at Nestlé R&D China and heads the Nestlé Food Safety Institute in Beijing.

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