The science behind great chocolate

The process for making the best chocolate has been revealed by researchers studying a 140-year-old mixing technique, and could lead to both greener and lower-fat products.

Chocolate truffles

Scientists have uncovered the physics behind the process responsible for creating chocolate’s distinctive smooth texture. A team led by the University of Edinburgh studied mixtures resembling liquid chocolate created using the process - known as conching - which was developed by Swiss confectioner Rodolphe Lindt in 1879. The findings may hold the key to producing confectionery with lower fat content and could even help make chocolate manufacturing become more energy efficient.

The analysis, which involved measuring the density of mixtures and how they flow at various stages of the process, suggests conching may alter the physical properties of the microscopic sugar crystals and other granular ingredients of chocolate. Until now, the science behind the process was poorly understood.

Molten chocolate

Wilson Poon
Professor Wilson Poon

The new research also reveals that conching – which involves mixing ingredients for several hours – produces smooth molten chocolate by breaking down lumps of ingredients into finer grains and reducing friction between particles.

Professor Wilson Poon, of the University’s School of Physics and Astronomy, who led the study, says: “We hope our work can help reduce the amount of energy used in the conching process and lead to greener manufacturing of the world’s most popular confectionery product. By studying chocolate making, we have been able to gain new insights into the fundamental physics of how complex mixtures flow. This is a great example of how physics can build bridges between disciplines and sectors,” he says.

Before the invention of conching, chocolate had a gritty texture. This is because the ingredients form rough, irregular clumps that do not flow smoothly when mixed with cocoa butter using other methods.


The project took around seven years from conception to publishing the findings. Professor Poon says: “Conventional understanding of conching is that the process acts to spread molten cocoa butter over the solid particles which include sugar and milk powders. What we discovered was that, in fact, conching performs two roles; the first of these is to break up irregularly-shaped aggregates of solid particles - this improves how particles can pack together and improves the flowability of the chocolate paste. The second role of conching is to spread a soy-derived molecule called lecithin over the solid particles. This molecule acts to reduce the friction between particles, which improves flow further. These two roles act together to give molten chocolate its distinctive smooth mouthfeel.”

According to Professor Poon, this understanding may allow chocolate manufacturers to optimize their processes to reduce the amount of energy required for conching, and so help towards move towards greener manufacturing.

“Soft-matter physics gives insight into the structure, processing and stability of many industrial products, including a variety of foods”, he says. “Physics can shape what we eat by helping to understand the roles of certain ingredients in recipes and formulations and allow manufacturers to ‘tune’ their recipes to achieve a variety of perceived benefits without damaging the distinctive properties of many brand products. Thus, our work on chocolate may help manufacturers reduce the amount of fat in their products.”

Slurries and pastes

chocolate conching
Conching is a long process of intense mixing, agitating, and aerating of heated liquid chocolate. The long intense mixing action assures complete coating of every solid particle with cocoa butter, giving the chocolate a well developed and delicious flavor and texture.

The team’s insights could also help improve processes used in other sectors – such as ceramics manufacturing and cement production – that rely on the mixing of powders and liquids.

“We are currently using the knowledge gained from our work in chocolate to develop understanding in other industrial sectors where mixing the powder with small amounts of liquid to achieve high-solid-content but flowable slurries and pastes,” says Professor Poon.

The study, published in Proceedings of the National Academy of Sciences (PNAS), involved a collaboration with researchers from New York University. The work in Edinburgh was funded by Mars Chocolate UK and the Engineering and Physical Sciences Research Council.

Related links

School of Physics and Astronomy

Journal paper in PNAS