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Kodaikanal: There are the Swiss and the Belgians to thank, of course, but humans owe their deepest debt for rich, tempting chocolate to someone, or something, else: Physics.

A team led by researchers at the University of Edinburgh studied the process used to make chocolate, and uncovered just how complex physics transforms brittle non-homogeneous ingredients into the creamy, textured delicacy the world loves.

The process, conching, itself dates back to a happy “accident” in 1879, but the exact science behind it has so far not been very well understood.

With the study allowing a look at the molecular-level interactions between ingredients, the scientists said it might spell good news for chocolate lovers by paving the way for the development of low-fat varieties.

The study is also expected to yield energy efficiency in cement and pharma industry, where products are often derived from similarly heterogeneous mixtures of solids and liquids.

University of Edinburgh researchers behind the study were assisted by physicists from Utrecht University, the Netherlands, New York University, US, and University of Cambridge, UK, with colleagues from InProcess-LSP, the Netherlands, ExxonMobil Research and Engineering Company, US, and Mars Chocolate UK Ltd serving as corporate partners.

Published in the Proceedings of the National Academy of Sciences (PNAS) last week, the research was funded by Mars Chocolate UK Ltd and the Engineering and Physical Sciences Research Council, UK, a research funding agency.

A savoury ‘accident’

Until the 19th century, chocolate wasn’t the delicacy it is today — it was hard, brittle, and not everyone’s dessert of choice.

But a young chocolatier changed it all in the 1870s. Born in 1855, Rodolphe Lindt, the son of a Bern-based pharmacist, took it upon himself to make a delicacy out of chocolate.

According to the website of Lindt, recognised as pretty much the gold standard by chocolate lovers, he bought an old factory with antiquated machinery and got to work trying to stir it into a palatable texture.

His experiments and recipes didn’t yield results until one Friday in 1879 when he left the factory without switching off the machine churning the chocolate — whether by accident or design is not known. When he came back Monday morning, “what he found in the stirring tank was anything but hard, burnt chocolate mass. It shone; it smelt wonderful”.

This process has since come to be known as “conching”, which involves the transformation of an inhomogeneous mixture of fat, sugar and cocoa solids into a homogeneous flowing liquid.

The word “conching” comes from the Spanish word “concha”, which means shell. Conche is a shell-shaped vessel used for holding and mixing various ingredients to make chocolate.

Conching paved the way for chocolate to be made into bars and other confectionery items, where it was mainly consumed as a drink before.

But the process demands time and energy: The conching process for low-quality chocolate may take around six hours, while a mild, rich one may burn up to 78 hours.

Since the conching process is of utmost importance for the chocolate’s final flavour and texture, manufacturers keep its details proprietary.


Also read: The world just can’t get enough chocolate


‘Smooth mouthfeel’

The researchers behind the new study sought to understand the exact process involved in conching, and traced it to two primary factors: The mechanical breakdown of lumps of ingredients into finer grains, and the reduction of friction between particles with the use of an essential body fat, called lecithin.

In the first role, irregular shaped aggregates of solid particles are broken into smaller, finer pieces. This improves the flowability and packing of solid particles within the chocolate paste, the researchers found.

In the second role, conching spreads lecithin over finely-grained solid particles. Lecithin reduces friction between constituent particles and thereby smoothens their flow.

“These two roles act together to give molten chocolate its distinctive smooth mouthfeel,” professor Wilson Poon of the University of Edinburgh, who led the study, was quoted as saying by the FoodIngredientsFirst website.

Industrial applications

Through this study, researchers have laid bare the microscopic physics of how the addition of surfactants — molecules that help befriend substances in different phases, like solid and liquid — may help create the maximum flowable solid content. Lecithin acts as a surfactant in the chocolate-making process.

These insights have wider applications in sectors that rely on mixing of powders and liquids, like ceramics manufacturing, pharmaceuticals, cement production etc.

“It is interesting that by studying a subject as practical as chocolate-making, we have been able to derive new insights into the fundamental physics of how complex mixtures flow, and then use these insights to help industries very far removed from chocolate manufacturing,” Poon said in a press statement accompanying the study.

“It is a great example of how physics can build bridges between disciplines and sectors.”


Also read: No more chocolate by 2050? Why we need to understand what’s at stake


Mywish Anand is a winter intern at Kodaikanal Solar Observatory. He has a Master’s degree in Computational Physics from the Central University of Punjab, Bathinda.

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