GUEST BLOG – the physics of chocolate making

Written By – Arhama Gufran

Chocolate -a word we are all familiar with. Whether you are a kid ,a teenager, or an adult, no
matter who you are, what do you like about them the most?
Is it their taste that delights you
Their ability of blending with your moods makes you their crazy fans? Do you know the
mechanism behind chocolate making?
It’s physics that works everywhere!

“Physics not only works for the subatomic inside the atoms but works equally hard for fixing our relationship with our dearer ones”

Working with chocolates is often called an art, but the complex physics of chocolates, a
substance that in some ways behaves more like steel than any other foods-means
chocolatier’s kitchens are also working science labs!


cocoa butter,sugar,full cream milk powder,cocoa liquor,lecithin,vanilla and cocoa.
Chocolate manufacturing requires two main processes to be done:

(1)CONCHING: A process in which solid sugar, milk and cocoa powder are mixed with liquid

By subjecting the granular mixture to heat ,mechanical action and adding oil dispersants at
precisely timed stages, chocolatiers can transform the ingredients into homogenous, flowing
liquid-solid suspension.

The process has been mastered for well over a century but until now there has been little
knowledge of the physical mechanism involved in the process.

The new insights in the process have been gleaned by an international team of
physicists, led by Wilson Poon at the United Kingdom’s Uni of Edinburgh. In their study Poon
and his team used a simplified formulation of chocolates and analysed the process.

The researchers identified and measured two key parameters underlying the process:

(a)Yield stress of mixture: it is the stress at which the mixture starts to deform irreversibly.
(b) By subjecting its viscosity to high shear, they found that these values are controlled by
how far the mixture is from it’s jamming volume fraction (the point at which the fraction of solids in the mixture becomes too high for mixture to flow freely.)

The mechanical action breaks down groups of solid particles. This raises the mixture’s
jamming volume fraction. After oil dispersant is added, the friction between the particles is
reduced further increasing the jamming volume fraction. Eventually, the jamming fraction becomes so high that the inhomogeneous granular mixture transforms into a homogenous fluid, where all solid particles are suspended evenly within the liquid.

(2)Tempering: Since cocoa comes in six different forms, liquid-solid suspension when melted
completely and have been recrystallized, can give you six different forms of chocolates. But
not every form is our favourite.

For a chocolatier, to find the temperature at which form five is obtained, is a must, as this is the
point where the prize lies. This is the form that melts in your mouth and not in your hand, the
type that has glassy appearance, the type that has that sharp snap when you break a piece!
This is your (mine as well:) chocolate!!

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