Dr Michelle Dickinson, also known as Nanogirl, is an Auckland University nanotechnologist who is passionate about getting Kiwis hooked on science. Photo / Glenn Jeffrey
Dr Michelle Dickinson, also known as Nanogirl, is an Auckland University nanotechnologist who is passionate about getting Kiwis hooked on science. Photo / Glenn Jeffrey
This week, Mike Hosking brought a fun fact to the nation showing us you can't melt a Flake in a microwave. Being a dedicated experimentalist, I committed my week to eating and heating chocolate, purely for research purposes, of course.
The experiment is simple and easy to do at home. All you need is a chocolate flake bar and a solid milk chocolate bar. I used Cadbury's Flake and Dairy Milk bars for this experiment, as their ingredients list showed both contained full cream milk, sugar, cocoa butter, cocoa mass, milk solids, flavours and emulsifiers.
The bars were placed on a plate in the microwave and cooked on high for one minute.
The experiment was repeated by heating chocolate on a plate held over a pan of simmering water for five minutes to remove microwave effects.
Using oven mitts, I removed the plates from their heat and discovered a liquid mess where the Dairy Milk once was and a Flake bar that seemed unchanged other than the burning smell it emitted.
To understand what happened, we first need to understand why things melt. When a solid absorbs heat energy, its molecules start to move around more quickly.
If enough similar molecules are touching each other, they stop staying fixed in a solid crystal lattice and loosely join together to form a melted liquid.
Chocolate is made by heating and mixing tiny particles of the raw ingredients together to bind them. The mixture is then cooled and reheated to specific temperatures for exact periods of time in a process called tempering. Tempering is important in making chocolate, as it controls the crystal size that the particles reform into, which then determines the melting temperature, taste and texture of the final chocolate product.
First heat your chocolate... Photo / Glenn Jeffrey
Most chocolate is tempered to produce beta-2 particles which give a dark brown, glossy chocolate that snaps when broken, but chocolate can also be tempered to form beta-1 particles that produce chocolate which is lighter in colour, matte and will crumble instead of snapping.
By breaking both chocolate bars between my fingers, I found that the Flake crumbled, was lighter in colour and more matte compared to the darker, snapping dairy milk implying that the flake probably has more beta-1 sized particles.
This means that although the ingredients are the same, the size and structure of the crystal particles in the bars is probably different, which is why they look and behave differently.
Melting occurs if enough of the same type of molecules come into contact when heated, so they can join together to form a liquid. If they aren't close enough to contact each other, the molecules heat up individually instead of joining other molecules, and eventually burn down into a powder.
As the cocoa butter is the most likely ingredient to melt in the chocolate, the results suggest that the Dairy Milk has a structure where the cocoa butter particles are in continuous contact with each other, so when heat is applied they slide around the sugar and cocoa particles to form a liquid.
But the Flake probably has a structure in which the cocoa butter particles don't touch, which could be due to sugar and cocoa particles separating them, as well as the open gaps created by the layered structure.
So a difference in particle size and distribution of cocoa butter in the chocolate is most likely causing the Flake to survive the microwave test.
I also discovered that science is always better when you can eat the results. This column is sponsored by Callaghan Innovation to promote the coverage of science and innovation. The views expressed are the author's own.
