The researchers have found new clues to understanding the microstructure of chocolate and what happens when it turns grey with age.
Dérick Rousseau and of the School of Nutrition, at Ryerson University, in Toronto, Ontario, and Paul Smith of the YKI, Institute for Surface Chemistry, in Stockholm, Sweden have used temperature-controlled environmental electron scanning electron microscopy (SEM) to look at the needle-like spikes of cocoa butter that scatter light and make chocolate turn grey either if it has been stored too long or has been exposed to even small fluctuations in temperature as small as 2 degrees Celsius.
Fat blooms occur because chocolate is extremely sensitive to temperature. Just a 2°C fluctuation will cause the cocoa butter to melt, then recrystallise, forming needle-like structures that scatter light, giving a dull appearance.
The team studied the surface of chocolate as it aged using a scanning electron microscope (SEM), which fires electrons at the surface and measures the electrons knocked back from it to build a picture of the surface with very high resolution.
They found that where the chocolate surface was rough, blooms were far more likely to form.
Rousseau says that if manufacturers were to minimise the amount of surface imperfections, this would be a good way to reduce blooms.
The team demonstrated the same effect in chocolates with soft centres. Filled chocolates were even more susceptible to fat bloom as the liquid-state fat found in the fillings migrates quickly through the chocolate to the surface, accelerating bloom formation and ultimately making the chocolate very soft.
Nigel Sanders, senior research scientist at Cadbury in Toronto, Canada, said that "as an industry, we haven't got to the bottom of what tools we have to stop bloom formation from happening."
"Companies as large as Cadbury do their own research - but never gets published. It's nice to see an academic study that helps the whole industry, and isn't just for the big boys," he added.
The study is published in the Royal Society of Chemistry journal, Soft Matter.