Tuesday 27 June 2017

Sweet science of chocolate

Crystals and how to perfect that desirable “melt in the mouth” effect

Sarah Hayes

The taste of chocolate is partly determined by the ingredients and the recipe used to make it, but there are other factors to consider.

The taste of chocolate around the world tends to reflect the history of chocolate making in that part of the world and the requirements of different countries and climates. For example, here in Ireland we do not have to worry that our chocolate will melt due to the high outdoor temperatures, whereas this would be a much more significant concern in Australia.

Chocolate’s essential ingredient is cocoa butter, a type of fat. This fat has six different potential crystalline forms, which means that there is a significant crystalline part to chocolate. The difference between the six is how the chocolate is tempered, or cooled.

The ability of a substance to take on different crystal forms is known as polymorphism. It generally means the ability of something to exist in multiple forms. The word ‘poly’ means many, and ‘morph’ means shapes. The different forms are due to atoms and molecules that make up the crystal, and the type of crystal that form  determines the taste.

Research into polymorphism is very important in the Synthesis and Solid State Pharmaceutical Centre (SSPC) and has many different applications. When we apply this to chocolate we know that one of the six polymorphs of the cocoa butter has a much better and nicer taste and texture when compared with the others. So, naturally, this is the one that chocolatiers aim to achieve in their product. The best polymorph is form V. This chocolate has a glossy shiny texture, breaks well and evenly and has a superior taste.

So how do chocolatiers ensure that they get the desired polymorphic crystal form? The process is known as tempering. If chocolate is melted above 36°C, the form V crystals melt also, and as the chocolate hardens and cools other types of crystals can form, leaving it dull and splotchy. All of the crystals have a range which they melt in and the form V melts from 34°-36°C. This is just under body temperature of 37°C, which is why we have that lovely ‘melt in the mouth’ sensation when eating chocolate.

Typically the chocolate is melted to over 40°C to ensure that all potential six forms of crystals are melted, and as it cools all types of crystals form randomly. Then the chocolate should be cooled to about 29/30° C to allow crystal types V form. This provides us with tiny ‘seed’ crystals, which serve as nuclei to create small crystals in the chocolate.

The chocolate is then heated to 31/32°C to ensure that all other crystal types are eliminated. After this point any further re-heating of the chocolate will destroy the ‘temper’ and you have to start again.

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