The wonder that is chocolate has been enjoyed since 1500BC. From early Mayans, to the Aztecs, London finally opened a chocolate shop in 1657. We enjoy chocolate all year round. From selection boxes to Easter eggs, you can’t get away from it, and who would want to? Strangely, the higher a country’s chocolate consumption, the more Nobel prize winners it has! So while you tuck into that chocolate biscuit with your cup of tea, what is the science behind our beloved chocolate?
Have you ever had a melted chocolate bar on a hot day and put it in the fridge to harden again? Did you notice a white coating when you took it out of the fridge? This coating appears due to how the chocolates structure has changed as it was heated and cooled again. Cocoa butter (i.e. the fat from cocoa beans) gives chocolate its structure. Chocolate is tempered (i.e. heated and cooled to improve properties such as consistency or hardness), and it is the structure of the cocoa butter which is manipulated during this process. The first step of tempering is to heat/melt the chocolate, destroying the cocoa butter crystals. The chocolate is then cooled to a precise temperature (~50°C) where a different crystal structure of cocoa butter forms. Cocoa butter has a few different crystal forms (i.e. different shapes depending on the temperature it is cooled to), and by cooling to 27-28°C produces the desirable No. 5 crystal. Crystal form No. 4 is also produced in small amounts during this cooling. This type of crystal is not desired so the chocolate is reheated to remove these, leaving only desirable form No. 5. Tempering can be achieved by stirring melted chocolate in a bowl and cooling on a cold marble surface. However, companies like Cadburys, Hersheys (etc.) have automated this process on an industrial scale.
Sounds simple? Unfortunately cocoa butter crystals are more awkward than this. Crystal form No. 5 is sought after but not the most stable structure, meaning that over time the crystals stabilise to form No. 4 which are bigger and take away the glossy finish on most chocolate; This is called a fat bloom. This happens more with soft centred chocolates as the fatty oils in the fillings can promote crystal growth of type No. 4. If you want chocolate with a glossy finish, almost glass like, you need to make the crystals as small as possible with a very controlled tempering process. Crystal size also affects flavour. The smaller the crystals, the better the flavour release as the crystal structure melts in the heat of your mouth. Chocolate naturally has 3x as many aromatic components as red wine, so enhancing that flavour with small crystals is vital!
Despite its wonderful taste, chocolate can be deadly. How does this wonderful substance cause such harm to other species? A compound found in chocolate is theobromine (an alkaloid, a class of naturally occurring organic nitrogen-containing bases). This compound is poisonous to other species such as cats and dogs whose tolerance is much lower. Lethal dose 50 values (i.e. the amount of substance it would take to kill 50% of the population) in a human are 1000 mg/kg, whereas in cats it’s only 200 mg/kg, and in dogs 300 mg/kg. These values vary depending on species and breed, but you can see that it takes a lot less to poison a dog with chocolate than it does a human, although it is possible (bad news for me!). Theobromine is more concentrated in dark chocolate than other types (i.e. milk, white). Strangely, rats and mice have a tolerance nearer to a human’s than that of dogs or cats. This toxicity is due to how species metabolise (i.e. break down) the theobromine. At toxic levels this leads to acute nausea, convulsions, internal bleeding and often lethal over-stimulation of the heart. Humans can metabolise theobromine a lot more effectively than dogs and cats.
Thankfully we can enjoy chocolate on behalf of our furry friends, and to make it even more enjoyable chocolate chemists (yes, that is a job and yes, I wish I was one) are developing lower calorie chocolates with the same taste! One such success has been created by chocolatier Aneesh Popat. This London based maths graduate, and chocolatier, coined the idea of water-based truffes. Conventional truffles have cream or milk based fillings which take away from the natural chocolate flavour, whilst adding to the fat content. Aneesh’s truffles used a water-based filling meaning that you can really taste the chocolate as water is tasteless, and they still appear creamy when eaten! The water ganache has 40-50% fewer calories than that in normal truffles (the chocolate encasing it is just as bad for us as usual though…I’m not complaining).
You’d be surprised at the amount of research which goes towards the production of our sweet dreamy chocolate. At the University of Birmingham research is underway into making a lower fat chocolate, again by using water. The water substitution is undetectable and uses 10-15% less cocoa butter than standard chocolate. If methods such as this are successful, it could have a huge impact on the confectionary industry. Companies such as Cadburys see low fat chocolate as the ‘Holy Grail’. Imagine how many dieters would see a lower calorie/fat content chocolate bar and be swayed? There is a lot more interesting science involved in food production than you may have originally thought, so consider it when you next enjoy your favourite chocolate.
Chocolate image from: http://www.the-chocolatier.co.uk/