This NBC Learn video uses the process of chocolate-making to explain chemical reactions related to heat and temperature, including melting point and the formation of crystalline structures. (Untempered Chocolate photo: Courtesy of Katreece Montgomery)
The Chemistry of Chocolate
HODA KOTB, reporting:
It is the reason chocolate is so widely seen as a token and expression of love, given as a gift to a sweetheart or a treat to oneself. It is the reason chocolate is the most frequently craved food, worldwide: Chemistry.
Yes, because of the chemicals in chocolate that affect the brain: caffeine, a stimulant. Theobromine, a mood-lifter. Tryptophan, which helps the brain make serotonin, a happiness chemical.
But also because of the chemistry behind this: the smooth shine and rich texture of chocolate, especially dark chocolate. The way it melts in your mouth, and tastes on your tongue. In fact, dark chocolate is a great way to look at several basic chemistry concepts, starting with temperature, heat reactions, and melting point.
JULIE YU (The Exploratorium): So today we are going to be melting some chocolate.
KOTB: Julie Yu is a scientist at The Exploratorium in San Francisco, who’s funded by the National Science Foundation.
YU: Chocolate is composed of cocoa solids, cocoa butter and some sugar, and at room temperature, it’s in a solid form. The melting point of a substance is the temperature at which it experiences a change, so it will turn from a solid to a liquid.
KOTB: A change from one common state of matter to another. Why does chocolate’s melting point matter to chocolate-lovers?
YU: One of the key reasons chocolate tastes so good to us is, in fact, its melting point. Our body temperature is 98.6 degrees and the melting point of chocolate is somewhere around ten degrees lower than that. And if you’ve ever held a chocolate bar in your hand for too long, you probably experienced that it melted in your hand.
KOTB: And, that chocolate melts even faster in your mouth, which unless you’ve been drinking something cold, or out in the cold with your mouth open, is usually between 75 and 80 degrees Fahrenheit, pretty close to the melting point of chocolate.
YU: As it reaches its melting point in the high 80 degrees Fahrenheit, you can see that it’s turning into this nice viscous liquid.
KOTB: In chemistry, how viscous a liquid is, its viscosity, is a measure of a fluid’s thickness, and how slowly it flows. As dark chocolate softens in your mouth, it starts to flow over your tongue, a pleasurable sensation known in the food industry as mouth-feel.
As it melts, it moves over hundreds of taste buds and that is key to our perception of chocolate’s taste: more than 1,500 flavor components have been identified in chocolate, making it one of the most complex chemical mixtures known.
YU: The components of chocolate are cocoa solids, cocoa butter and sugar. There’s actually no water in there. It’s cocoa butter as a liquid, not water.
KOTB: Heat isn’t just a factor in making chocolate solid or liquid, it is a major factor in making chocolate itself from cocoa beans, seeds of the cacao tree that are fermented, dried and roasted, all processes that involve heat or heated air. Roasted beans are ground-up, filtered, mashed and pressed into a cocoa butter mix, usually in giant machines, which also produce heat.
YU: Through mechanical friction, rubbing the chocolate together, it gets finer and finer so that the consistency is something that’s smooth in our mouths, and not grainy.
KOTB: What happens next is the reverse of chocolate melting in our mouths:
the smooth, liquefied cocoa butter mix will harden into chocolate as it cools, going from a liquid state to a solid state.
YU: When chocolate hardens, what’s really happening is the cocoa butter that’s present is solidifying, and the fat molecules that are inside the cocoa butter form a crystalline structure.
KOTB: But chocolate that cools and hardens too fast forms seed crystal structures that, like most structures built in a hurry, are substandard, disordered.
YU: You can think about a pile of Legos that you collect, into a pile, and if you do it really quickly, they will be every which way, and that’s kind of representative of a loose crystalline structure.
KOTB: Result: chocolate that’s dull, blotchy, soft. What works better?
YU: To actually join the Legos one by one into a tighter packed crystal structure.
KOTB: Which chocolate-makers do in a process called tempering, carefully controlling the temperature and rate at which the liquid chocolate cools, so that what are called beta or Form 5 seed crystals form, in a tight crystalline structure.
YU: And it gives us that nice consistency and shine that we like.
KOTB: Or love.
The world’s chocolate industry is driving deforestation on a devastating scale in West Africa, the Guardian can reveal.
Cocoa traders who sell to Mars, Nestlé, Mondelez and other big brands buy beans grown illegally inside protected areas in the Ivory Coast, where rain forest cover has been reduced by more than 80 percent since 1960.
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