Mad About Science: Chocolate

By Brenden Bobby
Reader Contributor

I think everyone’s overdue for a little comfort food, and what better food to comfort one’s soul than chocolate?

Chocolate has a long and storied history, dating back to at least 1000 B.C.E. Chocolate comes from processing the beans of the cacao tree native to the Amazon basin. The trees themselves were cultivated as crops by many Mesoamerican civilizations, including the Aztec, Maya and Toltec peoples. Cacao was such an important part of Mayan culture that important people were often buried with bowls of cacao beans to take into the afterlife. The beans were also used as a currency, as well as being consumed in a liquid form for religious ceremonies.

You may be envisioning a garbed priest chugging an ice cold glass of chocolate milk, but it was likely this stuff was more like cocoa-beer or some kind of fermented syrup. Modern chocolate beverages are mixed with milk and cane sugar to sweeten them, neither of which were likely readily available to the Aztecs for religious ceremonies. Imagine drinking a 98% cacao chocolate bar with no sugar and a warm bottle of unsweetened kombucha — suddenly it makes sense why this was reserved for special occasions.

Cacao beans being processed into
chocolate on the island of Grenada. Photo by Ben Olson.

Aside from the amount of sugar added to a chocolate bar you’d find at the local grocery store, the process to create this tasty treat hasn’t changed much in 3,000 years. Cacao pods are harvested from trees and cut open to extract the beans from the fruit. The beans are then fermented and dried before they are sent off to be roasted. During the roasting process is when the beans become chocolate brown, it’s also the point in which the cacao begins transitioning into cocoa — worth noting, this distinction is fairly minor, and it’s similar to the difference between lava and magma, cocoa is simply refined cacao while lava is just magma that reaches Earth’s surface. 

After the roasting process, the beans are run through a machine to be cracked and winnowed. This breaks away the inedible shell around the bean to extract the part intended for consumption. This process can be a little complicated now that much of it is automated. The roasted beans are fed into a machine by a hopper and then agitated by metal teeth to separate the nib from the shell. 

As you can imagine, separating the nibs from the shells by hand would be a nightmarish prospect when you’re accounting for the sheer amount of chocolate being produced to meet market demands, so a machine was developed to do it for us. This machine vibrates the nibs and the shells on a series of screens that filter out larger chunks of shells, allowing nibs and fine shell particles to fall into a chamber where a vacuum whisks away the tiny shell particles.

Once separated from the inedible material, the nibs are fed into a grinding machine where they’re rolled for several days until they transform into a fine powder. Cocoa powder is used in a number of applications from health supplements to pouring into a mug of hot milk. Often during the grinding process, other materials such as milk, sugar or water are added to change the consistency of the cocoa to influence the final output of the product, making it smoother or sweeter. This is called conching.

The next step is to temper the chocolate. This involves heating the chocolate to just the right temperature so that it has melted, but hasn’t burned. This gives the manufacturer the ability to pour the chocolate into a mold to form it into a desired shape, such as a bar or a bunny. You can effectively temper chocolate at home using a double boiler, which is effectively a set of two pans. The pan closest to the heat is filled with water, while the top pan is filled with chocolate. The water helps control and even the spread of heat while you stir the chocolate, keeping the chocolate from burning anywhere it touches the pan.

If you’ve learned nothing else scientific from this article, here’s a fun term to impress your friends: tempering chocolate is an example of “reversible change.” If you were to temper chocolate and pour it into a mold, you could temper it again and pour it into a different mold to change it repeatedly. However, if you put that same chocolate into some baking flour and make a chocolate cake, no amount of tempering will return that chocolate to a bar state. That is an example of “irreversible change.”

Can you think of some examples of reversible and irreversible change in your everyday life? Chocolate is unique in that it’s an organic compound that can undergo both forms of change. Something like a peanut or a tomato or their byproducts cannot. Water is fairly unique in that it can undergo reversible change, but it’s extremely difficult to force it into a state of irreversible change. Throwing a bar of chocolate into an industrial forge will char it and break it down into baser compounds of hydrogen, carbon and oxygen. Throwing an ice cube into that same forge will cause the ice to melt and evaporate, but as soon as those compounds enter an area that’s considerably cooler, they will reform back into water.

This reversible change is the entire basis of the water cycle, and life as we know it on planet Earth — including the life of the cacao tree that provided the beans for the chocolate bar you’re currently craving.

Stay curious, 7B.