Chocolate. As addicting as it may be, ever wonder how chocolate comes to taste as amazing as it does? The rich and creamy taste of good sweetness in your mouth every time you take a bite out of your favorite chocolate bar just seems too irresistible. Or maybe you’re one of those people who prefer the aerated chocolate bars, infused with gas and is even creamier than regular chocolate. No matter your preference, the beautiful and unique taste of chocolate is due to the rigorous and complex processes it undergoes. Consistency is perfection and is tied directly to thermodynamics and the chemical compounds that are integral in the production of chocolate. From cacao bean to the bar you wish you were holding in your bar right now, let it be put that the perfect chocolate is not as easy to make as it may seem.
Figure 1. Theobroma cacoa, the cacao tree.
First, the cacao pods from the cacao tree Theobroma cacoa are harvested and the beans and pulp are extracted from the pod. They are left to ferment for a few days and then laid out in the sun to dry. Roasting the beans is one of the most important steps in making chocolate. It kills the lingering mold and bacteria (because that wouldn’t be too yummy to ingest now would it?) The roasting of the beans is also what changes the flavor and removes some of the bitterness. Now to the chemistry. The cacao bean is comprised of 55% fat, 12% protein, 11% fiber and 6% starch. Roasting the beans removes fatty acids that are unwanted such as ethanoic acid. The roasting generates a chemical reaction called non-enzymatic browning, more specifically, the Maillard reaction. The Maillard reaction occurs when the carbonyl group of sugars reacts with the amino acid group and produces N-substituted glycosylamine and water. It then undergoes the Amadori rearrangement to form ketosamines that react further with brown nitrogenous polymers. The reactions of the Amadori rearrangement inclue mainly fission, dehydration, and degradation At this point, the beans have off-flavors and off aromas. But have no fear, these bitter and rancid-smelling beans do become the sweet chocolate we all enjoy and love through a few more processes. The beans are ground into cocoa liquor and then pressed to separate the liquor from solids. The solid is also known as cocoa butter and this key ingredient continues onto conching and tempering to become chocolate.
Conching removes volatile compounds such as methanol and acetic acid, as well as adjust moisture content and viscosity. This is a mixing process that aerates the mixture for 24-60 hours at 110°F, to stimulate interactions between ingredients and molecules. As this occurs, flavor and aroma develop as acidity and the bitterness of the cocoa are lost and moisture content is reduced.
Tempering is but a complex cooling process, to make the cocoa butter seeds uniform in size and shape and to stack these molecules tightly together in a nice crystalline structure. Imagine a bunch of LEGOs, all different shapes and sizes. If piled together, it is not very efficient and unstable. But, if packed tightly and orderly, the structure is stable. The process of tempering is simply stacking cocoa butter seeds to be as stable as possible.
The main component of tempering is temperature. As the chocolate cools, the cocoa butter forms stable and unstable seed crystals. These crystals are proportional to the six different crystalline forms of cocoa butter. This means that the atoms are the same but they may be arranged differently. Relating back to LEGOs, there are many different types of arrangements but it will always be the same types of LEGOs you use to create something. The ability of having multiple arrangements or shapes is called polymorphism. It is found that the tastiest, most stable, and ideal form is Form V, or beta crystals. The melting point for the Form V polymorph is about 33.8°C, about 92.8°F. This temperature is about the temperature of a person’s mouth, unless they submerged their tongue in something cold for a long period of time. Because this polymorph’s melting point is nearly identical to our mouths’ internal temperature, chocolate basically spontaneously melts, which is chocolate is so irresistible. The lower the melting point of the polymorphs, the thicker and stickier it feels in the mouth. Polymorph VI, unfortunately, is produced after 4 months a room temperature, has a higher boiling point and is much more stable. Fats melt quickly because the carbon atoms within the fat form long chains of atoms. Intermolecular forces affect these chains, so the more fat chocolate has, the faster it melts due to the intermolecular forces caused by the carbon chains.
Figure 2. Different cocoa butter polymorphs and corresponding melting points.
Figure 3. Form V Polymorph
To keep only stable beta seed crystals, the chocolate is warmed again to a temperature between the melting point of beta crystals and the temperature at which beta crystals form. The mixture is then cooled at around 13-15°C, or 55-59°F, to promote preferential growth of the stable crystals. If the temperature were too high, the cocoa solids and other dry ingredients from the cocoa butter would separate, thus resulting in a dry paste. Likewise, if the chocolate’s moisture level increased even the slightest, the dry particles in the mixture would be saturated and detach from each other, maintaining a liquid form. Though this does not result in a chocolate bar, it is a useful technique to add water to chocolate when making chocolate sauces or syrups.
Figure 4. Comparing the compactness and stability cocoa butter polymorphs.
Speaking of different forms of chocolate, believe it or not shape and type actually do contribute to taste. These are components that affect how the chocolate breaks up in the mouth, thus it is opinionated on whether you prefer a normal chocolate bar to an aerated one, for example. The cocoa crystals in chocolate are about 0.01 to 0.1mm in diameter. This microscale structure however varies slightly with the way the chocolate is molded. Normal chocolate bars are molded after tempering while aerated chocolates receive a blast of a certain propellant. These propellants can vary from nitrogen to argon to regular CO2 or even nitrous oxide, also known as laughing gas. This gas is infused into the chocolate and turns the chocolate into a foam with the use of a siphon. After siphoning, the chocolate is cooled in a low pressure environment, like a vacuum, to let the gas bubbles expand. Depending on the propellant used, the sizes of the bubbles also alter the taste of the chocolate. A study funded by Nestlé proved that chocolate foamed with nitogen and nitrous oxide had more intense tastes due to the larger bubbles these gases produced.
Figure 5. A chef using a siphon to aerate chocolate into a foam.
“Aerated chocolate is more gentle and creamy. Its density is so low that it takes seconds for the chocolate to meld down in the mouth. That is why its taste is so exquisite and great,” says Stephen Becket, a former researcher for Nestlé. This is because aerated chocolate is lower in density and has a lower melting point, being only more sensational in the mouth and stimulating what is called mouthfeel. No wonder truffles seem to just melt into your soul whenever you pop one into your mouth. It’s always been about chemistry.
We can all admit that chocolate is an amazing sweet itself, whether it’s satisfying a crave or bestowing this great treasure upon a significant other on Valentine’s Day. What’s even more amazing is how chemical and mechanical processes are able to turn a bitter cacao bean into the beautiful joy that eating chocolate may bring us all. With these processes, the most important thing to keep in mind is consistency. Our senses are able to discriminate taste based on the texture of chocolate and its feel, and that’s pretty cool. Just think the next time you taste your favorite chocolate, think not only of how it became that perfect shape and texture but how because of the way it feels on your tongue, your taste buds cannot seem to thank you enough.