Introduction
The cocoa bean is the seed of the tropical cacao tree and is used to make cocoa powder, chocolate from cocoa liquor, and cocoa butter. There are three main varieties of the cocoa plant: Forastero, Criollo, and Trinitario, with Forastero comprising between 80% and 90% of the world’s cocoa production. Worldwide production of cocoa has grown by nearly 200% in the last forty years to reach over 4.5 million metric tons in 2013. Nearly two-thirds of the world’s cocoa beans are produced in African nations and Ivory Coast and Ghana alone produce just under 50% of worldwide cocoa production. Most of the rest of the world’s cocoa is produced in Asia, South America, and tropical areas of North America. The process begins by harvesting pods from the trunk and branches of the cocoa tree. Pods have a tough, leathery rind, typically contain thirty to fifty seeds, and are filled with a sweet pulp. The normal amount of time for pods to become suitable for harvest is three to four weeks, meaning the same trees can be harvested multiple times in one season. In some countries, harvesting of cocoa pods can occur year-round. Within a week to ten days after harvesting, the pod is cut open, the rind is discarded, and the pulp and cocoa seeds are removed. Pulp and seeds are laid out and covered, usually with mats or banana leaves. The thick pectin-containing pulp liquifies as it ferments in a process known as sweating and trickles away during fermentation over a week to ten days. This process is important for bean flavor since it helps reduce the bitter flavor found in the beans when they are harvested from the tree. If the pods are harvested prematurely, then beans can have a low cocoa butter content or sugars in the pulp can be insufficient for fermentation, both of which can result in a weak flavor. After fermentation is complete, the beans are usually shuffled and left to dry in the sun. Beans must have a low moisture content before shipping in order to reduce the risk of mold and mildew contamination. In recent years, beans are often shipped in large bulk containers to reduce shipping costs. These containers can hold up to several thousand tons of beans in one container or a number of smaller twenty-five-ton containers.
Chocolate Manufacturing
Upon arrival at a chocolate manufacturing facility, the dried beans are cleaned to remove any unwanted material. Beans are then roasted to bring out the flavor and color. Roasting time, temperature, and degree of moisture depending on the type of beans used and the desired end product. A winnowing machine removes the shell from the beans, leaving just the cocoa nibs. The nibs (dried internal portion of the cocoa bean) are heat-treated to kill any possible bacteria before the alkalization process begins. Alkalization (also known as Dutching) is designed to manipulate the pH to further develop the flavor and color. Nibs are soaked in an alkali solution (usually potassium carbonate). Further roasting is needed after the Dutching process to dry the beans and enhance flavor. Depending on the desired end product, alkalization can occur either on the cocoa cake or chocolate liquor later in the manufacturing process instead of on the cocoa nibs, but the most common method is to perform it on the nibs.
Cocoa nibs are milled to make liquor paste. There are different types of grinders used in this process but all of them grind the nibs to release fat, sometimes in multiple stages. The process yields particles of cocoa suspended in cocoa butter. Temperature and degree of milling are adjusted according to the desired product specifications. For many chocolate products, different kinds of beans are used and blending them to the required formula often occurs at this stage. The cocoa liquor is pressed to extract and separate cocoa butter from the solid particles. The leftover solid mass is known as cocoa press cake. The amount of fat present in the press cake is inversely proportional to the amount of fat extracted from the liquor and this can be controlled by the manufacturer. At this point, the processing takes two separate directions to make cocoa powder from the solids and chocolate from the cocoa butter. The cocoa press cake is broken up and pulverized to form cocoa powder. Cocoa powder is known for its health benefits while containing very little sugar and fat compared to chocolate.
The leftover cocoa liquor forms the base for making chocolate. The three main types of chocolate are dark chocolate, milk chocolate, and white chocolate. Dark chocolate contains sugar, cocoa butter, cocoa liquor, and may or may not contain vanilla. Milk chocolate contains the same ingredients but adds milk or milk powder, has a smaller proportion of cocoa butter, and will always contain vanilla. White chocolate contains the same ingredients as milk chocolate without the cocoa liquor. After the mixing of ingredients, the mixture is refined by pressing through a series of rollers, which forms a smooth paste. This process improves texture. The mixture then undergoes conching, which is running the mixture through a mixer and agitator that evenly distributes the cocoa butter within the chocolate. Temperature is controlled and can vary from 120°F for milk chocolate to 180°F for dark chocolate. Air flowing through removes some unwanted acids and reduces moisture. The material is powdery and mixing coats the particles with fat, redistributing the substances from dry cocoa into the fat phase. Conching changes the particles from dry to pasty to liquid and additional fats and emulsifiers can be added to change viscosity near the end of the process.
The final stage of making chocolate is known as tempering. When the fats in cocoa butter crystallize, it can result in crystals of six different sizes because of polymorphous crystallization. This results in an untempered appearance and can cause the chocolate to crumble rather than snap when broken. The six crystal sizes have different melting points and physical properties. The idea of tempering is to assure that only the best form is present, which has a melting point of 93°F, a glossy but firm texture, and snaps clean when broken. Chocolate is heated to 113°F to melt all crystals and then agitated while cooled to 81°F. At this point, two forms of the crystals will be present. The chocolate is then heated to about 88°F to only leave the desired form of crystal remaining. Excessive heating of the chocolate at this stage will require restarting the tempering process. After tempering, the chocolate is poured into molds, cooled, and is ready for packaging. Chocolate is sensitive to temperature and humidity. Ideal storage conditions are around 60°F with a relative humidity below 50% and in a dark place for unwrapped chocolate.
Conclusion
NIR spectroscopy has emerged as a tool for rapid, non-invasive, and cost-effective analysis of parameters of interest in cocoa & chocolate that could potentially replace traditional reference methods. Classification and quality assessment of cocoa beans are of paramount importance in chocolate manufacturing. Different varieties of beans present diverse chemical composition and make it difficult to standardize parameters during processing. Important parameters in cocoa beans include protein, fat, moisture, ash, carbohydrates, fermentation index, pH, total polyphenols, and color measurements. Methods for testing these parameters are time-consuming and often require skilled technicians and wet chemistry methods. One example of this is the Conway method, used to measure gas quantitatively by a specific reagent or enzyme. This technique is used to measure ammonia nitrogen (NH3) in cocoa beans, a good indicator of fermentation time. NIR spectroscopy can be used in-line during the manufacturing process as well. One example is measuring cocoa butter crystal content parameters during tempering of chocolate, which is the essential final processing step during manufacturing. Viscosity, enthalpy, and slope values (a function of a cooling curve and exit temperature in a crystallizer) have all been correlated to NIR spectra using calibration models, showing the potential for real-time, on-line monitoring of the chocolate tempering process. All of these parameters and measurements have been studied using NIR spectroscopy with results showing the potential to replace traditional reference methods.
References
International Cocoa Organization – How Exactly Is Cocoa Harvested?
https://www.icco.org/faq/58-cocoa-harvesting/130-how-exactly-is-cocoa-harvested.html
International Cocoa Organization – Processing Cocoa
https://www.icco.org/about-cocoa/processing-cocoa.html
Cocoa Guide: How to Process Cocoa Beans
https://www.asanduff.com/cocoa-guide-process-cocoa-beans
Alkalizing Cocoa and Chocolate
http://www.blommer.com/_documents/Blommer_Alkalizing_Cocoa_and_Chocolate.pdf
Lesson – Tempering Chocolate and Why
https://www.ecolechocolat.com/en/chocolate-tempering.html
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https://www.sciencedirect.com/science/article/pii/S0168169916301284
Non-Destructive Determination of Cocoa Bean Quality Using FT-NIR Spectroscopy – Sunoj, Igathinathane, Visvanathan, Computers and Electronics in Agriculture 124 (2016) 234-242
https://www.sciencedirect.com/science/article/pii/S0168169916301284
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