Origins of Solid Chocolate
In 1847, the British company J.S. Fry & Sons revolutionised the chocolate industry with the introduction of a solid chocolate tablet made from cocoa powder, sugar, and cocoa butter. While chocolate beverages had been enjoyed for millennia, this marked the first mass production of chocolate in solid form.
Since Fry & Sons’ innovation, food scientists have continued to refine chocolate-making ingredients and techniques. By the late 19th century, for instance, confectioners began incorporating powdered milk into chocolate, resulting in a creamier texture that delighted consumers.
Today, the chocolate industry is a thriving global enterprise, with projections indicating that it could generate approximately $147 billion by 2026. Whether it’s affordable chocolate or gourmet delicacies, ongoing research is paving the way for products with more consistent flavours. Scientists are delving into various aspects, such as the influence of microbes, the process of crystallisation, and the enigma of “blooming” to better understand the chemical and physical changes that contribute to chocolate’s unique taste and texture.
According to Caitlin Clark, a food scientist at Colorado State University, chocolate is “incredibly complex.” Even after a century and a half of chocolate production, there remains much to learn. Below, we explore some of the latest scientific advancements that underpin this beloved cocoa treat.
The Role of Fermentation in Flavour
It has long been established that cocoa-producing regions possess distinctive terroirs akin to those found in wine. The fruity, floral, or nutty notes of chocolate are intricately linked to the environment in which cocoa beans are cultivated. This terroir has traditionally been attributed to a combination of the cacao plant’s genetics and the local soil, climate, and other environmental conditions.
However, in 2017, while working at the International Cocoa Genebank in Trinidad, plant geneticist David Gopaulchan began to suspect that the fermentation process of cocoa beans might play a more significant role in local flavour variations than previously understood. After harvesting the cacao fruit, which resembles a football, the 30 to 50 seeds within—encased in a white pulp—are fermented for about a week in wooden boxes. During this time, yeast liquefies the pulp, consuming its sugars and producing ethanol, followed by other microbes converting the alcohol into acids. This microbial activity results in chemical byproducts known as metabolites, which infuse the beans with unique flavour notes. The pungent vinegar-like aromas of the early fermentation stages eventually dissipate, leaving the beans with a scent reminiscent of “wet socks,” a smell that disappears once they are dried, Gopaulchan explains.
Unlike wine or beer, cocoa farmers do not control the fermentation process beyond occasional stirring, allowing microbes to freely enter and exit the fermentation environment. “It’s a very unpredictable outcome,” says Gopaulchan, now a researcher at the University of Nottingham in England. The fermentation process has largely remained “like a black box.”
Gopaulchan and his team analysed the genomes of the key microbes present at each stage of fermentation across three Colombian chocolate farms. They then trained a computational model to identify the various microbial groups contributing to the diverse flavour notes in chocolate. Certain acetic acid-producing bacteria, for example, were linked to some of the fruitier notes, while the yeasts Torulaspora and Saccharomyces were associated with the classic cacao flavour.
Subsequently, the researchers successfully replicated these flavour notes through controlled fermentation in a laboratory setting. Gopaulchan asserts that this work could lead to the development of a “toolkit” for fermentation, enabling more consistent flavour outcomes. “Fermentation is key to chocolate’s flavour,” he states, recalling that he has previously made unfermented chocolate, describing it as “like eating leaves.” “It has a very green taste.”
The Science of Chocolate Texture
As crucial as flavour is the texture of chocolate, heavily influenced by cocoa butter. Richard Hartel, a food scientist at the University of Wisconsin-Madison, notes, “Chocolate is thicker than most people might imagine.” Hartel and his colleagues are examining the microstructure of chocolate in the forthcoming Annual Review of Materials Research.
Cocoa butter is typically added to the refined chocolate mixture, which consists of cocoa, sugar, and powdered milk, just before the tempering process—a series of carefully designed heating and cooling steps that constitute the final (and often delicate) phase of chocolate production.
Different chocolate products require varying amounts of cocoa butter, which aids in dispersing particles within the mixture and reducing its viscosity—thereby allowing it to flow more easily. When thickness is desired, the chocolate mixture may contain less cocoa butter and more sugar and milk particles, which interact closely, inhibiting flow. This maintains the stable droplet shape of Hershey’s Kisses and chocolate chips as the chocolate transitions from liquid to solid during pouring and cooling. Conversely, for an elegant bar adorned with a cursive logo, higher levels of cocoa butter facilitate the chocolate’s flow, “filling all the cracks and crevices,” explains Hartel.
Cocoa butter also contributes to the ease of breaking, sheen, and delicious melting properties of chocolate, but its solid crystalline structure must be formed correctly. During tempering, the liquid fats in cocoa butter align into a matrix, creating a solid crystalline network. “When the fats crystallise together, they bond with each other, forming a chain,” explains Clark. This process encapsulates flavour particles within the network’s structure.
Tempering is crucial for solidifying cocoa butter into a very specific crystalline form. Of the six possible forms that fat molecules can adopt, “only one gives us that shiny chocolate that snaps when broken and melts just at mouth temperature,” Clark elaborates. If crystallisation fails, chocolate may develop a different melting point, resulting in an unsatisfactory taste. Given the high stakes, tempering is a complex and time-consuming process, prompting scientists to explore potential shortcuts.
For instance, applying ultrasound waves to cocoa butter can induce localised fluctuations in temperature and pressure that may reorganise the molecules. Recent research suggests that this could encourage liquid fat molecules to transition to a crystalline structure without the need for the traditional heating and cooling cycles associated with tempering.
Other researchers have experimented with the incorporation of different lipid molecules, such as phospholipids, which are already present in small quantities in cocoa butter. Adding more of these fats appears to accelerate crystallisation by providing additional sites for crystal growth. When researchers mixed a small quantity of these molecules into both cocoa butter and melted commercial chocolate, then rapidly cooled them to 20 degrees Celsius, they achieved chocolate with the desired snap, sheen, and texture without undergoing the multiple stages of traditional tempering.
Addressing the Issue of Blooming
While the specific crystalline configuration of cocoa butter is essential for creating a delectable product, it carries a potential drawback: the phenomenon known as “blooming,” which manifests as white streaks on the surface of chocolate. This is not mould but rather cocoa butter that has recrystallised into a different form; however, the misconception that it is mould has long plagued the chocolate industry. In addition to its unappealing appearance, blooming can also slow the rate at which chocolate melts in the mouth, potentially imparting a chalky taste.
This cloudy sheen often emerges during storage or transport, especially in warmer or fluctuating temperatures, and scientists do not fully understand the underlying causes. “There is still much debate regarding this,” Hartel states.
Hartel believes the culprit lies within the molecular structure of cocoa butter. Within the fat matrix that forms solid chocolate, some cocoa butter molecules remain in a liquid state. A widely accepted hypothesis suggests that as external temperatures fluctuate, these fat particles migrate to the surface and crystallise into a more stable form—one that is less shiny and appetising.
To study these crystals more thoroughly, Hartel’s lab conducts an “accelerated shelf-life test,” where samples of chocolate are placed in Petri dishes within a chamber and subjected to cycles of varying temperature ranges—typically between 20 and 30 degrees Celsius. While cloudy blooming naturally occurs over extended periods, “we can induce blooming within a month,” he notes, allowing for more detailed investigations into why and how it occurs.
Jiayang Jin, a former student of Hartel now working at the East China University of Science and Technology, is examining how chocolate composition influences fat blooming. In a recent study, she and her team polished the irregular surfaces of sucrose crystals—table sugar—through a step typically avoided in chocolate production: adding moisture to the mixture. They created a white chocolate blend and then added water, which helped smooth out the edges of the sugar molecules. The chocolate was then heated until the moisture evaporated.
Jin’s team discovered that chocolate made with these rounded sugar molecules exhibited slower fat blooming. This suggests that the circular sucrose molecules might pack more tightly together, thereby preventing liquid fat molecules from easily migrating to the surface. “Generally, consumers do not want to see white streaks on their milk or dark chocolate,” remarks Rebecca Kuehn, Research and Development Director at Guittard Chocolate Company. Slowing down fat blooming would extend chocolate’s shelf life, resulting in a more consistent experience for customers and a supply chain with less waste, she adds.
Preventing fat blooming can be achieved through