For chocolate makers, it all starts with the bean. The characteristics of cacao beans used in crafting chocolate play a big role in its flavor profile, which is why chocolate makers look for beans with specific sensory qualities. Chocolate’s natural flavor profiles range from fruity to earthy, but 100% chocolate is naturally bitter.
Once cacao beans have been processed, there’s not a lot a chocolate maker can do to change a product’s flavor profile beyond adding ingredients like sugar to sweeten it and cut the bitterness.
“You carefully source your beans, depending on where you want to have them from and what you are looking for in your product, and then you can roast them, and then you can add different ingredients,” says Helene Hopfer, an assistant professor in the Department of Food Science at Pennsylvania State University. “But that’s really all you can do to change the sensory properties of your product.”
Hopfer and her fellow researchers wanted to find out if there are roasting parameters that can reduce chocolate’s bitterness and to explore how tasters respond to various levels of bitterness. The bitterness in chocolate likely comes from methylxanthine alkaloids, including caffeine and some flavonoids. The cacao varietal, the terroir, the ripeness of the beans at harvest, and processing can influence these compounds.
The researchers chose fermented and dried cacao from Ghana, Peru, and Madagascar because they represent very different origins, says Hopfer, co-author of a research paper on the findings that was recently published in Current Research in Food Science. Cacao from Ghana is a good example of traditional cacao from West Africa, which typically has lots of chocolate notes, she says, while cacao from Madagascar and Peru would be classified as specialty cacao. “Craft chocolate makers are really trying to highlight the country of origin of different cacao beans,” she points out.
For the first part of the study, the samples were roasted in a forced air convection laboratory oven at a range of 24˚C to 171˚C for up to 80 minutes. A control sample was left unroasted. After roasting, the samples were made into a chocolate liquor within 2 days. In the second part of the study, the researchers provided 27 chocolate liquor samples covering all three origins to 145 tasters, who sampled them over a span of 5 days.
What they found was that prolonged roasting at higher temperatures improved the tasters’ responses; temperature played a more important role than time. The optimal temperature and time combinations for bitterness reduction were 171˚C for 20 minutes, 151˚C for 54 minutes, and 135˚C for 80 minutes.
Unsurprisingly, says Hopfer, liking was inversely correlated to the intensity of the bitterness of the samples. The Ghana liquor samples won the highest marks from the study’s tasters by a significant margin, and that chocolate naturally has the lowest bitterness levels of all the regions. The Peruvian is the most bitter and was the least preferred. But it’s interesting, Hopfer notes, that although the different regional cacao samples have different levels of bitterness, roasting methods can reduce bitterness to some degree for all of them.
“Origins seem to have a really big effect on bitterness in general,” says Hopfer. “You can’t really move one origin completely to lower levels [of bitterness] compared to other origins but optimizing roasting can definitely decrease bitterness and increase liking.”
The team is now researching the ways in which postharvest processing—fermentation, roasting, and drying—may affect cacao’s sensory properties. “We’re trying to understand the different processing steps and their effect on the final product outcome and the nutritional content, the health benefits, and the sensory properties of these chocolates, depending on how they are processed,” says Hopfer.