If you're looking for the secret to the best tasting chocolate, science may have found the answer for you.
Previous studies discovered that the yeasts used to ferment cocoa during chocolate production can modify the aroma of the resulting chocolate.
Wild strains of yeast are also found in the natural fermentations that are essential for chocolate and coffee production.
Now scientists in Seattle, Washington, believe their latest research could dramatically improve the taste and quality of chocolate.
Their new genetic evidence reveals the yeasts associated with coffee and cacao beans have had a rather unique history.
In comparison with the yeasts found in vineyards in New Zealand and the rest of the world, the new work shows that those associated with coffee and cacao beans show much greater diversity.
"Our study suggests a complex interplay between human activity and microbes involved in the production of coffee and chocolate," says Aimee Dudley of the Pacific Northwest Diabetes Research Institute in Seattle.
"Humans have transported and cultivated the plants, but at least for one important species, their associated microbes have arisen from transport and mingling in events that are independent of the transport of the plant themselves."
Coffee and cacao trees originally grew in Ethiopia and the Amazon rainforest, they are now widely cultivated across the "bean belt" that surrounds the equator.
After they are picked, both cacao and coffee are fermented for a period of days to break down the surrounding pulp.
This microbe-driven process also has an important influence on the character and flavour of the beans.
Dudley and her colleagues wanted to know where the yeasts in these human-associated fermentations came from.
Had coffee or cacao-specific yeast strains been unknowingly transported along with the plants? Or, do particular regions of the world harbour novel yeast populations?
To find out, the researchers bought unroasted coffee and cacao beans grown in Central and South America, Africa, Indonesia and the Middle East and isolated the associated yeast in their Seattle laboratory.
Genetic analysis of those yeast strains revealed that yeasts from coffee and cacao beans were substantially more diverse than the wine yeasts.
Interestingly, the genetic signatures of the yeast strains strongly clustered according to the geographic origin of the beans.
In fact, Dudley says, this association was so strong that they were able to accurately determine the origin of the beans solely from the DNA sequences of their associated yeasts.
The findings show that the yeast strains associated with coffee and cacao have multiple, independent origins.
In other words, not all cacao strains are related, nor are all coffee strains.
What's more, the yeast strains associated with coffee or cacao in specific places appears to be hybrids that resulted from the mixing of strains from different parts of the world.
In fact, one of those strains is closely related to the yeast used to make wine.
"The ancient and continuing global traffic in yeasts associated with wine fermentation may have set the stage for subsequent mingling and admixture events that give rise to the yeasts that are now associated with the production of coffee and chocolate," Dudley added.
The researchers say the findings could lead to improvement in chocolate and coffee. Studies of wine production have shown that they yeasts associated with wine fermentation significantly influence the properties of the wine, including its flavour and aroma.
"Given that the yeast strains associated with coffee and cacao fermentations are substantially more genetically diverse than the wine strains, they could play an even larger role in the properties of coffee and cacao produced in different regions of the globe."
Professor Richard Gardner of The University of Auckland explained that the fermentation process is very important in the final chocolate flavour and research on this topic is invaluable.
"Up until now chocolate has been produced using whatever yeast are in the beans, this is what used to be the case with wine up until about the 1980s, when specific starter strains started to be produced and used by the industry.
"But it seems likely that, as we understand the chocolate production process better, it should be possible to develop specific and improved strains of yeast, perhaps bacteria, that can act as starters to make a wider range of different chocolates with different flavours.
"Having a wide range of different yeast types is essential for this to occur."