Thank hybrid yeast for your Easter chocolate feast


Cacao and coffee beans taste different, depending on where they're grown – even if they're the same species. A genetic study found local yeast is behind the diversity of flavours. Amy Middleton reports.


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When you’re devouring the first of your chocolate eggs this weekend, consider how their beans' country of origin may have affected their deliciousness.

A new study, released just in time for this seasonal tradition, offers us sweet-tooths a reason for the taste differences among chocolate and coffee from around the world.

The finding points to the diverse genetics of the yeast that helps ferment cacao and coffee beans. Different types of yeast can be geographically based, and humans have played a big part in this diversification.

Originally, coffee and cacao trees grew in Ethiopia and the Amazon rainforest. They are now widespread around the world, but the yeast involved in the fermentation process varies depending on where the plants are grown.

"Humans have transported and cultivated [chocolate and coffee] plants,” explains Aimée Dudley, co-author of the study at the Pacific Northwest Diabetes Research Institute in Seattle.

“Their associated microbes have arisen from transport and mingling in events that are independent of the transport of the plants themselves."

This process is similar to the diversification of yeasts associated with winemaking. Humans started making wine in the Middle East more than 9,000 years ago, but this spread rapidly. As populations moved and grew grapevines between locations, different strains of yeast were created and combined.

One of the strains is genetically very close to yeast used in winemaking.

To find out whether the same applies for chocolate and coffee, the researchers collected unroasted samples of coffee and cacao beans from different locations around the world, including Central and South America, Africa, Indonesia and the Middle East.

The team then conducted DNA tests on the yeast strains, revealing even greater diversity than among wine yeasts. The findings, published in Current Biology, suggest certain cacao and coffee yeast strains are hybrids, a result of beans being mixed from across the world.

Interestingly, one of the strains is genetically very close to yeast used in winemaking.

"The ancient and continuing global traffic in yeasts associated with wine fermentation may have set the stage for subsequent mingling and admixture events that gave rise to the yeasts that are now associated with the production of coffee and chocolate," explains Dudley.

Because the fermentation process has such a significant impact on the taste of chocolate and coffee, the researchers say identification of yeast strains could have benefits for us consumers.

"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," Dudley says.

In that case, we’ll look forward to future Easter eggs. Thanks, science.

  1. http://www.cell.com/current-biology/fulltext/S0960-9822(16)30064-1
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