The common filler ingredients that have been found include wheat, husks and sticks, soybean, acai seeds, barley, corn, rye and brown sugar—even clumps of earth.
These extra and surprising impurities in coffee aren't supposed to be harmful, although it's not clear what health consequences they could have for people with celiac disease, who can't eat gluten—as well as those with gluten sensitivities and food allergy issues.
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One thing is for sure: With such counterfeit coffee, producers are hoping to stretch their coffee supplies and increase profits, especially as a global shortage looms in the next few decades, which many blame on climate change.
Production from Brazil, the top country producer of coffee, is projected to drop in 2014 due to the recent drought there.
"With a lower supply of coffee in the market, prices rise and that favors fraud because of the economic gain," said research team leader Suzana Lucy Nixdorf in the study. Nixford and her research team are developing a test at the manufacturing level to quickly find unwanted fillers in coffee before the beverage reaches stores and restaurants.