The most popular beers in the world are lager beers, think Budweiser and Coors. Now, 500 years after German monks first brewed lager beer scientists have discovered the origin of a key ingredient. Researchers at the CU School of Medicine traced a strain of yeast, used in lager brewing, back to South America. Zachary Barr talked about the research, and its larger implications, with Mark Johnston, who chairs the Department of Biochemistry and Molecular Genetics. (Originally aired Aug. 30, 2011)

[Photo: Megan Verlee]