Carbon isotope evaluation of the claims in MillerCoors vs Anheuser-Busch

MillerCoors (MC) sued Anheuser-Busch (AB) over a 2019 advertising campaign emphasizing that Miller Lite and Coors Light beers are made with corn syrup. Because plants using the C4 photosynthetic pathway (corn, sugar cane, millet) are isotopically enriched in ¹³C, relative to ¹²C, in plants that use the C3 pathway (rice, barley, rye, wheat), carbon isotopes can provide relevant evidence. The plaintiff, MC, asserted 1) there is no corn syrup in the final product of Miller Lite or Coors Light; 2) they never use high fructose corn syrup (HFCS); 3) AB uses corn syrup as a fermentation aid in other products; and 4) AB adds HFCS to other product lines. I measured δ ¹³C_VPDB values for 27 beers, including the eight best-selling U.S. beers covering > 50% of the U.S. market. Miller Lite (−24.6 ‰) and Coors Light (−24.5 ‰) had 0–15% carbon from C4 sources, while Bud Light (−27.3 ‰), an AB product, had little to no C4 carbon. However, other AB products use more C4 carbon sources, including Bud Light Platinum (−22.0 ‰, 27 ±5% C4), Natural Light (−22.1 ‰, 26 ±5% C4), Category 5 Malt Hurricane (−21.1 ‰, 33 ±5% C4), Rolling Rock Extra Pale (−20.7 ‰, 37 ±5% C4), and Lime-A-Rita (−11.9 ‰, 98 ±4% C4). Corn syrup and HFCS were isotopically indistinguishable. This study supports claim 3, but cannot address claims 1, 2, and 4, highlighting both the utility and limitations of δ ¹³C measurements in ingredient identification in a civil case.