Catching Fake Honey: The Chemistry of a Global Fraud Problem

Honey is one of the most commonly faked foods sold worldwide. Dishonest producers stretch real honey by mixing in cheap sugar syrups made from corn or sugarcane. Sometimes they cut costs so aggressively that a jar labeled "pure honey" contains only a small amount of real nectar-derived sugar. One common method for catching this fraud relies on an unlikely source of evidence: the way different plants absorb carbon dioxide during photosynthesis. Most flowering plants that bees visit for nectar use what is called the C3 photosynthetic pathway. This process leaves a distinctive ratio of carbon isotopes in the sugars the plants produce. Corn and sugarcane use a different pathway, called C4 photosynthesis. This process produces sugars with a measurably different isotope ratio. Genuine honey should carry only the C3 signature from nectar plants. A lab technique called carbon isotope ratio analysis can detect even small amounts of added corn or cane syrup. It does this by measuring how far a honey sample's isotope ratio has shifted toward the C4 signature. This method does have real limits. It struggles to detect syrups made from other C3 crops, such as rice or beets, because those share honey's own isotope signature. For this reason, investigators increasingly combine isotope testing with newer chemical techniques to catch more sophisticated fraud.