Unexpected Sources: Your "Safer" Glass Bottle Might Not Be

Author

Sam Garcia
September 10, 2025

A recent study by France's food safety agency, ANSES, has revealed that beverages sold in glass bottles surprisingly contain significantly more microplastic particles than those in plastic bottles or metal cans. The findings, published in the Journal of Food Composition and Analysis, challenge previous assumptions about packaging safety.

The study, which aimed to investigate the quantity of microplastics in various drinks sold in France and assess the impact of different containers, found an average of approximately 100 microplastic particles per liter in glass bottles of soft drinks, lemonade, iced tea, and beer. This amount was five to 50 times higher than the levels detected in plastic bottles or cans.

Researchers, including PhD student Iseline Chaib who conducted the research, expressed surprise at the results, having initially expected the opposite. The primary source of this contamination was identified not as the glass itself, but as the plastic-based paint coating on the outside of the metal caps used to seal the glass bottles. Tiny scratches, likely caused by friction between caps during storage, are believed to release these paint particles into the beverages.

Specific findings from the study indicate that while water generally contained lower levels of microplastics across all packaging types (around 4.5 particles per liter in glass bottles and 1.6 in plastic), other beverages showed higher counts. Soft drinks averaged about 30 microplastics per liter, lemonade 40, and beer around 60 to 83 particles per liter in glass bottles, with some small glass bottles of beer peaking at 133 MPs/L. Interestingly, wine contained few microplastics, even in glass bottles with caps, a discrepancy for which the reason remains to be fully explained, though it could be related to wine bottles often being sealed with corks or synthetic stoppers rather than metal caps.

While there is currently no established reference level for a potentially toxic amount of microplastics, making it impossible to definitively state whether these figures represent a health risk, ANSES suggested that drink manufacturers could easily reduce the amount of microplastics shed by bottle caps. A cleaning method involving blowing the caps with air, then rinsing them with water and alcohol, was shown to reduce contamination by 60 percent. Manufacturers could also consider changing cap storage conditions to avoid friction or modifying the paint composition. This study highlights an unexpected source of microplastic contamination that the beverage industry can address.

Detailed Breakdown of Findings:

  • Unexpected Results: Researchers, including PhD student Iseline Chaib, anticipated the opposite outcome, expecting plastic bottles to have higher microplastic contamination.

  • Primary Source of Contamination: The microplastics in glass bottles were primarily traced to the plastic-based paint coating on the exterior of metal bottle caps, not the glass itself.

  • Mechanism of Release: Tiny, invisible scratches on the cap's paint, likely caused by friction during storage, are believed to release these particles. These particles then fall into the drink when the bottle is sealed or opened.

  • Higher Microplastic Concentrations: Glass bottles of soft drinks, iced tea, lemonade, and beer contained an average of approximately 100 microplastic particles per liter. This amount was between five and 50 times higher than the levels found in plastic bottles or metal cans for the same beverages.

  • Specific Beverage Contamination Levels:

    • Cola, iced tea, lemonade, and beer in glass bottles showed significantly more microplastics, in some cases nearly 50 times more than in plastic bottles and cans.

    • Soft drinks averaged 30 microplastics per liter, lemonade 40 per liter, and beer around 60 per liter in glass bottles. Some beers in small glass bottles peaked at 133 microplastics per liter.

  • Lower Contamination in Water and Wine: Water, both still and sparkling, had relatively low microplastic content across all packaging types, with glass bottles of water containing slightly higher levels (4.5 particles per liter) compared to plastic (1.6 particles per liter). Wine also contained few microplastics, even in glass bottles with caps, possibly due to the use of corks or synthetic stoppers instead of metal caps.

  • Health Implications (Ongoing Research): While microplastics are pervasive in our environment and have been linked to health issues such as inflammation, oxidative stress, gut issues, infertility, hormone disruptions, cardiovascular disease, and cancer, there is currently no direct evidence that the amount of plastic found in these beverages is harmful to human health. Research into the health effects of microplastics is ongoing, and there is no established reference level for a potentially toxic amount.

  • Recommendations for Manufacturers: Researchers and experts suggest that beverage manufacturers can easily reduce microplastic contamination by revising their bottle caps and implementing cleaning processes. A simple solution tested involved cleaning caps with a blast of air and then rinsing them with water and alcohol before bottling, which reduced contamination by 60 percent.

  • Study Origin: The research was conducted by French researchers from the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) and involved examining various beverages sold in France.

  • Microplastic Definition: Microplastics are tiny pieces of plastic less than 5 millimeters long.

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