Bad perfume: Cardboard’s intense scents

Wet cardboard and food should not share the same air space

We often joke about food that lacks any perceptible flavor as tasting like cardboard. In fact, cardboard’s blandness is one facet of its appeal to the food industry. Manufacturers pack foods in cardboard and pizzeria’s deliver their cheese-topped pies in it precisely because it won’t affect the flavor of their products. Or at least that’s been the presumption.

A pair of researchers in Germany has now catalogued 37 smelly compounds emitted by cardboard — chemicals that they argue could indeed temper the flavor and scent of foods. “Most of the identified compounds were described as odor-active [i.e. smelly] cardboard constituents for the first time,” report Michael Czerny of the Fraunhofer Institute for Process Engineering and Packaging in Freising and Andrea Buettner of University Erlangen-Nuernberg.

They found some of these compounds present in relatively high amounts, although their predominantly woody/musty notes tended to remain below the radar screen until cardboard got wet — as might occur if your pizza was delivered on a rainy night, or a food warehouse was not humidity controlled.

Indeed, “The aroma profile changed drastically when the cardboard was moistened,” becoming “intense” and yucky — as in woody and musty with very pronounced fatty and moldy highlights, Czerny and Buettner report in an upcoming issue of the Journal of Agricultural and Food Chemistry.

Contributing to the overall off-putting smell were the leathery-inky scents of 3-propylphenol and 3-methyphenol. Another 29-letter-long compound smelled metallic and benzothiazole imparted the smell of rubber or car tires. Yum.

And it gets better. Czerny and Buettner describe two constituents of cardboard’s scent — 4-methylphenol and 4-ethylphenol — as having a “horse stable-like, fecal” smell. Other off-gassed chemicals smelled: “cheesy, sweaty;” soapy, fatty, mushroomlike, citrusy, spicy, woody or coconutty. A compound known as 2-methoxyphenol seemed to have a particularly complex scent — at once smoky, vanillalike and sweet.

The chemists aren’t sure why most of these chemicals don’t assault our noses while the cardboard remains dry, but speculate that some might remain walled off in cellulose until contacted by water — “which acts like a solvent.”

In a followup experiment, the pair showed cardboard’s off-scents could transfer to salad oil, presumably a substance meant to model fatty foods.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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