The Chemistry of Popcorn

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Today (19th January) is apparently National Popcorn Day, so what better time to look at the chemistry behind it? This graphic takes a brief look at some of the compounds that give popcorn its flavour and aroma, as well as what makes it pop!

There haven’t been a great number of studies on the chemicals that make up the aroma and flavour of popcorn. The first of these, way back in 1970, identified a range of compounds, and made some general suggestions as to which ones were important for flavour. Compounds called pyrazines contribute nutty flavours, with 2-acetylpyrazine, whose aroma is itself described as ‘popcorn-like’, cited as a key odorant.

Later studies looked in more detail at the contributing compounds. They found that although 2-acetylpyrazine is present, it isn’t one of the more significant contributors to aroma. Though many compounds make a degree of contribution, the three key compounds identified were: 2-acetyl-1-pyrroline, with a roasty, popcorn-like aroma; (E,E)-2,4-decadienal, with a fatty, fried aroma; and 2-furfurylthiol, which in isolation has a roasted coffee-like aroma. A number of other pyrazine, pyridine, phenol, and aldehyde compounds make more minor contributions.

Flavourings can also add their compounds to the mix. 2,3-butanedione (commonly known as diacetyl) is one such compound, which was used in butter flavourings. Its use in these flavourings has declined due to concern regarding workers preparing the flavourings inhaling the compound. Inhalation of diacetyl can cause inflammation of the bronchioles in the lungs, a condition sometimes referred to as ‘popcorn lung’.

Popcorn lung is not a significant concern for consumers, as they are unlikely to be inhaling large amounts of the compound, though there have been isolated cases of people preparing popcorn in large quantities on a regular basis showing symptoms. Diacetyl is less frequently used as a flavouring now, though its substitute, 2,3-pentanedione, has also been linked with the condition in workers.

There’s also some chemistry behind the cooking process of popcorn. Popcorn kernels contain around 14% water by mass. As they are heated, this water vaporises; however, it remains trapped inside the kernel, and so the continued heating raises the pressure inside the kernel’s shell. Eventually, usually at around 180˚C, the kernel’s shell will crack, and the corn will pop.

The popping noise that accompanies this is not, as might be expected, the sound of the kernel’s shell cracking, but rather a consequence of the release of the pressurised water vapour. As it’s released, the cavity inside the kernel acts as an ‘acoustic resonator’, which is what amplifies the sound of the pop and makes it audible. During heating, the starch inside the kernel becomes molten, and when the kernel pops it quickly escapes, rapidly cooling and forming popcorn’s characteristic fluffy shape as it solidifies.

 

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References & Further Reading