Sweet, salty, sour, bitter, umami and — ammonium? Scientists discover potential sixth basic taste

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You either love it or you hate it. With salty licorice, it seems there is no middle ground. The ammonium hit is unmistakable and, as it turns out, the flavour profile of this divisive candy (a.k.a. salmiakki in Finnish) could be the key to something bigger. A team of neuroscientists at the University of Southern California and the University of Colorado have discovered that ammonium chloride — the key ingredient in the Scandinavian confection — may qualify as the sixth basic taste.

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Scientists have long known that the tongue responds strongly to ammonium chloride, the researchers said. Outside of what Jukka Annala, a Helsinki-based author and chairman of the Finnish Salty Liquorice Association, calls the “salty-licorice countries” (Sweden, Norway, Denmark, Iceland, Finland, the Netherlands and the northern part of Germany), this response can be very powerful indeed.

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Writing for Saveur magazine in 2017, writer Andrew Richdale described his first taste of salmiakki as “simultaneously fascinating and … abusive? Or at least odd, like a knocked funny bone.”

Annala, on the other hand, appreciates it so much, popping a pastille is a daily occurrence. “It’s a sinful combination of salt and sweet, which makes it so exciting,” he said on Gastropod.

As Annala explained on the podcast, ammonium chloride is used as an expectorant in cough medicine. Someone combined it with licorice — commonly for sale at pharmacies — and started making salmiakki lozenges and syrups. What started in the pharmacy is now one of Northern Europe’s favourite candies.

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To be considered a basic taste — like sweet, salty, sour, bitter and umami — a flavour’s chemical signature must trigger specific receptors on the tongue, according to NPR. Until now, scientists didn’t know which receptors were responsible for that forceful ammonium chloride response.

In research published in Nature Communications, University of Southern California neuroscientist Emily Liman and her team found that ammonium chloride — the key ingredient in salmiakki, giving it its saltiness — activates the same protein receptor that signals sourness (OTOP1).

“Ammonium is somewhat toxic,” Liman said in a statement, “so it makes sense we evolved taste mechanisms to detect it.”

This isn’t the first time scientists have uncovered a potential sixth taste. In September 2015, as NPR reported, a study published in the journal Chemical Senses made the case for oleogustus (Latin for “a taste for fat”). Seven months before that, in the journal Flavour, Australian researchers argued that “the next five to ten years should reveal, conclusively, whether fat can be classified as the sixth taste.”

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Whether oleogustus or ammonium chloride end up qualifying as the official sixth taste remains to be seen. It took the scientific community more than 80 years to arrive at the same conclusion as Japanese chemist Kikunae Ikeda, who identified umami as the fifth basic taste in the early 1900s.

In the meantime, Liman and her team plan to continue their examination of the OTOP1 receptor’s response to ammonium chloride and hope to gain insight into its evolutionary significance.

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