Field of Science

All natural, locally sourced liquid nitrogen?

Robyn Sue Fisher wants you to know that she would never cook with chemicals not found in nature. Smitten, her ice cream shop in San Francisco’s Hayes Valley, may at moments resemble a high school chemistry lab, but that’s because Fisher uses liquid nitrogen to freeze her product.
Nitrogen is “a natural element,” she notes. “It’s all around us.” [The original lead to this NPR blog post.]

I imagine not a few chemists reading this want Robyn Sue Fisher to know that liquid nitrogen is not found in nature on this planet. I suspect if she posted this photo of a cryogenic nitrogen plant in the ice cream shop, she'd have a hard time convincing her customers that liquid nitrogen was natural.

Her comments beg the question of what constitutes a chemical in the mind of a non-chemist.   If we take IUPAC's Gold Book as the arbiter of the technical definition,  a chemical is a material of "constant composition best characterized by the entities (molecules, formula units, atoms) it is composed of." Everyday language has drifted from the technical.  The Oxford English Dictionary offers this definition for the non-technical speaker: "a distinct compound or substance, especially one which has been artificially prepared or purified."

Most people would agree that in common usage chemical carries the connotation of both artificial and noxious, while chemists attach no such presumptions as to source or toxicity to the term.  Much as chemists wish it were not so, there is a growing language gap, and I think it unlikely we are going to regain the ground lost.  Molecule still comes across as more neutral in tone to a non-chemist.   So we are in a moment where we have people who are aghast at chemicals in their food, and others who are fascinated by molecular gastronomy (and likely some overlap in that population).

In principle, I do like the idea of locally sourced ingredients, maybe I should start my own shop and advertise that I use only locally sourced, artisanally produced liquid nitrogen?

I have to say I was also fascinated with how the NPR post morphed throughout the day in response to the comments on the blog.  By the end of the day the introduction read:

Robyn Sue Fisher's ice cream shop, Smitten, in San Francisco's Hayes Valley, may at moments resemble a high school chemistry lab, but that's because Fisher uses liquid nitrogen to freeze her product. 
Nitrogen is "a natural element," she notes. "It's all around us."
Andrew Bissette has a good piece about chemophobia on Carmen Drahl's blog Grand CENtral today  (In Defense of Chemophobia) which, along with this post from 2011 by Sciencegeist touch on the language issue.

(H/T to Fran who sent me the link to the original NPR post) 


  1. I suspect that Robyn Sue Fisher is referring to the material, not its state. Her claim is still valid as far as I am concerned.


    A Chemist

  2. It depends a bit on the context, whether she meant simply to explain that nitrogen is an element found in the environment, or whether the listener is meant to extrapolate from this statement that liquid nitrogen is safe. Since she could make the same claim and cook with arsenic, the purpose of the statement is rhetorically cloudy, I would agree, but I think most non-chemists would equate "natural" with "safe"

    And as chemists we know that states matter, mercury vapor has hazards that mercury liquid does not.


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