Salt: The Only Kind of Rocks Eaten by Humans (Part I)

Salts at Formaggio Kitchen Cambridge

Most folks know that salt is somehow critical to human survival. However, it wasn’t until reading Mark Kurlansky’s book, Salt, that I became aware of just how integral this substance is to the healthy functioning of our bodies and, consequently, the major role it has played in human affairs throughout much of recorded history. As far as our bodies are concerned, the average adult human contains just over a half pound of salt or, as Kurlansky calculates, roughly 3 or 4 salt shakers. However, in the natural course of things, we lose this salt and must take action to replenish it.

Without salt, we get weak, develop headaches, progressing to light-headedness and then to nausea. Ultimately, if deprived long enough, we die. However, we never explicitly crave salt. Before animal husbandry was practiced, humans ate wild animals and were able to get enough salt naturally through this meat. However, once humans began raising animals on farms, the animals were no longer free to roam and find sources of salt for themselves. As animals also require salt in their diets (e.g. a cow needs about 10x the amount of an adult human), early man began to take an interest in sourcing salt directly. It is unclear how we, as humans, first became aware of our salt dependency but it seems that by following the trails of salt-seeking herbivores, early man was able to track down sources of salt, be it in liquid or rock form.

Salt became one of the earliest traded commodities and, for millennia, it remained a major force in international trade. Today, given our knowledge of both chemistry and geology, sourcing salt is no longer as challenging. Straight up salt at the supermarket is pretty cheap and most of us consume way more salt than the minimum our bodies require. That said, not all salts are the same and there is a difference between what one generally finds at the supermarket and naturally harvested salts.

Maldon Salt

Maldon Salt – note the pyramid structure of the crystal.

In her book, CookWise, Shirley Corriher explains what makes table salt and sea salt different. To summarize her excellent description: most table salts are “dense cubes.” In contrast, salts that are harvested from the surface of a body of water (fleur de sel, Maldon, etc.) are four-sided crystals. As moisture evaporates from a salt flat, the salt crystals begin to take shape as hollow squares. This square then sinks a little bit and another slightly smaller, four-sided square grows on top of that. Gradually, a hollow pyramid structure is built.

Corriher relates that the difference between table salt and sea salt is like the “difference between an ice-cube and a snowflake.” According to her research, “about 90 percent of granular salt dropped onto an inclined surface bounces off, while 95 percent of the flaky pyramid form sticks to the surface.” The other main difference between granular table salt and sea salt – the former is almost purely sodium chloride (i.e. salt) whereas the latter contains sodium chloride and other minerals. The variety and quantity of those minerals depends on where the salt is sourced from. Not only does this lead to variations in flavor and appearance but, as Corriher points out, additional minerals helps encourage gluten development in bread baking.

Bread was an important early food staple for humans and salt was important not only for its mineral content but also because it played a critical role in controlling yeast activity. Before the advent of canning and refrigeration, salt was also critical for the preservation of food, another reason why this commodity was a major driver of international trade. Salt is used to cure prosciutto and salami (the former through exterior application, the latter by being mixed into the ground meat), preserved lemons and vegetables and to dry fish, among other foodstuffs. In fact, another book by Mark Kurlanksy, Cod, details how the ability to preserve that fish allowed humans to embark on lengthy sea voyages and explore the world.

In summary – salt is not only critical to our diets but it has played a critical role in our collective history. For more interesting details on the exact extent of its role, definitely check out Mr. Kurlansky’s book – I have only been able to relate a few of the interesting tidbits he was able to uncover. And, stay tuned for my second salt installment as I taste through some of the more unusual salts we have at the shop!


April 8, 2011: For part II of this post, please click here.

  • Scott McKay

    At the risk of sounding like a complete geek, it’s not true that salt is the only mineral that we eat. There are many cultures, mainly in the developing world, where so-called geophagia is common, including, but not limited to, African nations and Haiti. Certain clays are valued for their calcium content, and are used for nutritional purposes as well as to sooth nausea and diarrhea. In Haitian markets, you can buy “bon bons de terre”, which are little clay patties. I’ve also seen clay for sale in the Afro-Caribbean markets in Brixton (London). In fact, any of us can go to the drugstore and get products based on bentonite clay as digestive aids; and Kaopectate is made from a clay called kaolin. Clays are also great at absorbing toxins, so they are used all over for poison control. Again, in the developing world, clay-eating is very common among pregnant women both as a source of calcium, and to calm morning sickness and to absorb environmental toxins.

    I’ve tried bentonite and kaolin myself. They’re not so bad at all!

    • merrybaker

      Hi Scott – Thanks for reading and for your comments. I was not previously aware of the clay-eating traditions you mention so was interested to read your remarks. In response to your point – I did not actually state that salt is the only mineral that we eat, just that it is the only type of rock that we eat. Other minerals that we eat would, I believe, include calcium, iron, zinc and so forth. The rock information I gleaned from Kurlansky’s book where he discusses the “staple food sodium chloride, NaC1, from the only family of rocks eaten by humans.” Clay in geological terms is, from what I can gather, technically a rock though, so given the instances you mention, perhaps this was an oversight on his part? Or, perhaps he meant rocks in the more colloquial sense of stones as opposed to clay?

      • Scott McKay

        Oh, oops, I meant “mineral” in the sense that a geologist would use the term, not a nutritionist. I should have used the word “rock” for consistency. But yes, I think that clay is a rock the same way that salt is a rock. But, as you said, Kurlansky might just be using the word “rock” in yet another way.

  • tryityoumightlikeit

    This was fascinating!
    Congratulations on being featured on FoodPress.

    • merrybaker

      Thanks, Janna! Checked out your blog too – even though you only gave them 3*, I thought the honey Florentines looked great (particularly in the teacup)!

  • kimkiminy

    Great post. I buy my cheese from Venissimo, perhaps you’ve heard of them?
    I have some salt from the Murray River in the Australian Alps. It’s pink, and looks like snowflakes. So, perfect analogy between ice cubes and snowflakes.
    This is the second blog post I’ve seen about “Salt.” I think I must put it on my list!
    I’m currently reading about the Gulag of Soviet Russia. When men escaped, if they had the luxury of taking anything along, salt tablets were one of the best resources they could include.

    • merrybaker

      Thanks, Kim! I will actually be touching on Murray River pink salt in Part II – it’s great stuff and I use it at home for finishing dishes. Re the gulag escapees – I did not know that before but it makes sense, given how important salt is. Very interesting – thank you for sharing!

  • Kathryn Coulibaly

    This was such a cool post and I enjoyed the comments afterwards. I lived in Burkina Faso, West Africa as a Peace Corps Volunteer and I do vaguely remember people consuming clay in some way.

    Thanks for posting!


    • merrybaker

      Thanks, Kathryn! Glad you enjoyed! I took a look at your blog too and particularly enjoyed the Peruvian food post. The photo slideshow was indeed mouth-watering – particularly the lomo saltado over rice!

  • rsmacaalay

    Excellent Info! Thanks for posting

    • merrybaker

      Many thanks, Raymund!

  • overthespoon

    The title of this made me giggle. Very interesting read!

    • merrybaker

      Thank you, Molly! Glad you got a chuckle! :)

      p.s. Your chocolate-covered strawberries look delicious!

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