Cooking with Njall: Salt Burning, Take Two

A while back, I discussed a failed experiment in Viking-era salt production. The idea was to burn some Icelandic kelp, and use the residue as a “salt” of a sort. It didn’t really seem to do anything, and so I moved on.

But I’ve never been the type to just leave something alone. I’m a scientist, after all – I can’t accept that something is a bad idea until I’ve done it at least 5 times.

Rigor is very important.

I’ve had the remnants of my experiment kicking around in a Mason jar for a while now, so I figured what the hell – let’s give this another go. Refine the technique and try something new.

Salt Experiment Redux 1

I promise I am not making explosives.

We were recently down in North Carolina visiting some of my fiancee’s friends (fellow SCA types), and Solvarr gave me a fantastic idea: do a water extraction of the charred crap, and boil that.

In the picture above, I’ve mixed 50 g of charred kelp with 100 g of water, and allowed it to steep for ~30 minutes. The idea is to attempt to extract the salts from the solid phase, separate the liquid, and boil it down to solids.

This seems like something that may have plausibly been done in the Viking era, albeit with fairly different equipment. Recall the various bits of language revolving around “salt” in Old Norse: salt-brenna (“salt-burning”), salt-fjara (“salt-beach”), and salt-ketill (“salt-kettle”). We also see words referring to two different colors of salt: hvíta-salt (“white salt”) and svarta-salt (“black salt”).

The “salt-ketill” was something I hadn’t explored before, but it makes some sense. Ash or char the kelp in a kettle (potash anyone?), mix it with water, strain out the solids (maybe with an open-weave cloth of some kind), and boil the hell out of it. Pliny makes mention of boiling seawater, and this technique is also alluded to later by Olaus Magnus, so there seems to be precedent for the generation of salt by boiling water. Adding kelp ashes would effectively increase the solute concentration, which would in turn improve yield (making better use of precious fuel).

A relatively recent excavation of a Viking-age house in Iceland (paper courtesy of Hrefna) shows an area of high salt concentration in the house. The authors suggest it to be an area used to store kelp ash – they suggest for wool dying, but of course, they could have other uses. It does show that Vikings may have generated and stored ashed and/or charred sea plants for various uses – so mixing some with water to boil into salt seems completely feasible.

Salt Experiment Redux 2

Continuing the fine tradition of putting weird things in my mouth.

After steeping, I strained the stuff through a coffee filter and squeezed the crap out of it. All in all, it generated 42 grams of the above-pictured black liquid. I lack proper volumetric measuring equipment, so I can’t effectively estimate the density of the liquid. No matter – I’m going to boil the crap away and weigh the solids. Into the pan it went, and onto the stove:

Salt Experiment Redux 3

I’m pretty sure I belong on a watch list somewhere.
Still not making explosives.

Holy crap, it worked! I got…stuff! Stuck to my pan! My fancy copper-core frying pan that cost more than I’d like to admit!

Note to self: in the future, use a cheaper pan.

This process didn’t smell nearly as badly as the initial charring experiment did. There was something of an off odor, but that was mostly due to dirty electric stove coils – though there was a hint of kelp in the air.

I scraped the solid crap into a bowl for display purposes. It was a mostly-dry salt, with a bit of residual moisture (think fleur de sel or other hand-harvested sea salt) and a variety of colors. There was some fine grey ash mixed in as well, indicating a fairly complete combustion. We likely did completely combust the kelp during the charring – we just couldn’t separate the ash from the remnant matrix.

Salt Experiment Redux 4

Right? Almost like I planned for this to happen.

After all was said and done, I had ~5 grams of that stuff up above left. So from 150 grams (50 grams kelp/100 grams water) to 42 grams liquid to 5 grams solid. Given that the kelp meal itself is 10% salt by weight, this seems like a pretty efficient extraction method! 50 grams go in, 5 grams come out. Not too shabby, doubly considering the small quantities in use.

As is tradition, the ultimate test lay in putting that shit in my mouth.

My friends, I made salt.

There’s a hint of kelp and something burned, but no real grit. Fairly crystalline texture and appearance. Very salty. Complex tasting, too – like an interesting sea salt. No funky aroma – just a hint of burnt nothingness.

It worked. Kelp ashes + water + fire = salt.

This is not the only method I tried tonight: I also attempted a different manner of direct-fire burning. I’d bought some metal mesh screen material, and this time tried building a fire underneath the charred kelp, figuring that increased oxygen flow would do the trick.


Salt Experiment Redux 5

Also not making drugs. Or explosives.
Or salt.

I tried several configurations (the tin can there was used as a chimney starter and to try to contain the heat), but to no avail. I got the damn stuff glowing like charcoal, gave it lots of oxygen, stirred it around, left it alone, dumped lighter fluid on it – nothing.

Charred kelp meal is evidently the most flame-retardant substance known to man.

This is probably a byproduct of the configuration of the kelp – it just will not conduct oxygen and heat in such a way as to promote combustion. I’m sure that sheet kelp would actually combust like fuel – but they may very well have still mixed the ashes with water to produce the salt, as that is a good way to separate the gritty crap from the useful salt.

So my proposed method for salt production involves:

1) Charring or ashing kelp

2) Mixing that product with water

3) Separating the solids

4) Boiling the remaining liquid until only a residue remains

I have yet to experiment with actually using the stuff like salt – but at least now I have a process that will allow me to get rid of my remaining 50 pounds of kelp meal!

Future experiments will involves meat curing and fish salting using this product, to see what properties it would impart on the food. Salt is, after all, fairly fundamental in food chemistry, and the exact type of salt used can radically alter a product.

Different kettle materials can also affect the product. Iron pots, for example, will leach iron into the final salt – affecting the chemistry and flavor of any food made with it, and the diet of those who ate it.


Of course, this all assumes that they were even using salt for food preservation. A redditor from the Faroe islands posted some pictures of traditional Faroese fermented lamb (skerpikjøt, which literally means “sharp meat”) over in /r/meat:

Fuck it, you win.

They slaughter the lambs in October, hang them up in a shed for a couple of months, and then eat them. Mind you, the average temperature in the Faroes at this time ranges from 4 – 8 C, so the whole place is basically a giant refrigerator. No salt, just the breeze from the North Sea blowing through the shed constantly. Air-dried and mold-covered. And they eat the stuff raw, like prosciutto but with more microbial action. It also has a very very strong gamey flavor.

My ancestors ate some weird shit, man.

Hell, they still do.

So that’s what’s in store for this series: weird-ass foods, which will eventually be coupled with weird-ass beers.

You know you love it.

4 comments on “Cooking with Njall: Salt Burning, Take Two

  1. Cteavin says:

    Wow. That was informative, well written, and opened my eyes to something new — thank you.

  2. Kythe says:

    So, here’s a question: Why would they go to all this work instead of just evaporating sea water for the salt? Does the kelp instill something that regular sea salt doesnt?

    • An excellent question!

      I haven’t performed a full mineral analysis on the resultant salt, but it should contain several other minerals and compounds that pure seawater salt would not.

      I performed an experiment in the lab to see if this whole process actually does anything of value. I made 10% solutions of both the regular charred kelp and the extracted salt, using distilled water. Measured the conductivity of the solutions and converted to total dissolved solids (TDS).

      The charred kelp resulted in a solution of 3.99% TDS, and the “salt” created a solution of 7.55% TDS. This indicates that the water extraction of charred kelp results in an increased concentration of soluble material in the resultant “salt” – or in other words, it serves to effectively separate the salts from the kelp.

      This also means you could start with plain seawater, soak the charred kelp in it, boil down the resultant liquid, and wind up with a larger yield of purer salt. Regular seawater is 3.5% salt (w/v), but this method could increase the salt concentration in that water – yielding more mineral salt when it’s done.

      You’d do it because it makes more efficient use of the fuel used to make salt.

      Hypothetically, anyhow.

  3. […] by thedraughtsaredeep As you will remember, I’ve been screwing around with Viking-era salt production methodology. Based on a review of […]

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