Substitute for saltpetre

Question

I was reading a recipe for Okra Soup with Goat Meat and was surprised to find "saltpetre" on the ingredient list, with no quantity listed. Having never seen this as an ingredient in anything other than gunpowder, I did a little research to try and figure out what was going on.

According to Wikipedia, it is:

widely used as a thickening agent in soups and stews such as okra soup and isi ewu. It is also used to soften food and reduce cooking time when boiling beans and tough meat.

This makes sense to me because the recipe I'm looking at is West African (Ghanaian), though the author of the recipe talks about using it to make the okra more "slimy", which I'm less sure about.

What concerned me is that the sites selling spices which had this available were plastered with warning that this needs to be carefully measured to the gram, and care must be taken to consume only safe amounts. (Example: "This ingredient must be measured with a gram scale and used with extreme caution.")

So now that I've succeeded in scaring myself out of using this ingredient – what can I substitute for the saltpetre in a Ghanaian-style okra stew? Will salt plus a thickener, such as a roux or cornstarch, achieve the same effect? And should it be added later than the saltpetre was, which was with the okra in the initial boil?

(And if anyone can shed light on what effect it might have on the okra's "sliminess", I would appreciate that – I've never heard of people trying to make boiled okra more slimy as this recipe implies!)

Answer 1

The short answer for your substitution question is -- add some baking soda, i.e., sodium bicarbonate.

How much? I don't know, as the recipe doesn't even give a hint. Start out with a little -- maybe a half-teaspoon? You can always add more, but it can give an unpleasant aftertaste. With a little bit of baking soda, producing an alkaline solution, the okra will get a bit more green and the meat may be slightly tenderized. As you increase the concentration of baking soda, the okra will likely get mushy and "slimy." Baking soda often is described as giving a "soapy" consistency to food when used in excess.

As to the bit about "saltpetre," it's almost certainly a mistranslation (apparently a very common one in West Africa).

This was quite an interesting business to sort out. I'm no expert in the cuisine of Ghana or West Africa, so if anything I will say here looks wrong to someone with first-hand knowledge, please correct me.

If you care about the logic and sources I'm using to justify all of this, details are below.

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My guess is that the confusion came out of the fact that these West African salts are often known in English as "potash." Another traditional name for "saltpetre" is "nitrate of potash," which would be the old name for potassium nitrate (itself often a component of "potash" when used as fertilizer). While these salts are very common in West Africa and are known in English as either "potash" or "saltpetre," the largest composition is generally sodium (bi)carbonate and/or potassium (bi)carbonate. There's no potassium nitrate involved at all. As you rightly identified, potassium nitrate is a curing salt, which needs to be used in precise quantities, generally to preserve meat.

Potassium nitrate, however, is NOT generally known for making vegetables "slimy," nor (as the Wikipedia page claims) for reducing bean cooking time or to soften tough meat. I was suspicious of the Wikipedia claim and tracked it back to its first appearance in the article in 2012, and it's never really been properly sourced. A quick search of Google Books demonstrates that most of these claims similar to Wikipedia only appear in books and sources since 2012, probably imitating the Wikipedia article.

(I'm sure I've gone on about this before, but never believe anything on Wikipedia unless you've followed the sources and verified. It's a great resource, but information must be verified and properly sourced, as anyone can edit it.)

Furthermore, an alkaline tenderizing agent like sodium (and/or potassium) carbonate or bicarbonate immediately occurred to me as better fitting the culinary description from Wikipedia. For example, baking soda is well-known to speed the cooking of beans.

Anyhow, what we're really talking about here is a "salt" that is used in West Africa, which is not sodium chloride. It goes under a lot of different regional names: kanwe, kanwa, akanwu, kuan, natron, trona, nikkih, kilbu, sel gemme, and limestone are a few, in addition to potash and (quite inaccurately) saltpetre. Traditionally, it is often a harvested "salt" from regional lake deposits, but there are a variety of other preparations and methods for making it, depending on the country/region.

So, how do I know the Wikipedia article is wrong and what is requested in this recipe? Well, first let's begin with a study done in Ghana itself by USAID, which mentions this specific dish on page 38:

Fresh okro soup: Prepared similar to light soup but with added chopped boiled okro with kanwe (saltpeter).

Here we have confirmation that the local name for this salt is "kanwe," but it is also referenced as "saltpeter."

Later in this study (p. 167), we are told that "saltpeter" is "kanwa" and that it speeds up the cooking of beans (just as the Wikipedia article tells us).

Beans are an important part of the IYC diet and mothers use sal[t]petre (kanwa) to speed the cooking process. It is not known whether saltpeter has any adverse health effects and this needs to be investigated.

So, we're looking for kanwa/kanwe. And aside from Wikipedia and a few sources that seem to mimic that source since 2012, I haven't found any sources that connect this to potassium nitrate. Most commonly, despite the misnomer of "saltpetre," academia studies that have analyzed such salts have found they contain "potash" instead, or potassium (bi)carbonate.

(Technical note: the carbonates of sodium and potassium have similar chemical properties to the bicarbonates but are stronger, i.e., have a more alkaline effect. They'll also do similar things to food.)

For confirmation of what "kanwa" is, we can look to this article:

Sariem et al., “Acute toxicity studies and characterisation of local dietary salts in Nigeria” (2016)

Local dietary salts in various forms are used in Nigeria as food seasoning and food additives. Potash is commonly consumed in Nigeria especially in the northern parts where two forms are commonly available: kanwa and shem. Kanwa, also known as natron, a sesquicarbonate or hydrated carbonate of sodium (Alawa et al., 2012). Kanwa is also known scientifically as trona (Omajali et al., 2010). Okehie-Offoha in 1996 however described kanwa as a potassium salt in combination with other salts. Kanwa is a base with a pH of 8.9. It contains 10% sodium as bicarbonates, 70% potassium, 0.33% calcium and 8% phosphorous (Yakasai et al., 2004).

[…]

Kanwa is used to soften food and reduce cooking time when boiling beans and tough meat. Kanwa is also an essential ingredient in making special porridges such as kunun kanwa literally translated from the Hausa language as 'saltpetre porridge' (Okehie-Offoha, 1996).

I'm just going to note this last bit is very similar to the sentence following the quotation from the Wikipedia article given in the question, which states:

It is also used to soften food and reduce cooking time when boiling beans and tough meat. Saltpetre is also an essential ingredient in making special porridges, such as kunun kanwa literally translated from the Hausa language as "saltpetre porridge".

Both of these cite the same source. I'd like to believe Sariem et al. actually went and found this source and verified what it said. But it unfortunately looks like they may have simply plagiarized a couple sentences from Wikipedia here, as this passage has been on Wikipedia since 2012, and their article didn't appear until 4 years later.

(Again, a warning about the dangers of Wikipedia. Even scholars overuse it without checking.)

Yet, as we know from the USAID report above, "kanwa" is apparently sometimes known as "saltpeter," even though as discussed in the Sariem et al. quotation above, we also know it's more correctly a form of potash, i.e., a potassium bicarbonate salt, along with sodium bicarbonate and some other minor components. ("Sesquicarbonate" and "hydrated carbonated" are synonyms for "bicarbonate.")

Sariem et al. is useful for summarizing a bit of the literature on the composition of kanwa. One final source I'll bring into the mix points out the regional variability of these salts:

Ngoualem et al., “Variability and Functionalities of Salts Used in Traditional African Food Preparations“ (2019)

Common edible salt, a natural evaporite which can be obtained from sea, underground ore or natural brine, and containing at least 97% of sodium chloride (NaCl), is the main salt used in food preparations, with the only objective to improve the taste of foods. Out of that, other specific salts which have been reported to be used in food preparations are Lakes’ deposits, plant-based ashes, their filtrates and evaporites of these filtrates. Their chemical composition shows that they are mixture of salts and thus, made of cations and anions, major cation being generally sodium or potassium whereas major anions are generally carbonates, bicarbonates, sulfates and chlorides. Their usages have mostly been reported in African countries (Nigeria, Niger, Chad, Cameroon, Ghana, Kenya, Burkina Faso, Uganda, Tanzania, Sudan, Central and East African countries) […].

In Africa, they have been reported to be used to reduce the cooking time of legumes, vegetables and cereals, to improve the green color of vegetables as well as to increase the viscosity of sticky ones, as emulsifier, and as flavor enhancers. These functionalities have been attributed to the alkalinity of their aqueous solutions. Since the solutions of Traditional Salts are alkaline, they can also be named Traditional Alkaline Salts (TAS).

To summarize the important bits from this last quotation:

• We might have various mixtures in these salts of sodium and potassium compounds, namely carbonates, bicarbonates, sulfates, and chlorides. Note, however, the conspicuous absence of nitrates. There's no potassium nitrate here.
• These salts are found in Ghana (as well as many other places).
• They are used to have the effects both listed in Wikipedia (incorrectly attributed to saltpeter/potassium nitrate) and in the recipe. They reduce cooking time of legumes, and they increase the viscosity of sticky ones (hence, I suppose, the "slime").
• The main aspect that makes these salts useful in cooking is their alkalinity in solution.

Hence, I finally arrive again at my initial recommendation: you need an alkaline solution. The most common item found in kitchens that will give you an approximation for this recipe is sodium bicarbonate, i.e., baking soda.

Lastly, I will note that the composition of these salts appears to vary significantly by region in Africa, but potassium (bi)carbonate seems to often be the most prominent ingredient, hence the alternative English name of "potash" for these salts. If you wanted a more authentic option, you could do an internet search for "kanwa" and find all sorts of interesting crystals people are selling. Or (if you're less adventurous) you could perhaps buy some pure potassium bicarbonate, then mix in a smaller proportion of baking soda, and you'll be most of the way there to something similar to the traditional West African culinary salts.

That said, I don't really think the important part here is the flavor from the salt, other than maybe some trace minerals (which likely vary significantly by source/region). Thus, baking soda will probably do in a pinch, and hopefully give you some nice slimy okra.

Answer 2

You seem to have two issues here.

The first is the lack of an exact measurement for the ‘saltpetre’. This is actually common for ingredients that are supposed to modify the texture of the final dish when looking at old recipes, because the goal is a specific consistency and historically the ingredients would have varied significantly in composition, so you would need to add the ingredient slowly, a bit at a time, until you got the right texture/consistency. If it’s your first time making this recipe and you have never had it before yourself, the best you can do is look up descriptions online and try to get as close as possible to what they describe, and then in future attempts adjust based on personal taste.

The second seems to be a mistranslation, compounded by misinformation on Wikipedia (the answer from Athanasius covers this with an excellent degree of research and explanation, so I won’t repeat it here).

Nitrate/nitrite salts are actually used in cooking, but they’re preservatives used for salt-curing meat (the classic pinkish-brown of a number of processed meat products, such as American hot-dogs, Bologna sausage, or some kinds of salami, is a result of these salts reacting with the myoglobin in the meat), and even that usage is falling out of favor due to related health risks. They definitely don’t react with okra or other vegetables in the way the recipe seems to describe.

What you actually need to achieve the described effect is to ensure the pH never gets too low. Okra seed pods work as a thickener because they contain a soluble form of fiber in the ‘slime’ inside the pods. Acids, even mild ones, will break this down rather effectively, and the most common method of ‘desliming’ okra seed pods is to cook them with acidic foods like tomatoes. By raising the pH, the ‘slime’ will thicken, which seems to be what the recipe is talking about. Thus, your best option here is probably either sodium bicarbonate (baking soda), or possibly potassium bicarbonate (sometimes called potash, though not always easily available as a food-grade ingredient).