Gum arabic

• 1. Introduction

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  Gum arabic sits inside an M&M's candy, on the back of a postage stamp and in a tin of shoe polish. It is the hardened sap of acacia trees that grow across the Sahel, the dry belt south of the Sahara. Few of the people who handle it every week have any reason to learn its name.

  The questions begin with that name. Why does a product of African trees carry the word Arabic? Why did European powers fight over a lump of dried gum? And what happens to the factories that depend on it when the places that supply it are thrown into turmoil?

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• 2. A Name Without a Tree

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  By the 9th century, people in the Middle East were already calling this substance gum Arabic. When it later reached Europe through Arabic ports, it kept the name of the place that sent it. Other labels exist too, including gum acacia, gum sudani and Senegal gum.

  From the 19th to the 23rd of March 1999, the 31st Codex Committee for Food Additives met at The Hague and settled on a formal definition. Gum arabic, it ruled, is the dried exudate from the trunks and branches of Acacia senegal or Vachellia seyal, both in the family Fabaceae, also called Leguminosae. Under the broad meaning of Acacia used before 2005, those two species are now named Senegalia senegal and Vachellia seyal.

  A 2017 safety re-evaluation by the Panel on Food Additives and Nutrient Sources of the European Food Safety Authority added a warning. The panel said the definition holds for most internationally traded samples. But the words gum arabic do not point to one botanical source. In a few cases, material sold under that name did not come from Acacia at all, and was instead gathered from Combretum or Albizia.

  Those cases are the exception. The genuine product is harvested commercially from wild trees, in a belt that runs from Senegal to Somalia.

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• 3. Harvest in the Sahel

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  A band of acacia country once ran across much of the Sahel, from the Atlantic Ocean to the Red Sea. Harvesters tap these trees by stripping small pieces of bark away. The wound is what makes the tree exude its gum.

  Traditionally, the work belongs to seminomadic desert pastoralists. They collect the gum as they move through their transhumance cycle, the seasonal journey of herds between pastures.

  Today the main gum-producing populations of Acacia stand in fourteen countries. They are Mauritania, Senegal, Mali, Burkina Faso, Niger, Nigeria, Chad, Cameroon, Sudan, Eritrea, Somalia, Ethiopia, Kenya and Tanzania. Gum arabic remains a main export of several of them, including Mauritania, Niger, Chad and Sudan.

  In 2019, total world exports were estimated at 160,000 tonnes. That figure had recovered from two earlier crises, one in 1987-89 and another in 2003-05. In both, the desert locust destroyed trees.

  Gum had been harvested in Arabia and West Asia since antiquity. Yet the gum from south of the Sahara was already a prized export long before locusts disturbed the market.

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• 4. The Gum Wars

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  In 1445, Prince Henry the Navigator set up a trading post on Arguin Island, off the coast of modern Mauritania. The post acquired acacia gum for Portugal, and it also acquired slaves. When the Portuguese and Spanish crowns merged in 1580, the Spaniards became the dominant influence along that coast.

  In 1638, the Dutch replaced the Spaniards and became the first to exploit the gum trade seriously. Their gum came from the acacias of Trarza and Brakna, and it was considered better than the gum previously obtained in Arabia. By 1678, the French had driven out the Dutch. They built a permanent settlement at Saint Louis, at the mouth of the Senegal River.

  Textile printing explains the appetite. Gum arabic became essential to cloth printing, and so to the pre-industrial economies of France, Great Britain and other European countries. Their rivalry over the commodity was so fierce throughout the 18th century that some historians call it the gum wars.

  By the 18th century, West Africa was the only source of the world's acacia gum. For much of the 18th and 19th centuries, it was the major export of the French and British trading colonies in modern Senegal and Mauritania. At Saint-Louis, exports doubled in the 1830s alone.

  Then the Emirate of Trarza threatened to send its gum to British traders at Portendick. That would have bypassed Saint-Louis and its taxes, and it pushed Trarza into direct conflict with the French. The new emir, Muhammad al Habib, had already struck a deal with the Waalo Kingdom, directly south of the river. He agreed to end raids on Waalo territory, and in return he took the heiress of Waalo as his bride.

  French traders saw danger in that marriage. Trarza might inherit control of both banks of the Senegal. In the Franco-Trarzan War of 1825, the French sent a large expeditionary force that crushed Muhammad's army. The war drew the French north of the Senegal River for the first time, and it marked the start of their direct involvement in the interior of West Africa.

  Gum kept flowing in large quantities from French West Africa, from French Equatorial Africa and from British-administered Sudan. That lasted until these nations gained independence in 1959-61, and one of them would soon dominate the trade.

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• 5. Sudan's Grip

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  Since the 1950s, one country has dominated the world's supply of gum arabic, and that country is Sudan. In the early 2020s, about 70 percent of the global supply came from there. Roughly 5 million Sudanese people, more than 10 percent of the population, depend on the gum for their livelihoods, directly or indirectly.

  Market reforms arrived in 2019. After them, official figures put Sudan's exports at about 60,000 tonnes in 2022. Exact numbers are hard to pin down, because some of the production happens in regions that are difficult to reach.

  Before those reforms, the Sudanese government heavily dominated production. In some periods it tried to use the gum's importance to the world market as pressure against other countries.

  The 2023 Sudan conflict interrupted exports. Because the gum could no longer be shipped out, its price inside Sudan crashed. Meanwhile, international companies that rely on it have started trying to diversify their supply chains, and some are searching for ingredients that could replace it.

  The idea of replacement is not new. In many uses, other substances have already taken its place.

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• 6. Food and Fiber

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  Gumdrops and marshmallows still depend on gum arabic, as does the syrup behind soft drinks. Elsewhere, other substances have replaced it wherever toxicity is not a worry. The reason is that the chemical proportions in the gum vary widely, which makes it unpredictable.

  In icing, fillings, soft candy and chewing gum, it works as a stabiliser, an emulsifying agent and a thickener. In soft drinks, it binds the sweeteners and flavorings. Bartenders sometimes use gomme syrup, a solution of sugar and gum arabic in water. It keeps the sugar in a cocktail from crystallising and gives the drink a smooth texture.

  A daily dose of 30 grams, about 1 ounce, or more can cause harmless flatulence in some people. Gum arabic is a soluble dietary fibre, and it is generally recognized as safe for human consumption. It passes through the stomach without being broken down. Microorganisms in the large intestine ferment it into short chain fatty acids. That makes it a prebiotic, which is different from a probiotic.

  How many calories it supplies has never been settled. An upper limit of 2 kcal/g was set for rats, but that figure is invalid for humans. The US FDA first set a value of 4 kcal/g for food labelling, while Europe assigned no value to soluble dietary fibre. A 1998 review concluded that "based on present scientific knowledge, only an arbitrary value can be used for regulatory purposes". In 2008, the FDA sent a letter of no objection in response to an application to reduce the rated value to 1.7 kcal/g.

  Laboratory and animal studies have reported a long list of possible benefits. They include better absorption of calcium, lower body mass index and body fat percentage, and lower total cholesterol, LDL and triglycerides. Other reported effects are antioxidant activity, kidney and liver support, immune modulation, and a stronger intestinal barrier. In rats, the gum protected the intestine against the drug meloxicam. Some of these benefits may be present, but they need further verification.

  It also slows the rate at which the gut absorbs some drugs, amoxicillin among them. Pharmaceutical drugs and cosmetics use it as a binder, an emulsifier and a suspending or viscosity-increasing agent. Even winemakers have used it, as a fining agent.

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• 7. Studio and Press

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  Every tube of watercolor depends on a simple partnership. Pigment of any color is suspended in gum arabic in varying amounts, and water acts as the vehicle that thins the paint and carries it onto paper. When the moisture evaporates, the gum typically does not hold the pigment on the surface. It is absorbed into deeper layers.

  Painters who use little water get a different result. The gum then acts as a true binder in the paint film, increasing luminosity and helping stop colors from lightening. It spreads pigment particles evenly, which gives subtler control over washes. It also slows the evaporation of water, so the painter works a little longer. A touch of extra gum makes it easier to lift pigment off the paper.

  Potters have added gum arabic to ceramic glazes for a long time. Before firing, it helps the glaze stick to the clay and limits damage from handling. It also thins the glaze mixture, though the mixture is then more likely to settle into a hard cake if left unused. The gum is made into a hot water solution, typically 10-25 g/L. It goes into the glaze after any ball milling, at 0.02% to 3.0% of the glaze's dry weight. In the kiln it burns out at a low temperature and leaves no residue. Commercial manufacturers often swap it for more consistent alternatives such as carboxymethyl cellulose.

  Gum bichromate photography mixes gum arabic with ammonium or potassium dichromate and pigment. The result is a coloured emulsion that becomes relatively insoluble in water after exposure to ultraviolet light. Gum that has not reacted washes off in warm water. The gum that did react stays behind and permanently binds the pigment to the paper.

  In lithography, plain gum can etch very light tones, such as those drawn with a number-five crayon. Phosphoric, nitric or tannic acid is added in varying strengths to etch darker tones, all the way to dark blacks. The etch forms a gum layer that attracts water, so oil-based ink does not stick to those areas. The same treatment keeps the non-image areas of a plate receptive to water. It also stops aluminium plates from oxidising between processing and the press. Gum is essential to paper lithography too, which prints from an image made by a laser printer or photocopier.

  At home, the gum shapes incense cones, and it is the lickable adhesive on envelopes and cigarette papers. In fireworks, it serves as a water-soluble binder in the composition.

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• 8. Makeup and Meaning

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  Arabinogalactan, a polymer built from the sugars arabinose and galactose, is a major component of gum arabic and of many other plant gums. Chemists have identified a compound called 8-5' noncyclic diferulic acid, covalently linked to the carbohydrate parts of its arabinogalactan-protein fraction. Overall, the gum is a complex mixture of glycoproteins and polysaccharides.

  Long before anyone mapped those molecules, European poets gave the gum a meaning. Between the 13th and 17th centuries, writers including William Shakespeare and the Dutch poet Jacob Cats used gum arabic to represent the noble Orient.

  In the Sahel, where the trees grow, it stands for something else entirely. There the gum is a symbol of the purity of youth.

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