PDF Summary:Salt, by Mark Kurlansky

Salt is one of the cheapest, most commonplace items: It sells for less than a loaf of bread, and during winter, we scatter it liberally on roads and sidewalks. However, there was once a time when salt was considered rare and valuable. In Salt, Mark Kurlansky argues that throughout much of human history, salt was a precious commodity—one that significantly shaped civilizations.

In this guide, we’ll present Kurlansky’s history of salt, describing the role it played in nourishing our ancestors, driving innovation, building empires—and even provoking rebellions. You’ll learn why salting food isn’t just about improving its flavor, why salt harvesting causes sinkholes, and how salt played an important role in several independence movements. Throughout this guide, we’ll supplement Kurlansky’s history of salt with relevant concepts in chemistry, food science, and geology. We’ll also update the book’s ideas with recent research on how we harvest and use salt today.

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Where Is Salt Found?

Kurlansky explains that salt is found:

• In water: Salt is found in oceans, springs, and some lakes.
• Underground: Underground salt deposits containing rock salt (salt in hard, mineral form) can span hundreds of miles. Some take the form of salt domes (mounds of salt that form when tectonic activity forces underground deposits upward).
• Above ground: Some mountains also contain large deposits of rock salt.

According to Kurlansky, for centuries, scientists have wondered and debated why the earth is so rich in salt. Today, there’s a general consensus that salt deposits on land and underground got their salt from the ocean—but scientists don’t agree on why ocean water is salty.

The Origin of Earth’s Salty Oceans and Salt Deposits

Since the publishing of Salt in 2002, scientists have converged around a theory that there are two main processes that continually replenish the ocean’s salinity (saltiness):

Process 1: Hydrothermal vents increase the salinity of ocean water. First, low-salinity ocean water flows into these cracks in the seafloor until it reaches magma below the earth’s crust. Next, this magma heats up the water, causing chemical reactions that form minerals (including salt). Finally, hydrothermal vents and underwater volcanoes return this high-salinity water to the ocean.

Process 2: Land runoff flows into the ocean. Rainwater erodes rocks on land, creating a solution of dissolved salts that flows into nearby waterways (such as rivers). Eventually, these waterways flow into the ocean.

Geologists also explain how the ocean played a role in creating salt deposits above and below the ground, a topic that Kurlansky doesn’t explain in detail. Earlier in Earth’s history, shallow seas spanned entire continents. As the Earth cooled and its climate became drier, much of this seawater evaporated, exposing land masses. However, some of this water collected in land basins that were caught in a cycle of evaporating and then receiving an influx of new ocean water. Over time, this cycle left behind salt deposits. Tectonic activity then altered the depth of these deposits: Some were forced deeper underground, and others were pushed upwards (forming salt domes and salt-filled mountains).

Innovations in Harvesting Salt

Method 1: Solar Evaporation

According to Kurlansky, the oldest and most common method of harvesting salt is relying on the sun to evaporate water from lakes and the sea. This process leaves behind salt crystals. The ancient Chinese pioneered this method: As early as 6,000 BCE, they raked and collected salt crystals that formed on lake beds in the summer. Eventually, they and others around the world started making artificial ponds by collecting seawater and lakewater on land.

In the Middle Ages, the North African Muslims were likely the first to develop a more advanced, efficient method of solar evaporation. First, they collected seawater in an artificial pond and waited for it to partially evaporate. Next, they used pumps and gates to move this water into another pond (or a series of ponds) where it would evaporate further. Finally, new water was pumped into the first pool to start the evaporation process anew. This process was efficient because it allowed for simultaneous evaporation across multiple ponds.

Today, people continue to use various methods of solar evaporation to produce salt.

Solar Evaporation Methods Used Today

Some small-scale, artisan salt producers continue to use a method of salt-raking similar to that used by the ancient Chinese. For instance, salt harvesters in Hawai’i use traditional methods to evaporate seawater in shallow, man-made ponds. They rake white salt from the ponds and use it in two ways: They either use the salt to season food, or they mix it with red clay and use it for healing and ritual blessings.

Furthermore, both artisan and industrial salt producers continue to use multi-pond solar evaporation methods similar to those likely developed by medieval North African Muslims. Recent research demonstrates that halophilic bacteria (salt-loving bacteria) improve this multi-pond evaporation process. Salt ponds containing halophiles evaporate faster: These bacteria absorb light energy due to their red color, which raises the ponds’ temperature and hastens evaporation. Furthermore, these bacteria’s chemical reactions reduce the number of impurities (such as calcium and magnesium) among the salt crystals.

Method 2: Mining

Kurlansky claims that drilling is the main way to harvest underground brine. The Chinese lay claim to the first innovation in salt drilling: Around 250 BCE, they used bamboo tubes to siphon brine out of wells. Around a millennium later, they used percussion drilling to dig deeper. This process involves a seesaw-like lever that pounds a metal rod into the ground.

(Shortform note: Why were the ancient Chinese consistently the first to invent a wide variety of salt-harvesting methods? In Guns, Germs, and Steel, Jared Diamond claims that for most of ancient and medieval history, China was much more technologically advanced than other regions around the world—for instance, the Chinese were also the first to invent cast iron, gunpowder, magnetic compasses, and paper. According to Diamond, one likely factor behind China’s early inventiveness is that food production began relatively early in Asia due to geographic and environmental factors. This led to population booms, and inventions tend to arise and progress rapidly in areas with higher populations.)

In the Middle Ages, people developed a more efficient way of mining salt: solution mining. This method involves pumping water into mines, siphoning out brine, and boiling it. According to Kurlansky, modern salt producers today continue to engage in solution mining, and they evaporate the brine using machines called vacuum evaporators.

(Shortform note: Today, some salt producers continue to evaporate brine using vacuum evaporators—but instead of getting the brine from underground deposits like the medieval Austrians, they use brine produced by desalination plants. These plants convert seawater into freshwater for agriculture and drinking, and high-concentration brine is a byproduct of this process. These plants typically release this brine back into the ocean. Some experts argue that using this byproduct for salt production instead has two benefits. First, it speeds up the vacuum evaporation process, since the brine is already concentrated. Second, it’s more environmentally friendly than releasing the brine into the ocean, which studies reveal harms marine life.)

In modern times, salt drilling led to the expansion of new industries, such as the oil industry. In the early 20th century, harvesters drilling into a Texan salt dome unexpectedly hit oil, and soon, the US and other countries began extracting oil by drilling near salt.

(Shortform note: Kurlansky describes this discovery in Texas as one that transformed the oil industry generally, but this may be an overstatement. This event expanded the oil industry in the US specifically, but prior to this, major overseas oil companies had already expanded to global markets. For instance, by the late 1800s, the Russian oil industry was already exporting oil globally.)

Oil and natural gas often gather near salt because salt deposits form dense barriers around which organic material accumulates. Over time, this organic matter decomposes, becoming valuable fuel.

(Shortform note: While many salt domes provide a reliable source of oil, drilling for oil near salt can contaminate the oil with salt. Salt-contaminated oil corrodes metal machines in oil refineries, and it can be costly to repair these machines.)

Other Salt-Related Innovations

According to Kurlansky, salt has also played a key role in other technological innovations beyond those related to salt harvesting. Here are several examples:

• In ancient times, Egyptians used salt to preserve bodies for mummification. (Shortform note: Today, embalmers continue to include salt in their process, along with other compounds such as formaldehyde.)
• The ancient Chinese used saltpeter (potassium nitrate) to invent gunpowder. (Shortform note: Saltpeter is no longer used in gunpowder. However, it’s still used in various products such as pesticides, fertilizers, and fireworks.)
• In the Middle Ages, people used salt for various purposes, such as glazing pottery. (Shortform note: Industrial pottery production no longer relies on salt glazing, but some potters still use this method.)
• Today, people use salt to de-ice roads because salt lowers water’s freezing point. (Shortform note: Recently, several cities have instead started de-icing roads with sugar beet juice (which also lowers water’s freezing point). Some claim sugar beet juice is a more eco-friendly and cost-effective de-icer compared to salt.)

Salt Industries’ Impact on the Environment

Kurlansky argues that throughout history, salt industries and salt-related innovations have degraded the environment. Environmental damage in the English county of Cheshire, England’s leading salt producer for several centuries, exemplifies several of the ways salt industries can degrade the environment:

• Destruction of forests. Wood fueled Cheshire’s brine-boiling process of harvesting salt, and by the 17th century, salt harvesters had cleared most of the county’s forests.
• Air pollution. In the late 1800s, coal-burning furnaces fueled brine-boiling—and filled Cheshire’s skies with black plumes of soot.
• Sinkholes. Starting in the 18th century, sinkholes began wrecking homes and bridges in Cheshire. When harvesters pumped excessive brine from underground reserves, groundwater filled the gaps and dissolved the salt rock, causing sinkholes.

Salt Industries’ Impact on the Environment Today

Although today’s salt harvesters no longer rely on forest wood for fuel, modern industries that produce and rely on salt production continue to contribute to air pollution and the formation of sinkholes. For instance, one of the high-profile environmental disasters, the Bayou Corne Sinkhole Disaster, was a result of excessive salt drilling. In 2012, a Texas driller that produced brine for the chemical industry created a 37-acre sinkhole that caused small earthquakes, killed trees, and forced many local residents to relocate.

Since the 1970s, there’s been a growing interest in salt harvesting methods that rely on solar energy due to evidence that this method can prevent environmental degradation. For example, Indian salt harvesters have prevented over 12,000 metric tons of carbon dioxide from entering the atmosphere by pumping brine using solar energy instead of diesel generators. Furthermore, solar saltworks (salty habitats where you can harvest salt) can protect and rehabilitate land that other industries have degraded. For instance, solar saltworks increase biodiversity because they protect salt marshes, where many plants and animals thrive.

Salt’s Economic and Political Significance

Salt industries throughout history may have damaged the environment, but leaders of salt industries believed this damage was worth it—because salt production was extremely lucrative. Kurlansky argues that for most of human history, salt had both economic and political significance due to the profitability of the salt industry. In this section, we’ll explore how salt has shaped economies and politics for millennia. We’ve organized this section into three themes: the role salt played in 1) trade, 2) empire-building, and 3) rebellions and wars.

Theme 1: The Salt Trade Was Widespread

According to Kurlansky, salt was one of the first commodities traded over vast distances. For instance, around 2800 BCE, Egyptians exported salted fish to the Phoenicians, who occupied the North African coast. The Phonecians then traded Egyptian salted fish and North African salt with the rest of the Mediterranean.

(Shortform note: Other historical records reveal that the ancient Egyptians may have been engaged in long-distance trade of other goods even earlier than this. Artifacts from the fourth millennium BCE reveal that pre-dynastic Egyptians traded with ancient Mesopotamians. Gold may have been one of the commodities they traded. Furthermore, new archaeological evidence suggests that Phoenicians not only traded salt produced by others (such as Egyptians and North Africans) but also eventually formed colonies on the Atlantic coast of the Iberian Peninsula to produce their own products for export, including sea salt.)

Why was salt such a valuable, widely traded commodity? Kurlansky provides two reasons. First, salt was precious because, as we explored earlier, all humans and livestock need it to survive. (Shortform note: Humans and animals still need salt to survive today—so why is it no longer considered precious? One reason may be that salt is no longer scarce due to technological developments related to locating and harvesting salt. Only 6% of salt produced today is used for human consumption, suggesting that there’s ample salt to meet our dietary needs.)

Second, salt was widely traded and highly valued because not all regions had easy access to this mineral. Salt industries arose where it was easy to harvest salt, such as areas with plenty of coastlines (for sea salt production). These regions traded with areas that had less access to salt and therefore considered salt highly valuable, such as northern countries whose climates were too rainy or dark to efficiently evaporate water from sea salt.

How Access to Salt Influences Economies Today

Although salt is no longer as scarce a resource today as it was throughout ancient and medieval history, some regions around the world continue to have higher access to salt than others. Because of this, salt continues to be a valuable, widely-traded commodity. It’s not just northern countries that struggle to produce salt: Maps of global salt deposits reveal that some more southern inland areas, such as central Africa, lack access to both coastal sea salt and underground salt deposits. Regions lacking access to natural salt deposits depend on imports from other countries.

Additionally, some areas with access to salt (such as areas with plenty of coastlines) still depend on foreign imports of salt for other reasons. For instance, the Philippines no longer produces much salt and relies on foreign imports for more than 90% of its salt needs. One reason they depend on foreign imports is that salt farms along the Filipino coast have been demolished to make room for commercial ventures, homes, and other industries.

Furthermore, climate change is altering salt production and which regions have access to producing salt:

• In regions that rely on solar evaporation, increased rains are threatening salt production. For instance, heavy rains in Cambodia have led to a steep decline in their salt harvest. As a result, salt prices in Cambodia have surged.

• On the other hand, climate change is causing drought in other areas—drought that improves solar evaporation, boosting sea salt production. For example, sea salt production in France nearly doubled due to droughts that are linked to climate change.

Theme 2: Control Over Salt Strengthened Empires

Kurlansky argues that because salt was so profitable, many empires expanded their territories, grew rich, and increased their power by controlling salt industries. For instance, in ancient China, the Qin dynasty instituted a state-controlled monopoly over salt. Revenue from their salt monopoly funded armies and defensive structures such as the Great Wall of China.

(Shortform note: China’s state-controlled salt monopoly was not only a policy of the ancient past: This monopoly continued until only recently in history. In 2017, the Chinese government started allowing salt producers to determine their own prices and sell directly to the market).

Empires also strengthened their economic power by colonizing areas that were rich in salt. For example, in the 17th century, Britain harvested and profited off salt from its Caribbean colonies, such as Bermuda. It traded this salt with North Americans in exchange for salt cod. Enslavers fed this salt cod to enslaved Caribbeans working on sugar plantations.

(Shortform note: In Guns, Germs, and Steel, Jaren Diamond argues that Europe’s advanced technology, including salt harvesting technology, was a factor leading to their conquest of the Americas. According to Diamond, European societies were technologically advanced because they had geographic advantages such as a temperate climate. These advantages led to ample food production, causing population booms, the development of industries, and new inventions. Critics claim that this argument makes it seem inevitable for geographically-advantaged regions like Europe to colonize. These critics accuse Diamond of downplaying the role that Europeans’ colonial and racist ideas played in their decisions to conquer the Americas.)

Theme 3: Power Struggles Over Salt Fueled Rebellions and Wars

Kurlansky makes clear that throughout history, people in colonized regions often resisted empires’ control over salt industries. They staged rebellions (which often turned into wars) to demand that empires grant them autonomy over salt production and profits. Let’s explore two examples of this: the role conflict over salt played in the American Revolution, and the role it played in the Indian Independence Movement.

Example 1: The American Revolution

According to Kurlansky, the American-British conflict over salt was one of the catalysts for the American Revolutionary War. Let’s trace the events that led to this war.

First, in the late 1600s, the British noticed and grew worried about self-reliance among American colonists. Many of these colonists were producing their own salt, which threatened the British ideal of how a colonial relationship should work: one in which the colonists depended on Britain and sold all their commodities to Britain.

To discourage this self-reliance and trade, the British took two actions that increased American dependence on British salt. First, they made British salt cheaper than colony-produced salt so that colonists would buy British salt instead. Second, the British forbade colonists from trading salt with foreigners.

Kurlansky argues that Americans’ anger over British control of their salt production and trade was one of the factors that contributed to the tension between Britain and the American colonists—tension that eventually boiled over into war. In the mid-1700s, Britain sensed American colonists’ desires for independence, so they enacted taxes and tariffs to discourage American trade with foreigners, and they stationed troops in Boston to quell any American resistance. In 1775, enraged and armed American colonists fired on these troops, beginning the American Revolutionary War.

Other Catalysts for the American Revolutionary War

Kurlansky identifies the conflict over salt as one of the catalysts behind the American Revolutionary War, but he doesn’t mention the other catalysts that arguably played a more direct role in initiating the conflict. Historians argue that several British laws that taxed American colonists, as well as limited their trade and self-sufficiency, contributed to Americans’ desire for independence.

For instance, one of these laws, the American Revenue Act (also known as the Sugar Act), increased taxes on several goods to raise revenue for Britain. The law increased American colonists’ resistance to British rule because they believed that it was a violation of their rights to tax them without allowing their representation in Parliament. The Sugar Act was arguably a greater catalyst for the War than the salt taxes because the idea of “no taxation without representation” was a crucial issue and a rallying call behind American resistance to British rule.

Example 2: The Indian Independence Movement

According to Kurlansky, India’s independence movement also began as a conflict over salt production. The conflict started brewing in the 18th century when the British worried that the high-quality salt produced in India would threaten the profits of salt produced in England. To prevent this, they established a British monopoly over salt made by Indian saltworks, requiring Indian salt producers to sell all their salt to the British. Indian salt harvesters staged a rebellion against this monopoly in 1817 by attacking British-controlled saltworks in India.

Indian resistance to Britain’s control of salt production reached new heights in the early 1900s when Indians grew upset about the high tax Britain required them to pay on salt. The Indian Legislative Assembly demanded that Britain reduce this tax, but Britain refused. Mahatma Gandhi began organizing Indians to engage in nonviolent resistance against British control of India, and one of his best-known efforts was his 1930s salt campaign.

Gandhi’s salt campaign kicked off the Indian Independence Movement. He and his followers walked nearly 250 miles along the Indian coastline, gathering sea salt—which was illegal under British law. Within a week, the salt campaign became a national movement of over 100,000 Indians. British police responded to salt campaigners’ civil disobedience with arrests and brutal violence. But the campaign worked: In the early 1930s, the British signed a pact promising to release political prisoners and permit Indians to collect sea salt. According to Kurlansky, this pact and Gandhi's campaign paved the way for Indians to secure their independence in 1947.

Why Salt Played a Pivotal Role in the Indian Independence Movement

While Kurlansky emphasizes the important role salt played in the movement for Indian independence, he doesn’t clarify why salt in particular played such a pivotal role. According to experts on social movements, Gandhi selected salt for his campaign for nonviolent resistance for several reasons:

Reason 1: The salt campaign increased the involvement of lower-class Indians. Britain’s salt tax disproportionately affected lower-class Indians, who needed salt but couldn’t afford the tax. The majority of India was poor or lower class. By appealing to them, Gandhi’s movement gained a large following.

Reason 2: Salt united Indians from different backgrounds. Gandhi’s salt campaign enlisted the support of anyone who had access to seawater—and that group included Hindus and Muslims from various social castes. Choosing an issue (salt harvesting) that affected such a wide range of people ensured diverse groups would unite into a national movement.

Reason 3: Salt made Indian independence tangible. The idea of independence was abstract, so Gandhi chose salt—something you can hold—as a symbol of Indian labor, self-sufficiency, and independence. Today, salt continues to be a symbol of India’s hard work and self-sufficiency.