The use of spices in cooking was long associated with aristocratic or wealthy settings, acquired through trade with small-scale producers (often hunter-gatherers even, at the initial point of collection) in southeast Asia. From the mid-19th to early 20th century, industrialization in the UK and America, and to some extent in Germany, the Netherlands, and France, produced a middle class of workers able to afford luxury items previously associated with wealth and opulence. Spices, along with dates, pearls, and tropical fruits, came into high demand. This process developed in parallel with the period of imperialism, where spice-producing regions around the Indian Ocean rim were fully brought into the British, Dutch, French, and American imperial systems.

A good case study is Zanzibar. Cloves were not grown on the island until they were introduced by way of Mauritius by a French planter around 1811. The Sultan of Muscat, Seyyid Said, who ruled Zanzibar and much of the East African coast, moved his capital to Zanzibar around 1830 and recognized the potential of cloves as a cash crop. He and other Omani landlords invested wealth gained through caravan trading (for slaves and ivory) and bought up much of the land on the island to intensively farm cloves, using mainland East African slaves as labor. Cloves were extremely valuable due to the high demand from American, Indian, and European consumers, who paid largely in cloth, which could be traded in the mainland for slaves and ivory. Some of the most favored cloth in mainland East Africa was called merekani, which was American cloth that was produced largely in textile mills in Massachusetts.

While caravan trading was one way to raise money to buy land, clove trees, and slaves, many planters also borrowed money from Indian creditors. Novel interpretations of Islamic property law allowed a planter to sell a piece of land to a creditor for a fixed price, and then be guaranteed to be able to buy it back after a certain amount of years at the same price. However, while the creditor had possession over it, the creditor was entitled to the products of the land, which were collected as interest. In this way, creditors could lend wealth and collect interest while technically skirting the Islamic prohibition against usury. These novel legal interpretations within Islamic law permitted transactions that supplied the lines of credit necessary for establishing and expanding large commercial clove plantations. When the clove market began to crash in the early 20th century (as clove production intensified in Madagascar and synthetic clove oil was also developed), many Omani and Zanzibari planters became hopelessly indebted to Indian creditors. It was only because British imperial policies favored Arabs as the landowning class that Omani landowners were permitted to keep their lands but remain deeply in debt. These tensions over land ownership contributed greatly to the Zanzibar Revolution in 1964 and the anti-Arab racial violence that followed.

In this way, Seyyid Said and other Omani landowners transformed a traditional East African merchant activity (slave and ivory trading) into that could produce a commodity for global consumer markets, and that was financed and funded through international systems of credit. For the first time, agricultural products, land and trees were quantified and commodified, and speculated on in financial markets. Unlike previous forms of subsistence agriculture in Zanzibar, clove farming was intensive and focused on production for export. While slaves had long been used for agricultural labor on the East African coast, it was only in the 19th (or possibly late 18th) century that slave labor took on many of the characteristic of American slavery, in the sense that slaves were worked and valued primarily for the monetary value of the crop they produced, and not just as a signifier of status.

Of course, this was also based on another commodity that was circulating in the Indian Ocean at the time-- industrial products. Clocks, guns, industrially produced ceramics, scientific instruments, eventually phones, trains, and cars, and other modern accoutrements were in high demand by the Zanzibari and Omani elite. The intensification of clove farming was as much a result of Omani and Zanzibari demand for industrial products as it was the result of middle class American and European demand for spices.

An interesting thing about this period is that while British abolitionists were working within the borders of the empire to eradicate slavery from about the 1870s onwards, slavery actually intensified from 1870-1920 or so due to the increased demand for the production of luxury products like spices in Zanzibar, and pearls and dates in the Persian/Arabian gulf. The British would use anti-slavery ideas as a justification to invade and occupy these regions and make them protectorates, but their actual policy on the ground was mostly to keep a hands-off approach to enforcing anti-slavery laws, because they were under enormous economic pressure to keep the spices flowing. Enforcing anti-slavery laws would have meant ousting local rulers and possibly causing disruptive insurrections which would have severely interfered with the trade in luxuries like spices. This is the argument that Matthew Hopper makes in Slaves of One Master: Globalization and Slavery in Arabia in the Age of Empire (2015), anyways.

another good book is A Sea of Debt: Law and Economic Life in the Western Indian Ocean, 1780-1950 by Fahad Bishara, 2017.

source: am phd student in this stuff