First off, what you read is correct. Liquors were an important trade item in the slave trade, although not the only or even the primary good traded. Quoting Tony Hopkins in _Economic History of West Africa_^1:

The leading import was cloth, which was in steady demand in an underdeveloped economy. Textiles of all kinds accounted fro between half and three quarters of the goods sent to West Africa from Rouen and Le Havre in the eighteenth century, and it is likely that shipments from other leading European ports were the same order of magnitude. In the seventeenth and eighteenth centuries cotton goods from Bengal were particularly prominent and it is interesting to reflect that on the eve of the industrial revolution that Europe still conducted a sizeable re-export trade in Indian manufactures.....Guns and Gunpowder were probably next in importance after cloth, and represented about one fifth of the value of cargoes shipped form England to Africa in the eighteenth century.....Hardware, principally utensils and tools, was probably third on the list of leading imports. Other well-known trade goods were salt, beads, bar iron, gin and brandy, all of which came from Europe, and tobacco and rum, which were shipped from the Americas.

Now, to the meat of your question. It is a slightly tricky question to say precisely when the Atlantic slave trade ends. The US banned the import of slaves from overseas in 1800, and Britain banned trans-atlantic slave trade in 1807. Britain put much diplomatic pressure on other European powers to end their participation in the Atlantic slave trade from the 1810s on, and Britain and the United States furnished navy ships for anti-slaving squadrons from the 1830s onwards. Despite this, there was still an illicit trade in slaves from West African ports to Brazil in the 1840s.^2 Robin Law has also observed that the period of "legitimate commerce" starting in the 1830s saw a commercial reorganization where networks of predation continued, but captives were mostly re-directed towards agricultural work producing ground nuts, palm nut oil, rubber, and other plantation goods in the hinterland near West African ports. So, a great deal of West African exports from the 1830s-1870s is produced through unfree labor. Which further blurs the lines of when "the slave trade" ends.

However, any way you slice it, yes, there continued to be a liquor trade between Europe and Africa through the nineteenth century and into the twentieth century.

In West Africa, there were initially continuities in the nature of liquor imports. In 1845 Ferdinand Gardner, the US consul to the Portuguese port of Bissau wrote^3:

Vessels of all nations are admitted to the Ports of Bissau and Cacheu, Africa, and Iron or Copper Nails for Shinglses, or Sheathing Vessels, Powder, Muskets, Cutlasses, Salt, French Wines & Liquors, Blue Baff, and All Kinds of Ardent Spirits not distilled from Wine, are admitted by paying the stipulated Duties.

Roughly contemporary to Gardner's account, we also have accounts of African traders who acted as middle-men and made great fortunes trading firearms, textiles, tobacco, cowries and liquors inland. A noted example of this type ofmerchant middle-man was an Egba woman, Efunatsan Anuwura. Based out of Ibadan in Yorubaland, she traded slaves, textiles, ivory and palm oil to Brazilian and Portuguese traders at Lagos and Porto Novo in the 1840s. Among the goods she received were tobacco, beads, textiles, liquor, guns and gunpowder.^4 She did this quite successfully and created an extensive commercial enterprise until her death in the 1874.

Similarly, in the Gold Coast, William Narh Ocansey acted as a palm oil exporter and accepted textiles, liquor and tobacco in the 1870s, trading with firms from London, Liverpool, Glasgow and Hamburg.^5 By 1877, Ocansey had a reputation as the most substantial trader in the Volta river region.

Turning again to Tony Hopkins for a broad overview of West African trade in the 1840s-70s^6 :

Four items accounted for about three-quarters of the value of all imports into West Africa. These were textiles (a classification covering a wide variety of cotten and woolen gods), spirits (especially rum and gin), salt and iron. Other prominent items were hardware, tobacco, guns and gunpwoder. Textiles remained the leading commodity, as in the eighteenth century.....Similarities between the types of goods imported before and after the end of the external slave trade should not be allowed to disguise some important differences:by the middle of the nineteenth century the quantity had increased greatly, and...the price per unit had declined.

On the European side of the trade, Britain and France continued to be the most important foreign powers on the West Coast, as they had been in the eigteenth century...In 1868 a French consul estimated that Britain and France shared four-fifths of Europes trade with West Africa, and two-thirds to three-quarters of this total was in the hands of Great Britain.....A new feature in the second half of the century was the rapid growth of German commerce. By the 1880s Hamburg was said to handle nearly one third of all West Africa's overseas trade. This expansion was the result of three factors: the rise of the palm kernel market, which was dominated by Hamburg because German farmers were the main buyers of the cattle cake, and becaus the Dutch were the largest manufacturers of margarine; the ability of Hamburg to supply cheap liquor; and the development of steamship services between Germany and West Africa.

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If we turn our attention away from West Africa, we still see the trade in liquor and wine playing an important role in Central and East Africa.

Let's take the example of Portugal. In the 1820s, after the independence of Brazil, the government in Lisbon was forced to contend with the reality of being a small country with a weak economy. Part of the response was to cut tariffs in the 1820s and encourage the export of Portuguese wine to Angola. Euro-African traders in Angola responded by planting sugar (using the labor of enslaved Africans from the interior) and distilling aguardiente, a sugar-cane based moonshine. This local production of aguardiente cut into wine imports.^7 A little bit later, in the economic slump of 1870s Portuguese metropolitan textile and wine lobbies became pressure groups encouraging imperial expansion in Africa.^8 This followed a common logic of European businesses which saw the expansion of European trade and empire as the expansion of markets and a solution to the economic depression of the 1870s.

In this era, liquors also played a role in European explorers' efforts to explore Central Africa. Explorers caravans included stocks of medicine like laudanum for treatment of tropical diseases like dysentery. They also included small stocks of liquors and brandies as items for the customary gift-exchange when making first contact with village heads and local potentates. Imbibing liquor or else pombe (palm wine) was an important element in facilitating audiences,^9 and played into central African understandings of power and alliance as cemented through the distribution of drink.^10 ^11

The colonial carve-up of Africa did result in some substantial changes in trade exchange between Europe and Africa. After European armies conquered African polities in the 1880s and 1890s, European powers drastically cut down in the trade of firearms and ammunition, keen to maintain a monopoly on violence.

European colonial powers also expressed concerns about the moral hazard of the liquor trade. European justifications for imperial rule in Africa commonly mentioned the moral imperative to end slavery on the continent, as well as the mandate to "uplift" Africans through Christianity and economic modernization. Liquor was thus seen as a "demoralizing" force that frustrate these efforts at uplift. You can see these attitudes in the 1890 Brussels Confrernce Act, an international agreement meant to ban the slave trade in tropical Africa, which included sections banning the trade in firearms and liquor.

However, Portuguese Angola was very lax in adherence to the protocols of the Brussels Act. Firearms and aguardiente continued to flow into neighboring Congo Free State and Northern Rhodesia through the 1890s and early 1900s^9 ^10, before the Portuguese took measures to crack down on aguardiente production in the early 1900s.

In 1919, the Convention of St Germain further tried to curb the importation of liquors into Africa. However, the British blockade on Hamburg from 1914-18 had already disrupted the export of liquors from that port to Africa.^14 Further tariffs on imports and trade limitations severely reduced the volume of liquors imported into African colonies in the 1920s.

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Sources

1 Economic History of West Africa by A.G. Hopkins. pp 110-111.

2 Wives of the Leopard by Edna G. Bay. pp 170-171. Talking about Felix de Souza's participation in slave trading in Dahomey in 1850s.

3 Brokers of Change edited by Toby Green. pp 317-318

4 Africa's Development in Historical Perspective edited by Akyeampong, Bates, Nunn, Robinson. pp 214

5 ibid pp 245

6 An Economic History of West Africa pp 129-130.

7 History of Central Africa vol 1 edited by Birmingham and Martin. pp 153, 159.

8 History of Central Africa vol 2 edited by Birmingham and Martin. pp 164

9 Out of Our Minds; Reason and Madness in the Exploration of Central Africa by Johannes Fabian. pp 68-70, 250-252.

10 The Drunken King, or, the Origin of the State by Luc de Heusch. pp 177-180

11 A Green Place, A Good Place by David Schoenbrun. Heinemann, 1998. pp 184-185.

12 History of Central Africa vol 2 pp 166-167

13 Objects of Life in Central Africa edited by Ross, Hinfelaar, Pesa. pp 260, 269, 279.

14 Economic History of West Africa pp 177-178