“Coffee should be black as hell, strong as death and sweet as love” is usually said to be a Turkish proverb, but no Turkish source has been cited. “Coffee, to be good, must be black as night, bitter as death, and hot as hell” was cited in an 1884 book about Brazil, but the speaker said it was a Turkish proverb. In 1889, the German recipe for coffee was said to be made “hot as Hades, black as night, strong as death, and sweet as love.”
 
Most 1800s and early 1900s versions of the coffee saying attribute it as a Brazilian proverb, but Brazil is not credited in any current literature.
 
 
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10 May 1862, Once a Week, ‘Dinners,” pg. 543, col. 2:
After you have done your drinking, let there be brought in,—in very small china cups,—coffee, which must be positively an essence, black as ink, strong as Hercules, and hot as—any simile you please.
 
Google Books
Round about Rio
By Frank De Yeaux Carpenter
Chicago, IL: Jansen, McClurg
1884, [©1883]
Pg. 48:
“The Brazilians are not intemperate in the use of alcoholic drinks, but they make this beverage immoderately strong.”
 
“They must have put the Turkish proverb in practice here,” said Robinson.
 
“And what is that?” asked Stacy.
 
“Coffee, to be good, must be black as night, bitter as death, and hot as hell.”
 
16 March 1886, Daily Republican (Mitchell, SD), “In Rio de Janeiro,” pg. 4, col. 2:
This is owing to the amount of strong black coffee they drink. A Brazilian proverb says that coffee to be good must be “black as night, as bitter as death, and hot as sheol.”
(...)
—Rio Janeiro Cor. New York Tribune.
   
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9 March 1889, The Deseret Weekly (Salt lake City, UT), “Letter from Egypt,” pg. 343, col. 3:
That is what they call coffee! The German gentleman must have thought of Oriental coffee when he said: “Coffee must be black as night, sweet as love, and hot as hell.” For that answers the description of Oriental coffee exactly.
   
PapersPast
14 December 1889, Evening Post (Wellington, New Zealand), Supplement, pg. 1, col. 8:
The Grand Duchess of Baden, whose table is said to be the best in all Germany, requires a good cup of coffee as the highest of all gastronomic luxuries, and a good cup of coffee, according to a German recipe, should be “hot as Hades, black as night, strong as death, and sweet as love.”
 
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The World and its People, Book 4
By Fanny E. Coe
Edited by Larkin Dunton
New York, NY:Silver, Burdett & Co.
1891
Pg. 246:
There is a Brazilian proverb that coffee, to be good, should be “black as night, and strong as death.”
 
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Dinners in Miniature
By Ethel Earl
London: Chapman & Hall
1892
Pg. 96:
As to coffee, there is the old French adage to go by: it must be “strong as death, black as night, sweet as love,” to which one might add, “and clear as truth.”
 
28 February 1892, Sunday Herald (Boston, MA), “Glimpses of Life in Algiers,” pg. 24, col. 2:
The coffee served by these Arabs is ever so much like that you get anywhere in London. “As black as night, as hot as hell and as sweet as love”—such is the beverage that every Oriental likes and must have.
   
Google Books
10 December 1892, Medical Review (St. Louis, MO), pg. 479, col. 1:
The Coffee Jag—Fannie B. Ward writes as follows from Rio Janeiro: (...) It is a common saying among Brazilians that coffee to be good must be as “black as night, bitter as death and hot as hades,” and at all hours of the day and night, in season and out, everybody literally guzzles it — made according to the proverb.
 
Google News Archive
2 September 1893, Ottawa (IL) Free Trader, “Coffee at the Fair,” pg. 7, col. 3:
It doesn’t meet the old Arabian test for coffee:— “as black as night, as strong as death, and as sweet as woman,” but it is very good, indeed, whatever its faults.
 
24 May 1896, Cleveland (OH) Plain Dealer, “Bab’s Letter” (from New York), pg. 5, col. 4:
But when one can breathe good air, what difference does it make about the coffee? Whether it is after the German fashion, black as night, sweet as love and strong as the devil, or whether it is from Sevres or the other thing?
 
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South America, Social, Industrial, and Political;
A twenty-five-thousand-mile journey in search of information in the isthmus of Panama and the lands of the equator, Colombia, Ecuador, Peru, Boliva, Chile, Tierra del Fuego, the Falklands, Argentina, Paraguay, Uruguay, Brazil, the Guianas, Venezuela, and the Orinoco Basin; the resources and possibilities of the various countries, the life and customs of the people, their governments, business methods, and trade
By Frank G. Carpenter
New York, NY: W.W. Wilson, publisher
1900
Pg. 519:
According to a naughty Brazilian proverb, good coffee should be “as strong as the devil, as black as ink, as hot as hell, and as sweet as love.”
 
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Brazil and Her People of To-day;
An account of the customs, characteristics, amusements, history and advancement of the Brazilians, and the development and resources of their country
By Nevin O. Winter
Boston, MA: L.C. Page and Co.
1910
Pg. 63:
In fact they drink so much that it must have got into their complexions. A Brazilian proverb says that good coffee must be as “strong as Satan, as black as ink, as hot as hades and as sweet as love.”
 
Google Books
February 1915, American Cookery, pg. 539:
Over the Coffee Cup
By Elsie Spicer Eels
“COFFEE,” says a Brazilian proverb, “should be black as night, as strong as the devil, as hot as Hades, and as sweet as love.”
 
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Living My Life (Vol. 1
By Emma Goldman (1869-1940)
New York, NY: Dover
1970
Pg. 490:
There he could read and rest to his heart’s content, or drink coffee “black as the night, strong as the revolutionary ideal, sweet as love.”
 
Google Books
Food and Drink:
A Book of Quotations
Edited by Susan L. Rattiner
Toronto, ON: Dover Publications, Inc.
2002
Pg. 9:
Coffee should be black as hell, strong as death, sweet as love. TURKISH PROVERB
   
Sydney (Australia) Morning Herald
Karnataka’s cuppa
June 10, 2012
Ben Stubbs gets a taste of life in a region that takes its coffee seriously.
“Coffee should be black as hell, strong as death and sweet as love.” This is the quote that greets visitors to the Indian Coffee Museum and it is a sentiment felt all through India’s coffee-growing south. I am in the small city of Chikmagalur in the Indian state of Karnataka.