Frankly, I'm confused. On the one hand, I'm surprised by how many mentions of it I've found in newspapers. On the other, given how regularly and widely it was imported, it's odd how little reference there is to it actually being consumed. Mostly it's just announcements of it arriving in port.
Several northern ports received shipments of Dantzig Black Beer. There was Hull:
HULL, DECEMBER 22.
For HAMBURG, The FAME, ALEXANDER GRANT, Master (A constant Trader.) To sail with convoy the 24th inst.
BLAYDES, LOFT, GEE, & Co.
A quantity of Podolia FLAX-
26 Casks of RAPE OIL
HORSE HIDES (dryed)
Ermland YARN from 12 a 25
Dantzig BLACK BEER (One property.)
22d Dec. 1800.
Hull Packet - Tuesday 23 December 1800, page 3.
For SALE, REAL SPRUCE BEER, just arrived from Dantzic direct.
TOMLINSON & BOOTH.
HULL, October Ist, 1814.
Hull Packet - Tuesday 04 October 1814, page 2.
VIN DE BOURGOUGNE.
Very superior BURGUNDY WINE, in Bottles, Selected with great care, and bottled in France for Private Tables. A few Cases only being left, will be disposed Of on reasonable terms.
Also, Dantzig BLACK BEER, in Kegs and Half-kegs.
Apply to B. H. DOWNING, 40, Chapel-walks, POOl-lane.
Liverpool Mercury - Friday 15 December 1826, page 4.
DANTZIG BLACK BEER.
ON SALE, Part of a Cargo, recently landed from the Elise, 10s. 6d. per Keg,
BY GEO. FINLAY,
WINE MERCHANT, BIGG-MARKET.
Newcastle. 9th Jan. 1846.
Newcastle Journal - Saturday 10 January 1846, page 2.
ALLSOPP'SPALE AND BURTON ALES.
The above ales are now being supplied in the finest condition in bottles and casks.
Also, just landed, PRIME DANTZIG BLACK BEER, in kegs.
By GILPIN AND COMPANY, 107, Pilgrim-street, and 7, Manors.
Newcastle Guardian and Tyne Mercury - Saturday 02 February 1867, page 1.
Note the mention in several of the above of "kegs". The term was usually used to refer to small barrels rather than the type of barrel in which beer was delivered.This confirms the small size of the barrels used to export Dantzig Black Beer:
"Danzig. The demand for Jopenbier was very limited, as in the English manufacturing districts, the main sales locations for this article, most workers were unemployed because of the American war. The sale price was 70 fr. per 1/4 T. free on board. Manufactured were 22300, exported 24300 1/4-T. Value of 56700 Th; of the shipped amount a great part was sent to England on credit and stored there unsold. The stock at year-end was 8000 1/4-T."1/4 T I assume means a quarter Prussian tonne. That had a capacity of 114.503 litres, or a little over 25 gallons, making a quarter tonne about 6.25 gallons, or
"Preussische Statistik" 1863, page 101.
And finally . . . a medicinal use for Black Beer:
Infallible Cure for Colds.—Two tablespoonfuls of Dantzig black beer, taken with hot water, sugar, and about half-a glass of old rum, or malt whiskey, immediately before going to bed, is said to cure the most obstinate and long-standing colds, and has succeeded where every other remedy failed.
Bucks Herald - Saturday 07 January 1843, page 7.
There may be more, depending on how my searches with variations in the spelling work out.
* Brewers' Almanack 1928, p. 115