Primings (part one)

By the end of the 19th century, there were clear regional variations in Porter and Stout. While, in London, brewers stubbornly clung to the use of brown malt, those outside the capital opted or simpler grists, often just pale and black malt.

Without the same mass-market or Black Beers which existed in London, provincial brewers needed to turn them around quickly. And that meant using "heading" to bring them into condition quickly. This heading could either be in the form of flour or a sugar solution. The latter being what we would now call primings.

"Country black beers.
I now come to the country as a whole, for outside London and Dublin the production of black beer is carried on in no very distinct manner; some brewers softening water, some using sugar, others employing malt-flour, and sugar solutions for heading purposes, and most falling back upon some definite preservative agent to prevent early deterioration. As a rule, country brewers have no very heavy demand for their black beers, and they have to brew them accordingly— i.e., if for immediate sale, and if prompt draught can be relied upon, country brewers imitate, to a certain extent, the example set them by Londoners, using sugar as a portion of the extract, raw sugar solution as the heading.

On the other hand, the majority, bound to produce an article of some stability, and one that will only come into condition after considerable storage, strictly adhere to entire malt brewings with low initial temperatures of mash, comparatively brief standing periods, fermentations progressing with free range of heat, racking their beer sometimes as high as third of original gravity. Finally, they employ some definite kind of heading, either introducing it at the racking stage, or at period of shipment. Many different varieties of heading have found favour, some of them being substances easily fermentable, others practically wort in a state of fermentation, or when in the state of dry flour forming, as we may suppose, the food of ferments.

Quite recently it has been suggested that flour only acts in the sense of being the store-house of so much air; but this view seems hardly correct in face of the act that the addition of flour to black beer undoubtedly leads to secondary fermentation, more or less prolonged in character, and I think there is no doubt that the crude albuminous matters of raw or malted grain become slowly modified into yeast-forming material when placed in a fluid undergoing fermentation.
"The Theory and Practice of Modern Brewing" by Frank Faulkner, 1888, pages 268-269.

Faulkner also mention a couple of other methods. First, the old-fashioned method. Which was to rack the beer with plenty of remaining fermentable materials and rely on a long, slow secondary fermentation to produce the required level of condition.

Or you could add fermenting wort. Which the Gerrmans would call "kraeusening". This was a process favoured by many Irish brewers.