"Beers consumed quickly may, however, be safely given a species of cask-fermentation, by adding to them some sort of fermentable sugar in solution. Such additions as these are termed priming, and it is customary to add them in the form of a syrup of about 1150 sp. gr., of which the Excise permit the employment at the rate of two quarts per barrel of beer. The sugars generally employed for this purpose, are invert sugar, glucose, and cane-sugar ; of these, invert-sugar is the favourite, as, in addition to ready-fermentability, it imparts during the early stages, a luscious sweetness which confers an apparent extra gravity on the beer. Glucose is also used, but more particularly in pale ales, where a dry flavour is more desired than the sweet fulness of invert-sugar. The very appreciable amount of unfermentable matter contained in glucoses, however, renders them less suited for priming purposes than arc invert-sugars. Cane-sugar is not often used as priming except in stout and porter brewing. The fermentation of the priming sugar throws no burden upon the secondary yeasts, since it is readily fermentable at the instance of the residuary primary yeasts ; it is at any rate a form of cask-fermentation which can always be relied upon, generally making its appearance within three or four days of the addition of the sugar. In the case of running mild ales the priming is added as a rule to the settling square; thus saving time and labour, and sufficiently answering the purpose for such beers as these, especially where the trade is a quick and uniform one. In the case of pale ales, or superior ales generally, it is best to add the priming to each individual cask just before it is sent out into the trade. By so doing, the customer gets the beer at its best, and with moderately quick draught the after-fermentation, due to the priming, will last out the required time. If in these cases the priming were added to the settling back, it would probably be all over by the time the beer was required in the trade. Priming solutions should always be boiled ; they should be made with the purest material, and made fresh at least once a week in winter, and every three days in summer.
Some brewers prefer rather to assist the yeast in degrading the maltodextrins into maltose, than to add extra fermentable sugar. To do this they add to the beer a small quantity of cold-water extract of malt, which, containing active diastase, will supplement the action of the secondary yeasts in degrading the maltodextrins. Only a small quantity needs to be used ; larger quantities would produce too rapid a removal of the maltodextrins, and this excessively early disappearance would be obviously dangerous in regard to the stability of the beer. Pale ales will stand one pint of concentrated extract per one hundred barrels of beer, added at racking; running ales double that amount.* The condition produced in this way is a steadier and more lasting condition than that produced by priming, and it is in most respects preferable to it. It depends, however, upon having a sufficiency of maltodcxtrin naturally present; priming, on the other hand, is independent of this. When the extract cannot be conveniently added to the beer in racking vessel, it may be added to the individual casks. In that case, it is previously diluted with beer to such an extent as to permit of the quantity due to each cask being sufficiently appreciable to be conveniently measured.
* Take two parts by weight ground pale malt, five parts by weight cold water; soak for six hours, stir periodically, then strain off and filter the solution through flannel. One pint of the solution to be used as above staled for too barrels of pale ale, and one quart to the same amount of running ale. The extract to be made fresh on each occasion. The grains are to be discarded."
"A text-book of the science of brewing" by Edward Ralph Moritz, George Harris Morris, 1891, pages 403 - 405.
Right, glucose, invert sugar and cane sugar are the favourite primings. With invert being the most popular and can sugar only being used for Porter and Stout. Not much very surprising there.