It seems that this change was at least partly due to the switch in taxation from malt to the OG of the wort before fermentation. A change which had only taken place a few years earlier, in 1880.
"For instance, since the abandonment of the malt duty, types of grain have come into use and methods of malting have been carried out that have led insensibly to the production of infusion worts almost entirely destitute of dextrine, or, at any rate, of dextrine in sufficient quantity to determine that persistent palate of beer that is thought so necessary, while as public taste has been drifting in the direction of a decided preference for low gravity beers in place of those of extreme body and strength, that were indeed so diligently sought after a few years ago, this question of infusion extract and its general composition has of necessity become more and more important."
"The Theory and Practice of Modern Brewing" by Frank Faulkner, 1888, page vi.
By "types of grain" I think he's talking about unmalted grains, such as flaked maize and flaked rice. Which I doubt produced much dextrine.
It's funny when he talks about the low-gravity that drinkers now prefer. These wouldn't be what we would consider low-gravity nowadays. The would have been at least 1050º.
The typical dextrine content of wort had about halved, from 20-22% to 10-12%. Quite a big change.
"It is well known, I think, that the theoretical transformation products of malt starch (or rather of malt extract) contain, as a rule, about 60 or 62 per cent, of maltose and 20 or 22 per cent, of dextrine, while for reasons in connection with altered character of material, the adoption of low infusion heats, subdivision of mash wort, and stewing during collection process, this theoretically normal composition of wort extract is no longer very common, the ordinary dextrine constituent in the case of infusion worts having diminished to a proportion not exceeding, as a rule, some 10 or 12 per cent, upon total solids.
I am not saying or wishing my readers to infer for a moment that the dextrinous bodies are the sole constituents of wort capable of communicating body, viscidity, or foaming capacity to resulting beer; but they are, at any rate, of very great importance, the exact percentage in which they exist having much to do not only with the condition of beer, but the way in which it matures during lengthy storage."
"The Theory and Practice of Modern Brewing" by Frank Faulkner, 1888, page vi.
The decline in the public's enthusiasm for aged beer would also have had an effect. Beers served no more than a couple of weeks after racking didn't need a high dextrine content to provide fuel for the secondary fermentation.


