Not sure who or what R.S.O. was. But they recommended this method:
"III. Method. - R. S. O. shares the following procedure in the "Klein- u. Mittelbrauer":
Mash in at 5 o'clock at 28° R. [35º C], at 6 o'clock it is 35° [43.75º C], at 7 o'clock 44° [55º C], at 7:30 48° R. [60º C]; at this temperature there is a rest of 0.5 hours; Then go up at 8:30 to 54º R [67.5º C] and at 9 o'clock to 62º R [77.5º C], then let down 2/3 of the mash into the lauter tun (which must be preheated beforehand with hot water), bring what remains in the pan quickly to the boil, which lasts, according to wishes, 5-20 minutes, and immediately mash out at 61º R [76.25º C]. The wort should run off crystal clear and its flow should not be interrupted."
"Die Fabrikation obergäriger Biere in Praxis und Theorie" by Braumeister Grenell, 1907, page 72. (My translation.)
As you can see this method consisted of a step mash and a short boil of two-thirds of the mash. I assume that the boiled mash was added back to the main mash in the lauter tun to hit the mash out temperature of 76.25º C.
And here is the final method. Bet you’re glad that we’re done, aren’t you?
“IV. Method. Sometimes the following infusion method is also used:
Mash in in the pan at 28-30° R [35-37.5º C], and mash for half an hour while stirring continuously with the fire covered; then it is slowly heated in 1.25 hours to 51-52 ° R. [63.75-65º C], and 1 pound of hops per Zentner [50 kg] of malt are added, Then the wort is left to rest for 30 minutes, then heated to 61-62° R [76.25-77.5º C], and then left in the mash and lauter tun, where the mash itself reaches a temperature of 60° [75º C]. Continue then as per method II.
The method with boiling is, of course, much more reliable, although boiling has no influence on the character of the beer. Take care that at mash out a temperature of 61-62º [76.25-77.5º C] is maintained (at which all the germs and bacteria are rendered harmless), the method I is also recommended for rapid cooling, as well as for the immediate pitching of yeast.
If one has to struggle with "difficulties" in the clarification in bottles, the first wort and sparge are pumped into the kettle and there, during run off, the temperature is held at 78-80 ° R [97.5-100º C]. In case of "irregular fermentation", one reverts to boiling the wort.
The bottles are difficult to keep clean to avoid a "thread pull" (ropey beer), which often occurs in the summer.
As a fairly high amount of wheat is employed, the "run off" takes more time (5-6 hours); if the run off is too quick, the sediment will sit too fast. It is also not always appropriate, especially in the case of a fine grist, to sparge immediately after mashing out, in order to avoid clogging the holes in the false bottom. Here the use of a mash filter is recommended.
"Die Fabrikation obergäriger Biere in Praxis und Theorie" by Braumeister Grenell, 1907, pages 72 - 73. (My translation.)
Interesting what Grenell counts as an infusion mash. Because there are still several different mash temperatures and a rest. I assume it’s infusion because there is no boiling of the wort. Though it does recommend holding the wort at just about boiling point during run off if there are problems with clarification.
These last two paragraphs seem to refer to Berliner Weisse in general, rather than to method IV in particular.:
“In the summer, when the carbonic acid content is too low, often 500 gr. of cooking sugar is added per barrel, too.
Weissbier requires a careful final handling by the publican, as otherwise the quality of the beer suffers a lot. But since nowadays every one becomes a landlord, and very seldom understands something from the handling of the beer, sales have been decreasing.”
"Die Fabrikation obergäriger Biere in Praxis und Theorie" by Braumeister Grenell, 1907, page 73. (My translation.)
Not sure why the CO2 content would be too low in summer. Surely there would be a more lively fermentation in warm weather?
That final comment could just as well be talking about cask beer in the UK. Just like cask beer, a lot of the old German top-fermenting styles were sent out to pubs before fermentation was complete. The final stage needed to be completed by the publican. I’m sure there were plenty of ways he could cock things up.