The text below confirms some of the odder characteristics of Berliner Weisse. Namely that it was originally brewed using smoked wheat malt and that it was often watered down at bottling time. Also, that there was a Märzen-strength version.
I’ll let Grenell explain further.
Original gravity: 12%, Märzen: 15-15% balling.
Berliner Weisse is a very refreshing, highly-carbonated, slightly sour drink, and is particularly enjoyed in the summer mixed with fruit juice.
As it is produced nowadays, it is quite different from the old version, as in the past a smoked wheat malt was used, the yeast changed after every third brew, and a new batch brought from Cottbus; furthermore, in the middle of the last century, Weissbier was usually sold as a young beer, shipped immediately to publicans, and further fermented by them, and then bottled with some barm, with a little water added, and therefore they were called Ganz- or Vollweisse [whole or full Weisse]. Heavily watered beer was delivered as Halbweisse [half Weisse] at a cheap price.
The brewing process is similar to Einfachbier. 3 parts of wheat malt and 1 part of barley malt or 2/3 of wheat malt and 1/3 barley malt are used. Both malts, on account of the different grain sizes, are milled separately, and the wheat malt, for a better yield, is milled finer; additionally the malt is mostly assembled in bins the day before, and lightly sprinkled (with 1-2% of water) in order to make the husks crush more easily. However, the wheat malt itself is to be kept dry.
In the authentic brewing process the wort is not boiled, but is mashed in at 61-62° R. [76.25º - 77.5º C], pumped directly from a grant to the cooler, and left there for as short a time as possible, the best way to do this is to let it flow through the cooler and then over the chilling apparatus into a large pitching tun.
The hop charge of 375-500 gr. Per Zentner [50 kg] of malt is boiled for 5 minutes before mashing in the mash tun and then used with the brewing water to brew the mash, that is, cold water is added to bring the whole mash to 28° R [35º C] h and the quantity is calculated so as to produce 1 hectolitre of original wort per Zentner [50 kg] of malt. It is mashed at the above temperature with the rakes moving constantly.
The mash out temperature of 61-61° R. [76.25º - 76.25º C] is necessary, if one does not wish to run a great danger of infection; however, one should not go higher in order not to weaken the "diastase" too much and thus prevent saccharification. The lauter tun should, of course, be well insulated compound in order to prevent it cooling. Once the wort is in the pitching tun it should be immediately pitched yeast!”
"Die Fabrikation obergäriger Biere in Praxis und Theorie" by Braumeister Grenell, 1907, pages 68 - 70. (My translation.)
Not boiling the wort was typical of 20th-century Berliner Weisse production. Partly to keep the colour of the finished beer incredibly pale. You can see why that would form a risk of infection, hence the care taken to quickly cool and pitch the wort with yeast.
A ratio to two parts wheat malt to one of barley is the classic grist, but by no means fixed. There were even versions without any wheat at all sometimes in the 20th century. Which is a bit of a cheek. Though that was Kindl and their Berliner Weisse always was crap.
The current incarnation of Berliner Weisse at only Schankbier (8º Plato) strength is fairly recent. Stronger versions existed in the 20th century. Not sure when they disappeared, but the post-war DDR-brewed Märzen-Weisse was Märzen in name only, still being Schankbier strength.