I found a very interesting description of the brewing process of Gose in Goslar from 1762 written by the physician Johann Friedrich Zückert.
In Summary he says:
The brewer has 4 fired Pans ("Pfannen"), one wooden lautering ton ("Sey-Butte") and one wooden mashing ton ("Mast-Butte").
The lautering ton has a floor from wooden logs which are covered with long ryestraw.
At one brewday they will produce 6 different Worts:
one that is lower in extract (1/3 of the malt 2 pans of water) and not lautered (only drained through baskets) but boiled with Hops for 2 hours ("Hopfkrug")
the others are boiled without hops:
one that is made from the same mash as the hopped one (probably higher in extract due to over 2 hours mash) ("Allerley-Krug")
The strongest one that is mashed in the lautering ton for 4 hours + (2/3 of the malt 2 pans of water). ("der beste Krug")
This one is stored in open containers, not in the cellar as the others.
(koolship-like method for spontaneous fermentation)
one that is composed of the last portion of the first runnings from the mash- and lautering ton. ("Vierpfannenbier")
one that is made from a second mash combined with all the grains from the 2 tons and some fresh malt and only boiled for one hour. ("letzte Wert")
one that is made by sparging cold water through all the grains. ("Süppie" or Cosent)
These different Worts (except the last one) are blended in different ratios depending on the designation of the beer.
Beer that will be consumed young will get more of the hopped wort.
By blending they produce ordinary Gose ("gemeine Gose").
The blended wort is fermented in the cellar in wooden barrels, there is no yeast pitched.
Fermentation is ready within 12 to 24 hours. (unclear if its finished to be consumed or beginning of kräusen)
The strongest wort alone makes beer that is too strong to be consumed.
The second strongest ("Vierpfannenbier") is consumed as delicacy as it is stronger than the ordinary Gose.
The others are weaker than the ordinary Gose.
They are drunk by the poor people.
Thats how Gose is described in the text:
Color is yellow like beeswax
Cloudy from yeast
It has a thick foam that sticks to the glass
taste is severe, winelike and slightly bitter
those who don't know it call it unpleasant, those who know it can tell a nice sweet taste.
very good for beersoups (because of the winelike aroma)
the beer is cloudy from the yeast because they drank it fresh in fermentation. when fermentation is completed it will be clear like every beer but it is sour like vinegar.
Therefore it cant be transported longer distances.
In the summer it can be conserved for 14 days in the winter for longer.
When it is fermented in a closed secondary fermentation it will be of very high alcohol.
They also have a brown beer ("Braunbier") in Goslar.
Pale brown color, made of Barley without use of kiln-malt. It is called "Lager-Bier".
The text notes about Broyhan: It is pleasantly sweetish and light. Also yeasty.
My conclusions for Goslarer Gose of the time:
- it was spontaneously fermented much like lambics are today
- there was wheat in it (text tells nothing more than that)
- Probably there was a good portion of acetic acid bacteria. (that would allow a secondary fermentation if kept from oxygen)
- it was probably of relatively high extract (15°?) but drunk before end of fermentation
- It was probably well hopped to contrast the sweetness together with the sourness.