Steam beer is a process, not any one particular recipe IMO.
This is where I have landed based on what I have read. Beer historian Martyn Cornell has a recent very well-researched article on his website:
Steam beer from Yukon to Nevada and the strange link with Flat Beer
I love this passage:
Skagway steam beer, “light or dark”, was served at a table in a glass pitcher containing a quart of beer, for 25 cents. It was “produced and consumed at high speed. No one expected quality and no one found it.”
The fact that it was available "light or dark" tells me that it was more a way of brewing or serving, not a specific style or color.
"The beer is sold in two varieties, as
flat beer [sic] and as
steam beer. However,
both come from the same brew and their difference only arises when they are filled into the barrels. The flat beer is the usual draught beer. The steam beer, which is purchased in smaller quantities, receives an admixture of young beer from the fermenting vat when it is filled up, namely as the first entry into the barrels. This young beer is then processed with the flat beer and brings it into powerful fermentation. When pouring, the glasses are filled up to a third with steam beer and the rest with flat beer, which mixture provides the guest with a clear, active beer with a delicate, milk-white foam." [emphasis mine]
The important difference was kräusening: "No contemporary source gives an explanation for the name “steam beer”, but the evidence strongly points towards the high condition that the beer was in because of the krausening."
Gary Gillman published an
8-part series which states that it is (1) the way the beer is clarified and (2) the kräusening that are key, not the ingredients or type of yeast, since there is evidence for both ale and lager yeasts being used.
This other post quotes the above-mentioned 1903 article:
"Materials used are either malt alone or malt and flakes. Some brewers use rice or grits in conjunction with malt. Glucose is also used in small quantities. Hops are nearly all Pacific coast hops. The malt for steam beer brewing is usually somewhat darker than lager beer malt."
I think my Vienna lager that I just kräusened and kegged today probably isn't too far off (except that I fermented at 50F and used Saaz hops).