At the same time, lager brewing was becoming more common in Europe, especially in southern Germany and Bohemia. Lagerbiers were considered intrusive and, additionally, brewers in the Rhineland found that conditions were not optimal much of the year for bottom-fermentation. Substandard beers were simply not going to pass muster with the guild and, to that end, bottom-fermentation was outlawed in Köln in 1603. Top-fermentation is still a mandate of modern Kölschbier.
While stylistic kölschbier was taking shape in the seventeenth and eighteenth century, it had much in common with traditional altbiers, as pale malt had not yet been developed. The invention in 1818 of the indirect heat kiln as a device to dry and color malt was perhaps the greatest modern event to influence brewing. This continuum of malt color, including the very palest, quickly led to an explosion of experimentation with malt combinations and the birth of numerous beer styles. Golden pilsner, first brewed in 1842 in Bohemia, sparked a Europe-wide brewing revolution. Pale lagers were everywhere, often muscling aside indigenous and regional artisan brews.
Köln was protected by the prohibition of bottom-fermentation, but the popularity of golden beer led them to acquiesce, furthering the design of a new and unique brew. For the most part, only brewers in Köln and Düsseldorf, 45 km to the north, were brewing top-fermented barley ales in the nineteenth century. The paler brews of Köln were described as being “golden in color, highly hopped, and 8 to 9 degrees Plato (OG 1.032 to 1.036). The Düsseldorf brews continued to use the darker Munich-style malt for a full copper color. Since refrigeration was now possible, altbier and Kölsch brewers adopted cold-conditioning, perhaps to ensure customers that smooth, refined character that they had come to expect, and also as a commercially viable means to store beer safely after fermentation. Both became known as obergaerige laberbier (top-fermented, cold-conditioned beer).
Until the late nineteenth century, “Kölsch” was not used to designate a style, but an adjective for a something emanating from Köln. By the turn of the twentieth century, there was a distinct style of beer coming out of Köln. Kölsch as a stand-alone label was adopted by the Brauerei Sünner in 1918 to describe the beer that they had been making since 1906. The style designation was born, and used thereafter by other breweries in the city. Filtered versions were often called echt Kölsch or genuine Kölsch, with the unfiltered examples known as wiess or white because of their turbid shimmer. It may have contained as much as 20 percent wheat.