A famous marketing term used by Stroh's brewing in Detroit advertised "Fire-brewed" beer. But what does this mean? Fire brewed has to do with the type of heat source used in the brew kettle to boil wort (unfermented beer). Hence the name, "Fire-Brewed" means that there is a flame or gas burner underneath the kettle adding heat. In fact, Stroh's was the last large US brewery to have a direct fire brew kettle. This is a departure from the steam jacketing heat sources used in most brewing systems. Steam jacketing is a heating system that generates steam in a boiler and recirculates it through a piping system that transfers the heat from the steam to the contents of the kettle. Both systems have their advantages and disadvantages, not only in the effect on the beer brewed but with versatility and maintenance. We'll leave the design of the systems alone and focus on each heating system's effect on beer flavor.
The main difference between direct fire and steam jacketing is something called "boundary temperature" which is the temperature of the surface metal contacting the wort. Direct fire kettles generally have higher boundary temperatures than steam. The negative effect of high boundary temperatures is the increased production of precursors to esters. Esters are compounds that are recognized on your palate as fruity flavors, which are fine in some types of ales but not really in the lighter lager styles that Stroh's was producing. The advantage of the higher boundary temperatures produce by direct fired kettles, is increased caramelization. This carmelization produces a richer red color and sweeter flavor that would have been appropriate for the Stroh's style and would have differentiated their beer from their competitors at the time.
I confess I have never had a Stroh's, but BBC also has a direct fire system, so we sort of carry on the Fire-Brewed tradition
never trust The Sober Brewer