The Foss Brewery (Norwegian: Foss Bryggeri) was a brewery in Oslo. The company was started in 1836 as the Ytteborg Brewery (Ytteborgs Bryggeri) and was located on Hausmanns gate (Hausmann Street). In the 19th century, the water in the lower part of the Aker River became too contaminated to brew beer, and the brewery needed more space. Therefore in 1897 the brewery relocated to new premises further upriver, above the town's Grünerløkka district at Upper Falls (Øvre Foss)—one of two waterfalls forming Vøyen Falls (Vøyenfallene, Vøyenfoss). The company also changed its name to Foss Bryggeri (literally, 'Falls Brewery') to reflect the new location.
The Ytteborg Brewery was founded by Nils Jensen Ytteborg in Christiania i 1836, with cellars below Old Aker Church. The Ytteborg Brewery was especially well-known for its Bavarian beer. After the operations were relocated upriver in 1897, the old cellars were used for various purposes, including vegetable storage during the Second World War. The cellars started deteriorating in the 1950s, when the cemetery at the church was expanded.
In 1897, the brewery built a large factory at Vøyen Falls, where a brick factory (Øvre Foss teglverk or Foss teglverk) had been located, at what is today the level area and parking space between the old Ringnes Brewery and the Aker River. At the same time, the company changed its name to Aktieselskabet Foss Bryggeri. The address of the company was Thorvald Meyers gate (Thorvald Meyer Street) no. 9.
The new brewery continued to use the old cellars at Old Aker Church, but later built its own cellars next to the new factory. The Foss Brewery was headed by Carl Theodor Ytteborg, who was the son of the original brewery's founder. The Foss Brewery produced the brands Bayersk Øl and Pilsener Øl, as well as Lands Øl, Bok Øl, Malt Øl, Vørter Øl, Kulmbacher Øl, Lager Øl, and Salvator Øl (launched on March 14, 1899). The brewery was very successful, and it expanded its production facilities. In 1899 it purchased the venue on Oslogate (Oslo Street) where the restaurant Oslo Spiseforretning is now located, and in 1900 it built the Hotel Continental and Theatercaféen restaurant, which the brewery leased to various restaurateurs.