Henri Vandervelden, who at the time was working for Brouwerij De Kroon in Uccle during the cold months and as a fruit buyer and picker during the warmer months, started construction of his own brewery with the help of local brick fabricators. His experience at De Kroon, that at the time specialized in producing various lambics, gave him the necessary skills to continue on with his own brewery. When Henri’s son Egidius married Catharina Hofmans, the groundwork was laid to expand the Hofmans’ family farm and turn it into an actual brewery. In 1922 Egidius set out to update and upgrade equipment in order to begin producing beers. In the meantime, Egidius’ younger brother Pierre Vandervelden continued his father’s blending and brewing business until shortly after World War II ended.<ref name=“GeuzeKriek”>Jef Van den Steen, [[Books#Geuze & Kriek: The Secret of Lambic Beer|Geuze & Kriek: The Secret of Lambic Beer]], 2012</ref>
The brewery that Egidius set up was not initially a lambic brewery, though it produced lambic-esque beers. In many ways, Egidius was the first to establish a non-traditional lambic. By 1930, he was the first to produce a sweetened, pasteurized Kriek in bottles with a crown and a cap.<ref name=“OudBeerselHistory”> Oud Beersel History (Dutch), http://www.oudbeersel.com/brouwerij/historie/ </ref><ref name=“GeuzeKriek”>Jef Van den Steen, [[Books#Geuze & Kriek: The Secret of Lambic Beer|Geuze & Kriek: The Secret of Lambic Beer]], 2012</ref> Lambic was not produced at Oud Beersel until shortly before World Ware War II started using old second-hand equipment. The production was halted when, at the order of the occupying forces, brewers were not permitted to use wheat in their beers. As a replacement, Egidius began to brew a low-alcohol beer using ground-up and dried sugar beet and some hops.<ref name=“GeuzeKriek”>Jef Van den Steen, [[Books#Geuze & Kriek: The Secret of Lambic Beer|Geuze & Kriek: The Secret of Lambic Beer]], 2012</ref> Egidius passed away at a young age in 1953 leaving the brewery to his son Henri Vandervelden II.
Henri II graduated from the Institut National des Industries de Fermentation in 1948 and already had first hand knowledge of the brewing process when he took over after Egidius’ death. He immediately made a move to expand production capacity to 50 hectoliters (approximately 42bbls); the volume that Oud Beersel would continue to produce until it closed for the first time in 2002. Upon taking over the brewery, Van den Steen writes, Henri II chose the name Oud Beersel to “emphasize the artisanal, traditional character of his brewery and also to distinguish himself from what he refers to as ‘New Brussels’.<ref name=“GeuzeKriek”>Jef Van den Steen, [[Books#Geuze & Kriek: The Secret of Lambic Beer|Geuze & Kriek: The Secret of Lambic Beer]], 2012</ref> With the production of lambic restored at Oud Beersel Henri II turned the brewery into the first living lambic museum in 1973. In 1981, Oud Beersel won high accolades from the consumer group Test Aankoop for not only producing excellent lambic, but also by being one of the first producers to stop sweetening their lambics with saccharin. <ref name=“GeuzeKriek”>Jef Van den Steen, [[Books#Geuze & Kriek: The Secret of Lambic Beer|Geuze & Kriek: The Secret of Lambic Beer]], 2012</ref> <ref name=“OudBeerselHistory”> Oud Beersel History (Dutch), http://www.oudbeersel.com/brouwerij/historie/</ref>