Cantillon's Jean Van Roy got the idea for the use of the Brussels cellars in the centre of the city after visiting wine cellars in France.
The water basin of the River Zenne on which Brussels is located used to be situated along the Hooikaai. Later this was vaulted over and turned into a cellar that was used as a bunker during the last war with Germany.
So far 8,000 bottles have been placed in the cellars, but their number is set to grow. Temperature and humidity levels under the centre of Brussels are thought to be perfect for fermentation of the beer.
What exactly is Lambic?
Wikipedia explains it as follows:
Lambic is a very distinctive type of beer brewed only in the Pajottenland region of Belgium (southwest of Brussels) and in Brussels itself at the Cantillon Brewery and museum. Lambic is now mainly consumed after re-fermentation, resulting in derived beers such as Geuze or Kriek.
Unlike conventional ales and lagers, which are fermented by carefully cultivated strains of brewer's yeasts, Lambic beer is produced by spontaneous fermentation: it is exposed to the wild yeasts and bacteria that are said to be native to the Zenne valley, in which Brussels lies. It is this unusual process which gives the beer its distinctive flavour: dry, vinous, and cidery, usually with a sour aftertaste.