Belgium's centuries-old craft beers are favourites

Winding between copper vats and oak barrels, a cluster of early morning visitors filed through a cavernous Brussels building for an up-close peek at craft beers brewed using a centuries-old method - before sampling the result.

Since it was founded in 1900 in Anderlecht, a working-class district of the Belgian capital, Brasserie Cantillon has been turning out so-called primitive "lambic" beers that are steeped in local tradition.

What makes lambics special is they start with a process known as spontaneous fermentation - through exposure to wild yeasts, specifically those native to Belgium's Zenne valley - as opposed to cultivated brewer's yeast.

Aged in wood barrels for months to years, which allows for a secondary fermentation to occur as the beer's sugars convert to carbon dioxide, the result is a distinctive dry beer with a faintly tart aftertaste.

Cantillon's speciality is an even more niche type of beer known as "gueuze" - a blend of lambics from different years and whose fruity varieties include kriek, or cherry in Flemish - that has around 20 brewers in Belgium.