For the beer lover, no trip to Belgium is complete without a visit to the venerable Cantillon brewery, home to some of the world’s most famous Lambics and Gueuzes, sour beers that are certainly an acquired taste, but have the tendency to make serious beer geeks rhapsodise for days.

Ask brewers at the height of their profession, such as Evin O’Riordain of London’s The Kernel, who they’re inspired by, and the answer is Cantillon.

And so it was that a beautiful spring afternoon saw 300 Beers make something of a pilgrimage to 56, Rue Gheude in Brussels. Here’s the brewery itself, complete with matching van:

The brewery appears closed at first glance, but be brave and open the door, and you step into a time capsule full of evocative sights, sounds and, in particular, smells. Cantillon have been on this site since 1900, and it shows in the accumulated dust and cobwebs. The brewery remains resolutely family-owned, and brewing methods and equipment are virtually unchanged in generations.

You pay a few euros for the visit, including a self-guided tour and samples of two beers. After a brief orientation you’re handed a detailed pamphlet which explains the workings and history of the brewery, and then you’re left to wander around at your leisure.

You can take all the time you want, and even—as I did—go around twice if you wish. I was lucky enough to have the entire brewery to myself, apart from a couple of Cantillon workers manning the bottling line, and another chap studiously washing kegs. The latter task is perhaps one of the least glamorous yet most vital parts of any brewery’s operations.

The brewing process begins with the mash tun, where malted barley, wheat and steaming water are combined to make wort, a thick, porridgy stew full of fermentable sugars and other tasty goodness:

After being separated from the spent grain—known locally as “Draff”, which is used as animal feed—the resulting wort is pumped upstairs to the copper kettle, where it’s boiled with aged hops to sterilise and condense it, and to fill it with delicious hop resins:

After several hours of boiling, the wort is pumped up to the attic, where it’s left to cool overnight in a giant copper tray called a “coolship”. This is a crucial and unique part of the Cantillon process, as the attic is open to the elements, allowing the wort to become inoculated with wild yeast from the Brussels air. No yeast is added manually, and the wild yeast is what’s behind the distinctive sour flavour.

The next day, the cool, yeasty wort is drained into the stainless steel fermenter where, over several days, the sugars are turned into alcohol by those magic little yeast bugs, and the liquid starts to resemble beer.

I can’t for the life of me figure out how they got that wooden cart up into the attic.

Once fermented, the beer is transferred to decades-old wooden barrels and left to bide its time in the barrel store, where it is aged for up to three years before bottling. The smell in here is fantastic:

The barrel ageing produces a still, wine-like beer named Lambic, which is the base of all Cantillon products. You’ll have to come to the brewery to try it, though, as almost all of the Lambic is used to make Gueuze. This is a blend of one, two and three year-old Lambics, which are then refermented in the bottle in the brewery’s cellars to become the beers that are sold to the public.

Given the amount of time the beer needs in the barrel and subsequently in the bottle before it is ready, the biggest limiting factor to Cantillon’s output is storage space. The whole place is packed floor to ceiling with dusty bottles laid down. Every nook and cranny is utilised.

Finally, to the bar for a tasting. Visitors are given a taste of the still Lambic fresh from the barrel (left), and then allowed to choose a further beer to sample. I opted for the Kriek, a Gueuze in which sour cherries have been soaked for around six months, and then bought myself a glass of the classic Gueuze (right):

The Lambic is reminiscent of a high quality apple juice, albeit an unsweetened one made from sour apples, while the effervescent classic Gueuze is full of zesty grapefruit flavours.

If that isn’t enough sour beer for you, the brewery will happily sell you individual bottles or whole cases to take away with you, at prices significantly lower than you’ll find Cantillon products elsewhere, if you can find them at all. All told, a visit to Cantillon is a fascinating experience and quite a treat for the beer lover.