BRUSSELS -- Beer is usually not a morning pursuit.

But it was still dark one day last month when I lumbered out of bed and over to the tiny Cantillon brewery, located in a scruffy neighborhood not far from the main train station here.

Industrial brewers can be as secretive as defense contractors -- good luck getting inside the mashing room of Diageo PLC's Guinness brewery in Dublin -- but a couple of times a year Cantillon opens its doors to the public.

I had risen early because I wanted to see how to brew lambic, a Belgian specialty so retro its origins go back thousands of years. The early-morning start was necessary because there are no refrigerated tanks or cryogenic chillers at Cantillon; the boiled liquid that will become beer cools in the open air, and it needs a whole, cold night to do so. Thus all the mixing, cooking, filtering and boiling must be completed well before sunset.

Lambic brewing is "a process that has become so rare around the world, but that was once the universal method of making beer," says Jean-Pierre Van Roy, the patriarch of the family that has owned and run Cantillon for a century. "As with everything rare, we need to be watchful, we need to be able to show this type of industry to our generation and future generations."