Buy Sourbier at ’t Bockje Bathmen

Ordinary beer is fermented by a yeast the brewer adds himself. With sour beer, wild yeasts and lactic acid bacteria take over the work. That produces acidity rather than just alcohol, and with it a beer that is more reminiscent of cider or white wine than of pilsner.

The oldest form is lambic from the Senne valley near Brussels: the wort stands open overnight in a coolship, catches whatever is in the air and then matures for years in oak casks. A gueuze is a blend of young and old lambic that referments in the bottle. If sour cherries or raspberries are added, it is called kriek or framboise. Faro is lambic with candi sugar.

Then there is the Flemish school: red-brown from West Flanders and oud bruin from East Flanders, matured in large wooden casks and then blended with young beer. German beers work differently: Berliner Weisse and Gose are light, salty or spicy and quickly ready.

The new approach is called kettle sour. The brewer lets lactic acid bacteria do their work in the brew kettle for a day, then boils and continues brewing. It takes weeks instead of years, and so it is found at brewers who have no barrel cellar.

Serve sour beer cool, around six to eight degrees, in a tulip glass or a goblet. An Oude Geuze can also be a little less cold; that brings out the wood. Sour beer goes well with fat and salt: with a mature cheese, with mussels, or with a stew that the beer itself went into.