Flanders Sour Brown Ale

March 1, 2002 By Randy Mosher

Sometimes, one sip of a beer can transport you back through the centuries, a sort of liquid time machine. The sour beer of Flanders, with its unique tangy, fruity aroma, magical ruby color, and refreshing yet earthy taste, can do just that.

This archaic beer style will take you to a time when stainless steel was just a twinkle in an alchemist’s eye, back a couple of hundred years, at least, to when wood was the only practical material available for constructing fermentation vessels. What you get with wood fermenters, along with a high load of maintenance obligations, is a zoo of little creatures that snuggle in and use the beer as their own personal picnic grounds. This can be a nightmare if it goes wrong, but such microbial colonies can at times be wholly elegant, adding a profound, earthy perfume to the brew, plus lactic and acetic acids that overlay a quenching tartness

Present commercial versions of the Flanders sour beer style are made with a small proportion—less than 25 percent—of soured beer, blended into a batch fresh from a few weeks’ fermentation. This dilutes the overwhelming sourness of the aged beer and, of course, adds complexity.

Some sources draw a distinction between the East and West Flanders versions of this beer type, the West Flanders variant generally the sharper tasting. But to me, the differences seem less important than the similarities. Once, such beers were plentiful in Flanders; today, only a few remain. In a situation in which the number of producers is greatly reduced, the big picture gets distorted and the idiosyncrasies of brewers that remain get magnified beyond their importance as far as the original style is concerned.

Flanders Specifications

Gravity is modest at 1045 to 1050, although stronger versions are possible. Color should be a rich reddish brown. Hopping is light, as with most types of sour beers, with no detectable hop aroma. The palate should be dry, with a very soft, malty roastiness balanced against the acidity.

Because of their simple malt/hop profile and bright acidity, these beers make great bases for fruit beers, with cherries and raspberries being preferred.

Brewing is straightforward; a simple infusion mash is adequate. Relatively low mash temperatures should be used, as this promotes the kind of enzymatic activity that creates a highly fermentable wort, which in turn creates a crisp, dryish beer. This is a good beer to brew from extract, with augmentation from some crystal malt.

Only one essential detail remains: how to get it to turn sour. I have had good results from the Wyeast mixed lambic culture, added after primary fermentation is complete. These critters are rather slow at the smorgasbord, so expect to wait a few months before you get much effect from them. I would let them have at it for maybe three months, then have a taste.

As mentioned, oak vessels are traditional. And at Rodenbach, at least, the barrels are scraped to expose fresh wood between every brew. In addition to being a good home for acetobacteria, especially, oak ultimately imparts a soft vanilla character, the result of the metamorphosis of lignin in the wood into vanillin.

Wood for the Homebrewer

Wood in the home brewery can be difficult to manage, but there are some shortcuts. Besides, wood isn’t absolutely essential to get you into the ballpark with this style, and I do recommend brewing one batch of this even if you don’t feel like messing with oak.

The most manageable solution is to use small oak cubes manufactured for the wine industry by StaVin (www.stavin.com). The company produces French, Hungarian and American oak cubes, about 3/8 of an inch on a side. These are intended to refresh tired wine barrels but will suit our purposes nicely. They come in several degrees of toastiness, packaged in sanitized foil packs. I personally haven’t had a chance to experiment with them, but next time, I’m going for French oak, with a light toast. A small handful will suffice. American oak will be far too pungent for beer use, except for massive brews.

On the other hand, you can go to extremes. I know an amazingly dedicated homebrewer who keeps a 50-gallon barrel of the brew going, withdrawing beer when he has fresh beer to add, in much the same manner as a sherry solera. This is beyond the reach of most of us individually, but it might be a rocking good idea for a club.

Flavorings

If you choose to use this brew as a base for fruit beer, ferment through the primary, then rack into a secondary onto plenty of fruit. Use at least 1 pound per gallon of cherries, half that for raspberries, although you could easily double those quantities and not have too much. I like to use fruit that has been frozen, as this lightens the microbial load a bit, but more importantly, breaks down the cell walls to make the sugars more accessible to the yeast. I also prefer cherries with pits, as they add a certain almond/kirsch complexity. Sour pie cherries are generally better than an eating type (such as bing) for intensity of flavor.

My own method is to do the secondary in a glass carboy, filling it with beer and fruit up to just below where the jug neck narrows. I find that this reduces the surface exposed to air, and thereby reduces the likelihood of mold developing. At the same time, this leaves enough headroom to prevent a piece of fruit from blocking the stopper hole, which can cause enough pressure to develop that it can explode the carboy (it has happened!).

Let the beer sit on the fruit for one to four months, rack into a carboy, and allow to settle before bottling or kegging.