Belgian sours are the most amazingly complex beers in the world. Here are the ones to try

In the history of beer making, the use of isolated, cultivated strains of brewer's yeast to make beer is a relatively recent development. Before Louis Pasteur's late 19th-century discovery of brewer's yeast as a primary fermentation agent, its dynamics were not understood very well. Brewers controlled the process by adding active yeast from one batch into the next.

Beers allowed to age would let nature take its course and typically become inoculated with organisms from the surrounding environment. Bacteria and wild yeast made their way into the beer from the air and from the vessels in which it was stored, bringing a host of complex sour and funky flavors. Even into the 1700s in London, old porter that had begun to take on a bit of acidity was considered the good stuff.

As beermakers gained more control over the brewing process, the taste for funky, sour beers decreased. In most places, brewers worked to prevent such infection from occurring. But in Belgium, particularly in the Flanders region and the Senne River Valley around Brussels, the centuries-old method of spontaneous fermentation survived in the form of lambic and Flemish red and brown ales. These styles stand as some of the world's most beautifully complex beers.

Spontaneous fermentation means that beer is fermented without the brewer adding yeast. Organisms from the air, brewery walls or the wood of a storage vessel inoculate the beer, causing fermentation to start. Rather than a single strain of brewer's yeast, these beers rely on a cocktail of yeasts and bacteria to do the job. Each one puts its own mark on the beer, from fruity to acidic to barnyard funky.

Because the organisms work slowly and in succession, these beers take a long time to mature. Some at least a year; many two to three years or longer.

The lambics of Brussels

To brew the lambics of Brussels, inoculation is achieved by pumping the hot wort into a shallow trough called a "coolship" that's located in the brewery's attic, where it is left to cool overnight. Louvered walls allow the outside air to flow through, bringing microflora with it. As steam condenses on the ceiling, the falling droplets carry cultures built up over decades or even centuries of beermaking. Once cool, the beer is transferred to oak barrels for aging.

After three years in the barrel, the mature lambic may be bottled as is. Commonly though, it is blended with lambic that's one or two years old to make a beverage called gueuze. It can be aged further on fruits like cherries or raspberries. In any case, the bottles typically age for another year or more before being released.

Lambic blending is an art in Belgium. Brewers will commonly incorporate beers from other breweries into their finished blends. Oude Gueuze from 3 Fonteinen Lambiekbrouwerij is blended from five different barrels representing eight different brews: 30% is their own beer, with the remaining 70% coming from two other breweries. This beer is fermented bone dry, but still has a smooth, rich mouthfeel. Bready wheat malt provides a firm base for bright, tart acidity and peppery, barnyard funk. The peppery spice gives an increased impression of bitterness that lingers into a sour finish.

To make Oude Kriek, 3 Fonteinen aged young lambic on sour cherries for six months. The resulting beer is light and delicate. Tart pie cherries are the star with deeper, dark red cherries coming in as the beer warms. While the acidity and funk are present, both stay well behind the fruit. Bready wheat sits beneath, bringing a touch of sweetness to temper the tart. A touch of woody oak adds to the complexity.

Out of respect for the Senne River Valley's lambic brewing history, Brouwerij De Ranke in Dottignies, Belgium, calls its Mirakel gueuze a "Spierlambic" after the nearby Spier River. Mirakel is a blend of one-, two- and three-year-old lambics from three breweries, including two located in the Senne Valley. It's more funky than sour. Wheat is still a main player, giving a creamy smoothness to the mouthfeel and a bit of sweetness. Lactic and acetic acidity is present, but remains in the background behind the apple, pepper and horse blanket. This, along with the dry fermentation, makes this an easy-drinking refresher.

The ales of Flanders

There are nearly as many ways of making the red and brown ales of Flanders as there are breweries that make them. Some employ a coolship to spontaneously ferment a portion of the brew. Others start with a normal brewer's yeast fermentation in stainless-steel tanks.

Nearly all of them end up long-aging the beer in large oak tanks called foeders — some have been in use for more than 100 years. The foeders' porous wood hosts the cultures of wild yeast and bacteria that give them their sour and funk. After aging for 18 months or more, the beer is blended with fresh, unaged beer to create the finished product.

Known as the "Burgundy of Belgium," the Flemish red and brown ales are beers for wine drinkers. Less sour and funky than lambic and gueuze, they make a good introduction to Belgian sour beers.

In the red ale category, the benchmark is Rodenbach Grand Cru. This must-try beer is a blend of 70% aged beer and 30% new. It delivers dark cherry and balsamic vinegar notes that are characteristic of the style accompanied by vanilla and oaky tannins. It's vinous and tart, but with enough residual malt to keep it balanced and beer-like. The lighter Rodenbach Classic is a 75-25% blend of new beer to old. It has a similar profile as the Grand Cru, but with less intense barrel character.

The first time I tasted Duchesse de Bourgogne from Brouwerij Verhaeghe, I turned to the person next to me and said, "This is delightful." Somewhat sweeter and fruitier, it is a great introduction to the style. The wild yeast character dominates, creating an intensely fruity beer with notes of plum, red currant, apple and dark cherry. Balsamic sourness plays a supporting role. It's all enveloped in a softly sweet blanket of caramel malt.

Bourgogne de Flandres from the Bourgogne de Flandres Brouwerij in Brugge is a new favorite of the style. It's very fruity, with dark cherry and raisin in abundance. Plum and chocolate also appear along with hints of toasted grain and caramel. While the balsamic flavor is there, it doesn't come off as particularly sour. Smooth, delicious and easy to drink, it changes with every sip.

Vanderghinste from Brouwerij Omer Vander Ghinste is a great example of how delightfully complex an everyday beer can and should be. Raisiny malt is the main driver in this Flemish brown ale, along with notes of toasted grain and caramel. Light acidity layers onto the malt, leaving an impression of sourness without being puckering. Black cherry, red apple and just the right amount of barnyard round it out.

Old beer, new twist

Though steeped in tradition, the sour beer brewers of Belgium are not averse to innovation. Brouwerij Timmermans is the world's oldest lambic brewery — they've been making lambic there for more than 300 years. In collaboration with Guinness, it produces a unique blend called Lambic & Stout. My first note on tasting this was "YUMMY!" It's a beautiful melding of roast and sour — like dark chocolate brownies with a tart, fruity twist. The stout has the slight upper hand, bringing chocolate, burnt roast and a touch of caramel that intensifies as it warms. The lambic comes with pineapple, apple, cherry, sour and funk that both complements and contrasts.

With Timmermans' Lambicus Blanche, what's old is new again. A blend of lambic and Belgian witbier, Lambicus Blanche is, according to the brewery, beer as it was once brewed on the farms of Pajottenland. The bready wheat, orange peel and coriander of the witbier are all there, along with subtle hints of banana and clove. The lambic plays beneath with a delicious, bright acidity. Hints of barnyard are a nice complement to the coriander and clove. This is delicious.

Michael Agnew is a certified cicerone (beer-world version of sommelier) and owner of A Perfect Pint. He conducts private and corporate beer tasting events in the Twin Cities, and can be reached at michael@aperfectpint.net.