The secret of spontaneous fermentation

Lambic is the oldest of all modern beer styles. Typical for this blonde beer is the sour taste as a result of being exposed to wild yeasts and bacteria in the open air of the Zenne valley near Brussels. This technique is known as spontaneous fermentation.


Lambic is very different from any other beer style. It is generally brewed from a grist containing at least  30% of unmalted wheat. According to traditional methods, the brewer will also use aged instead of fresh hops. These hops have lost their bitterness and do not add much aroma or flavour to the beer. They will however make the beer very preservable.

Another important difference with other beer styles is that after cooking, the wort is brought to the huge cooling tray also known as a coolship. This is the most mysterious part of the brewing process. The wort is cooled overnight in the open air allowing the wind and local microflora to inoculate wild yeast into the wort. This process is only possible between October and May. During the warmer summer months unfavorable organisms could have a negative influence on the brewing process and the flavor of the beer.

After cooling, the wort is pumped into large oak barrels (foeders) to finish fermentation and the wort slowly turns into lambic. The beer stays in the foeders during 1 to 4 years. In the first six to seven months, fermentation converts the sugars into alcohol, taste and aroma components. After the fermentation process, it is time for the beer to mature for at least six additional months and develop its characteristic taste. In some cases, the beer will mature in the foeders for several years.


As lambic undergoes several months or even years of fermentation and maturation, a lambic brewery must have enough storage space. Lindemans for instance always has more than six million liters of beer fermenting and maturing, which is the equivalent of 24 million glasses of beer.

Let’s have a closer look at two of their beers.

Oude Gueuze Cuvée René has a golden colour and beautiful sherry aromas. This old gueuze is a blend of old and young lambic that has matured in the foeders. Young lambic still contains enough yeast and sugars to continue to ferment in the beautiful champagne bottle, so a second fermentation takes place. This process produces carbon dioxide, resulting in a slightly carbonated beer with a nice foam. When kept in a cellar for a few years, the Cuvée René becomes truly exceptional!

The Old Kriek Cuvée René does not require any blending. The cherries are ferment for six months in a lambic that is at least six months old. Afterwards the Old Kriek is directly bottled for a second fermentation process. The result is a beer with a pure cherry flavor and a wonderful sour-sweet balance making it a perfect aperitif.


All picture credits: (c) Lindemans