Spontaneous fermentation refermented in the bottle
At a certain moment in the brewing process, the wort must be cooled into shallow cooling vessels. The brewer throws open vented windows, turns on fans and leaves the liquid overnight to cool. The brew then has maximum contact with the surrounding air so the wild yeasts and other microbial flora can graft on the wort. The spontaneous fermentation can start. The sugars present in the wort can now be turned into alcohol and carbon dioxide. This fermentation of wort only takes place in a small area around Brussels and only from October until April, when outside temperatures remain under 15°C.
Refermentation of beer
A small amount of pure yeast culture is added to the beer just before bottling. The yeast can now turn the remaining sugars into alcohol and carbon dioxide. Sometimes liquid sugar is added to feed the yeast. After that the beer can referment in warm chambers for several weeks. The refermentation proceeds in the bottle and gives the beer a more delicate aroma and a typical taste. The beer evolves and will become more complex. During the maturation process, the yeast falls to the bottom of the bottle. So when you come to pour it, you can either pour out the yeast into your glass or leave it in the bottle depending on your preference.