The clear wort which leaves the filter-press is led to a boiling vessel where it boils for one hour.

This is the moment that the hops are added. Part is added at the start of boiling, and the remainder at the end in order that the bitterness and aroma are well established in the beer.

The boiling sterilises the wort. This allowed the patron saint of brewers, Saint Arnould, to work a "miracle". At the time of the plague in Flanders (in the XIth century) those who wished to avoid the terrible plague were advised to drink beer.

Those who listened were saved. But this was no miracle it was the boiling that sterilised the water. In fact, boiling their water before drinking it would have been sufficient... but this would destroy the legend!