In our latest Beer Ingredients blog post, we’ll be looking at the importance of yeast in the brewing process. This key ingredient kick-starts fermentation and contributes to the flavour and aroma of the resulting brew. Put simply, without yeast there would be no beer! What is it? Otherwise known as Phylum Ascomycetes, yeast is a single-celled organism, commonly used in brewing for its fermentation of carbohydrates into carbon dioxide or alcohol. This useful fungi comes in two varieties, namely top-fermenting yeast (Saccharomyces Cerevisiae) used for ales and stouts, and bottom fermenting yeast (Saccharomyces Uvarum) used for lager. How is it added? At the final stage of the brewing process, yeast is added to the wort - the sugary liquid extracted from mashed grains and water. Once added, the wort is transformed into beer through the fermentation of sugar into carbon dioxide and alcohol. Top-fermenting yeast produces foam on the surface of the beer unlike bottom-fermenting yeast, which simply gathers at the bottom of the brewing vessel. What does it do? The main function of yeast is to initiate the fermentation process, reacting with the sugary bi-product of malt to create alcohol. It is the final component of the brewing process that determines the flavour and aroma of the beer. Yeast and St. Stefanus At St. Stefanus, yeast is added regularly throughout the brewing process to keep the fermentation of our beer fresh and vigorous. We use three different kinds of yeast, including the original Jerumanus yeast strain from the Sint Stefanus Monastery, which imparts our beer with its distinctive flavour and aroma. The brewing process of our abbey beer is equally special - unlike most high fermentation ales, our beer is not pasteurised right after fermentation. Instead, some of the yeast is removed from the beer, which is then stored for four weeks at for its first stage of maturation. After this month, the remaining yeast is filtered out and the temperature raised to create the optimal environment for the addition of two secondary yeasts. These two yeasts are added as the beer is bottled, along with a little hot water and sugar that causes the beer to foam, ridding the bottle of any unwanted oxygen. The bottles are then stored at a warm temperature for two weeks, as the secondary fermentation gets under way. Once removed from this “refermentation room”, the bottles are stored at cellar temperature for three months, allowing our distinctive flavour to develop. Watch our video below to find out more about the St. Stefanus brewing process.