Having examined the role of principle raw materials used in the brewing process, we have essentially reached the most important piece in the creation of beer. That being the fermentation of sugars by yeast. The chemistry of water, sugars and nutrients present in malted grain and the oil contained in hops all play a crucial role in the making of a sweet grainy liquid called wort, but it is not until we introduce yeast that we truly see the transformation into beer.
Yeast is a single cell fungus that is present all over the natural world. Having developed over millions of years, this tiny creature has adapted to consume sugars and through an incredible biochemical process, it converts them into alcohol and carbon dioxide. For centuries people have relied on yeast for making their nourishing bread and beer, not truly knowing what was causing this fermentation process. It wasn’t until advancements in microbiology in the 19th century and the invention of the microscope did humans begin to grasp the importance of this incredible creature.
For brewers, there are new main families of yeast that are employed to ferment their wort. Saccharomyces Cerevisiae and Saccharomyces Pastorianus, commonly known as ale yeast and lager yeast. Ale yeast ferments at room temperature, on the surface of the wort and in a relatively quick fashion. Lager yeast likes to ferment at a cooler temperature and at the bottom of the fermentation vessel, which takes a bit more time.
The warmer fermenting ale yeast can create a range of flavours and aromas in beer. From the banana and clovey aromas of German wheat beers to big tropical fruit esters created by some English ales strains, and spicey phenolics from Belgian ale strains. Brewers carefully select from dozens of yeast strains to create a finished beer that expresses the attributes they desire.
The cooler fermenting lager strains produce a cleaner, crisper beer. These yeast strains have developed to create a refreshing beer that has grown in popularity from its initial discovery in the 19th century to become the most commonly consumed beer on the plant, and most like the first taste of beer you had coming of age.
Brewers carefully formulate their recipes for wort to create a finished beer that meets the characteristics they want in the finished glass of beer that comes across the bar or in the can, but in order for this to occur they need to carefully tend to yeast, as this little creature is truly responsible for that refreshing pint you drink.