Without yeast, beer is nothing. And yet, brewing yeast remains the single most underappreciated beer ingredient, maybe because it was discovered last of all the ingredients or because it looks fairly unattractive. Despite all of this, the single-celled microorganism deserves our respect. This is because it has a huge impact on the beer flavor, as well as the brewing process. Water, malt and hops would be a weirdly tasting cluster of ingredients if this secret agent never existed. In short, yeast ignites the fermentation process and helps make the beer what it is, the most wonderful drink in the world.
So how does yeast do its magical work? When pitched, the yeast wants the sugars in the cooled beer wort (unfermented beer full of sugars released by the malt during the mashing process) because its natural instinct is to reproduce. A single-celled organism, one yeast cell is divided into approximately five new ones during this process. What the brewers are interested in is not the wellbeing of the yeast family, but the byproducts of this reproduction - the CO2 and alcohol. As yeast grows, it also produces around 500 metabolic compounds that affect the beer flavor, i.e. fruity or clove aromas. As we can see, yeast is a hard and diligent worker. The quantity of yeast used for brewing depends on the type of beer brewed, but we are talking about billions of yeast cells even for a small batch.
The beer family tree is divided by the type of yeast used. The upper fermenting ale yeast favors warmer fermentation temperatures, typically between 10 and 25°C, while the bottom fermenting lager yeast prefers colder ones in the 7 to 15°C range.
Some brewers, traditionally in Belgium, love to leave their beer in the open to the mercy of wild yeast and various microbes in a process called spontaneous fermentation. However, most brewers prefer their results to be more or less consistent so each brewery grows its own yeast strain.
Brewing is indeed all about orchestrating ingredients and the brewing process to make a fine tasting drink for the world to enjoy. And yeast plays a huge part in it. Isn't brewing yeast the best microorganism out there?
