Although yeast is one of the simplest forms of plant life, this amazing microorganism is responsible for carrying out the fermentation process in beer making.
An ancient but invisible ingredient
Yeast wasn’t even considered an ingredient in beer until its role in fermentation was discovered and understood. This innovation began with the creation of the microscope in the early 1700s and was advanced by Louis Pasteur nearly a century later. Ale yeast has an ancestry that reaches into ancient times. The lager yeast variety was perfected only in the mid-1800s. Before this discovery, brewers couldn’t make what’s now called a lager. They had to brew ale, ferment and store it at cold temperatures, and hope for the best.
In 1842, when combined with the Czech Republic’s local Saaz hops and the newest developments in pale malt, yeast helped to create what is credited as the world’s first clear, golden lager.
While in Africa, the Khoisan used ‘honey wine’, which is honey and water, fermented with yeast found naturally in the honey. The drink, called ‘!karri’, was used in many of their religious practices.
Yeast In The Brewing Process
It wasn’t until the late 19th Century that yeast was properly understood, but today it is a vital element that imparts flavours exclusive to a specific brewery. Without yeast, beer would not contain alcohol.
Yeast essentially feeds off the sugars of the malty wort, the liquid extracted from the mashing process during the brewing, and produces two things that are essential to a great beer. Firstly, carbon dioxide, and secondly, alcohol. Many brewers consider their yeast to be a secret ingredient and often fiercely guard the identity of the strain.
The majority of beer contains between 4 and 6 percent alcohol by volume although many higher volume styles are produced. After reaching a level of 8 or 10 percent fermentation is effectively over. To achieve higher alcohol levels a more robust champagne yeast can be used.
How Yeast Affects Beer
Yeast can also take credit for the classification of the beer style, as all beers are either a form of ale or lager. Ale yeast, which is a top-fermenting strain, works best in warm temperatures, e.g. 15°C to 24°C. Lager yeast, which is a bottom-fermenting strain, performs best in cooler temperatures, e.g. 3 to 11 degrees Celsius. Because of the temperature difference, each yeast strain produces diverse flavour and aroma characteristics that, in turn, create the different beer styles.
Yeast, in combination with different fermentation processes, can also contribute additional flavour characteristics such as notes of banana, fruitiness and bubble gum. There are hundreds of yeast strains available around the world, each imparting a somewhat different flavour. As well as enjoyable flavours, many off-flavours in beer are also result of yeast issues!
Ales normally comprise more robust-tasting beers, and tend to be fruity and aromatic. They include bitter beers with a distinct, complex taste and aroma, and are enjoyed warmer at between 7 to 12 degrees Celsius. These include our recently launched No 3 Fransen Street’s Irish Red and Cream Ales.
Lagers usually include lighter-tasting beers, and tend to be extremely bubbly or crisp. They usually are fresh, balanced in taste and aroma, and are served fairly cool between 3 and 7 degrees Celsius. Some of our lagers include Castle Lager, Hansa Pilsener, Pilsner Urquell, Peroni Nastro Azzurro and Grolsch Premium Lager.
Whether you prefer ales or lagers, don’t forget that all important ingredient which gives your favourite brew its unique taste.