What Is Beer Yeast?
Beer yeast is a fungus that grows with or without oxygen and reproduces by budding (asexual splitting). The brewing process includes yeast that uses glucose and maltose and converts them into ethyl alcohol and carbon dioxide during fermentation. In addition to these, you will get by-products, such as:
Esters –
These molecular compounds add recognizable fruity notes to the beer.
Phenols –
They are responsible for spicy and medicinal notes when combined with chlorine.
Diacetyl –
This ketone compound gives beer a butter note, desired in Stouts, Pale Ales, and Scotch Ales. Be careful since it is quite unstable and takes on raunchy tones over time.
Fatty acids –
They produce off-flavors in old beers as a result of the oxidation process.
Fusel alcohols –
These alcohols with heavy molecular weight are responsible for sharp beer notes. They also cause unpleasant hangovers after drinking too much beer.
Yeast Types
Brewing recognizes two primary beer yeast types that differ in characteristics, the temperature of growing, and the way they work.
Which yeast strain you need will depend on the type of beer you choose to produce. For example, you will get an entirely different beer when using ale or lager yeast, even if all the other ingredients are the same.
Top-fermenting yeast is necessary during fermentation that takes place at the top of the fermenter. On the other hand, bottom-fermenting lager yeast will sink to the bottom during fermentation.
The crucial difference in using these two yeast strains is the brewing temperature. While ale yeast works at warmer temperatures above 55°F (13°C), lager yeast prefers working in a range of 50 to 55°F (10 – 13°C). An exception is lager yeast that requires ale temperatures of 60 to 70°F (15.5 – 21°C) and helps to produce California Common Beer.
If you enjoy home-brewing, you should experiment with various available yeasts until you find the perfect combination that suits you best.
1. Ale Yeast
Top-fermenting ale yeast is crucial for ales, stouts, porters, Kölsch, Altbier, and wheat beers. It rises to the surface of the container during the fermentation process.
Ale Yeast History
Ale brewing is the oldest method of beer production, dating back to ancient Egyptian times. You can use any of numerous ale yeast strains that ferment quickly, even in anaerobic fermentation conditions.
Their advantages include the ability to use a desired sugar profile and tolerate moderate alcohol levels. As a result, ale yeast provides a unique beer taste because its natural mutation prevents phenolic off-flavor production.
You can choose from many varieties of ale yeast strains, each with different flocculation, attenuation, and flavor profiles. You can experiment and finally choose the one you like the most.
Fermentation Process
Regardless of the differences between the strains, these yeasts have something in common. The ideal fermentation temperature for all strains is 68°F (20°C), but they can tolerate temperatures up to 95°F (35°C). Keep in mind that the beer will taste best at the ideal temperature, and any change will significantly affect the final flavor.
All ale yeasts rise to the top of the fermenter during the fermentation process and create a thick yeast head. Most strains will reach the surface after 12 hours of fermentation and continue to ferment there for an additional 3 to 4 days.
You can collect the yeast from the top during the cropping phase and use it later for new production. The pitching rate for ale yeast is 5 to 10 million cells per milliliter.
Ale yeast that produces fruity beer is usually less versatile but attractive for most brewers. This strain ferments at the same temperature but flocculates quickly and creates different flavor compounds, known as ‘clean fermenters.’ Yeasts that produce more fusel alcohols and esters are considered fruitier.
2. Lager Yeast
Bottom-fermenting lager yeast is necessary for Märzen, Pilsners, Bocks, Dortmunders, and American malt liquors production. It settles to the bottom of the container at the end of fermentation.
In some cases, brewers who prefer bottom-fermentation use a hybrid of Saccharomyces cerevisiae and wild strain yeast from Patagonia to get alternative lager beers.
The advantage of lager yeast is the ability to thrive at low temperatures. As a result, the fermentation process takes longer, and the beer is crisper with fewer pronounced ale flavors.
The third option is the use of wild Brettanomyces strain, which provides a decidedly funky flavored beer profile. Many American craft brewers experiment with wild fermentation but in a controlled setting.
Lager Yeast History
Most brewers use Saccharomyces uvarum isolated at the Carlsberg Laboratories in 1881. Emil Christian Hansen developed the first techniques for growing pure lager yeast cultures.
That pure form created a semi-hard surface when combined with wort and agar and could stay alive for a long time. The long-term storage allowed this product to be transported worldwide, making a new beer type with a long shelf life popular.
Fermentation Process
As mentioned earlier, lager yeast ferments best at 50 to 55°F (10 – 13°C). Cold fermentation results in fewer fusel alcohols and esters. However, the sulfur residue level in the solution is higher, making it more difficult for the yeast to absorb diacetyl.
This can be solved by raising the fermentation temperature when the beer reaches a specific gravity of 1.022 to 1.020. Increase the temperature to 68°F (20°C).
When the specific gravity drops to approximately 1.010 to 1.014, let the product sit for 3 to 5 days at the same temperature. Then cool it to 50°F (10°C) for one day before lowering the temperature to the desired range of 41 to 45°F (5 – 7°C).
Remember that the optimal lager pitching rate is almost twice that of ale yeast, so you need approximately 15 to 20 million yeast cells per milliliter for excellent-tasting beer.
3. Belgian Yeast Strains
Most Belgian brewers use unique yeast strains to make their famous beers. Since they use numerous strains, it is almost impossible to determine the particular one for each beer type.
In general, you can make Belgian wit beer with traditional lager yeast, but it won’t have the unique taste of a Belgian beer fermented with an authentic yeast strain that provides clove, phenol, ester, earthy, and fusel alcohol flavors.
To produce Belgian-style beers, you need to be creative, achieve the desired balance of compounds, and have the right recipe. Unfortunately, all your preparations and high-quality ingredients mean nothing without the particular yeast strain that determines the flavor profile of the beer.
4. Wheat Beer Yeast
To get a traditional European wheat beer with a recognizable flavor, you will need specific wild yeast strains. These strains are necessary when you want to brew a beer with a pleasing taste.
Nowadays, you can find only half a dozen wheat beer yeast strains that slightly differ in flavor. Most wheat beers have the traditional cloudiness because of the strains used, which do not flocculate well. This characteristic is their primary advantage.
Summary
Nowadays, many people enjoy making homemade beer. Most of them experiment with different yeast strains to get unique flavors and desired alcohol content.
If you are one of them, you need to understand brewing yeast biology before starting production. Only then can you fully enjoy your favorite beverage. Cheers!
