Home Brewing Blog

Beer Yeast

What is Yeast?
Yeast is very small, single cell organisms. Yeast are everywhere, on plants, in soil, and in the home. One species of yeast, Saccharomyces cerevisiae, has been "domesticated" over the centuries to produce good beer. Now there are hundreds of different strains of Saccharomyces cerevisiae available to make beer.

What Makes Liquid Yeast Different?
Liquid yeast has many advantages over dried yeast. The variety of liquid strains is much greater, but most important is the flavor profile. Most brewers would agree that beer made with liquid yeast is superior in flavor, and consistently wins medals over dried yeast in national competitions. Most liquid yeast on the market is supplied in small quantities.

How is Yeast Used?
Once wort is transferred into the fermentor, shake the fermentor vigorously to get plenty of oxygen into solution. This will help fermentation, and is the only time oxygen should be introduced into the brewing process. Brewers call adding the yeast "pitching". Before pitching, make sure the wort temperature is between 70-80 °F. Too cold and the yeast will take too long to begin fermentation, too hot and the yeast can be killed.

What Should the Fermentation Profile Look Like?
Normal fermentation will begin 5-15 hours after pitching the yeast. During this "lag phase", yeast becomes acclimated to their environment and uptake sugars and oxygen they will need for the fermentation. The first sign of fermentation activity will be a raised airlock. This signals <?xml:namespace prefix = st1 />CO2 production. A fine layer of foam will then form on top of the liquid. Within a few hours the head will get rocky and the airlock will quickly expel CO2. Fermentation will usually be complete in 5-20 days. If there is not enough room for foam, the foam may get into the airlock and then blow the airlock off the container! So be careful and allow plenty of headspace, or use a blowoff tube for the first 3 days. The airlock will bubble very slowly, and the yeast will begin to drop to the bottom of the fermentor. Check the gravity, if fermentation is complete and yeast is still on top of the beer, either cool the fermentor to force the yeast down or transfer the beer into a different container.

Types of Yeast (Ale, Lager, Lambic & Belgian)

 Warm fermenting (Ale)

Ale Yeast are generally fermented at warm temperatures between (65–68 °F), occasionally as high as 75 °F They generally form a foam on the surface of the fermenting beer, as during the fermentation process its hydrophobic surface causes the flocs to adhere to CO2 and rise; because of this they are often referred to as "top cropping" or "top fermenting".  Warm fermented beers are generally ready to drink within three weeks after the beginning of fermentation, although some brewers will condition them for several months.

Cool fermenting (Lager)

Lager is beer that has been cool fermented, at around 55 °F, compared to typical warm fermentation temperatures. It is then stored for 30 days or longer close to the freezing point, and during this storage sulfur components developed during fermentation dissipate.

Though it is the cool fermenting that defines lager, the main technical difference with lager yeast is its ability to process raffinose (composed of the sugars galactose, fructose, and glucose) which means that all sugars are fermented, resulting in a well attentuated beer; top-fermenting yeast only ferments the fructose portion of raffinose.

Today, lagers represent the vast majority of beers produced, the most famous being a light lager called Pilsner  Lagers range from very light to deep black.

Lager yeast for 2nd stage ferment at a temperature of approximately (40 °F). Lager yeast can be fermented at a higher temperature normally used for top-fermenting yeast, and this application is often used in a beer style known as "steam beer".  I typically ferment at 53-58 °F for three to four weeks and then lager it at  35-38 °F for a minimum of two weeks.  Then you can lager longer or bottle and let it lager in the bottle a couple/few weeks.

Spontaneous fermentation (Lambic)

These beers are primarily brewed around Brussels, Belgium. They are fermented in oak barrels after being inoculated with wild yeast and bacteria. Wild yeast and bacteria ferment the wort (unfermented beer) in the oak barrels. The beers fermented from yeast and bacteria in the Brussels area are called Lambic beers. These bacteria add a sour flavor to the beer. Of the many styles of beer very few use bacteria, most are fermented with yeast alone and bacterial contamination is avoided.

Middle fermentation (Belgian)

Belgian yeast is very distinctive, unlike the two other major components of beer which are fairly standard but applied in unusual ways. Trappist ale yeasts create what could be considered a very high level of esters, iso-amyl acetate (associated with the taste and aroma of bananas) in particular. The same could be said of many Specials whose flavor profiles mimic that of a Tripel. Lactic acid production is another very unusual aspect of Belgian yeast activity. The resulting sourness can be found in a wide range of brews. Lambics, some Brown ale, some Red ale, and some Specials can be examples of this.