Flocculation refers to a yeast strain’s tendency to clump together and drop out or fall out of suspension to the bottom of the fermenter or holding vessel. As yeast flocculates, the beer begins to clarify. Some yeast strains tend to have high flocculation, such as Wyeast Scottish – 1728, while other strains like Wyeast American Wheat – 1010 have very low flocculation. The physical appearance of the yeast cell plays a big part in its flocculation level.
It is important to choose a yeast with an appropriate flocculation profile when designing a beer; for instance you would not pair a Belgian Wit wort with a high flocculation yeast, as you want some of the yeast to stay in suspension in the finished beer.
An airlock or fermentation lock is a single direction sanitary valve used during fermentation. It allows the large quantities of carbon dioxide being produced by the yeast to escape while not permitting outside air\oxygen or contaminants to enter the fermentation chamber. This creates a sanitary seal on the fermenter and helps prevent the oxidization of the fermenting beer.
The airlock or fermentation lock typically contains a sanitizer to help maintain the integrity of the fermenter. Airlocks tend to be made of clear plastic or glass so that the CO2 bubbles passing through them can be monitored as a way of gauging how active the fermentation process is.
Below is an example of a three piece airlock, S shaped airlock, and a blowoff tube.
Example of different types of airlocks/fermentation locks and a blowoff tube.
Brett or brettanomyces is a high attenuation yeast strain that is known for the acidic, funky, wild\barnyard type tastes and smells that it produces. In most beer styles, brett it is perceived as an unwanted contaminant due to its strong and distinct flavors that can overwhelm more subtle beer flavors. Yet it is highly prized in some Belgian ales, such as gueuze, lambics, farmhouse ales, and Flanders red ales.
It is even used in one of my favorite Belgian Trappist beers called Orval, where their brewers add it at bottling, and allow it to ferment out and condition over time. Brettanomyces has grown in popularity over the last several years and is now used in a wide variety of styles and by many US craft breweries. When brewing with brett, it is important to avoid cross contamination with your non-brett beers as it is a robust yeast strain that can easily modify a beer’s flavor and aroma.
The most commonly used brett yeast strains are White Labs WLP644 Brettanomyces Bruxellensis Trois, White Labs WLP645 Brettanomyces Clausenii, White Labs WLP650 Brettanomyces Bruxellensis and Wyeast 5526 Brettanomyces Lambicus.
Bottom fermentation or bottom fermenting is a term that describes the manner in which lager yeast tends to collect on the bottom of the fermenter and conducts its fermentation, as opposed to top fermenting ale yeast, which conducts most of its fermentation on the top of the beer. Bottom fermenting lager yeast strains prefer a low fermentation temperature range that is typically between 40° F and 55° F, but varies between strains.
Autolysis is the destruction of a cell by the actions of its own enzymes. In brewing, autolysis typically occurs when yeast cells either decay over time or destroy each other. When the outer wall of the yeast cell is degraded and can no longer contain itself, it releases off flavors and odors into the beer. These odors are typically described as rubbery in aroma.
Autolysis is most common in aged beers, but can also occur in a fresh beer due to a variety of factors including unhealthy\aged yeast, stress caused by too rapid of a fermentation, excessive temperature changes and high alcohol levels. One of the best ways to reduce the impact of autolysis is to conduct a secondary fermentation as a means of removing the beer from the yeast cake. Other ways of reducing the impact of autolysis is proper aeration of the wort prior to fermentation, avoiding oxidization, keeping a consistent and appropriate fermentation temperature, and properly regulating the temperature of your finished beer.
Apparent attenuation is the measurement of the percentage of sugars that have been converted to alcohol by the yeast in a beer. Apparent attenuation is equal to the original gravity minus the final gravity divided by the original gravity, showing the percentage of conversion. A typical apparent attenuation range is between 65 and 80%.
Apparent attenuation calculation example:
Original Gravity of sample beer = 1.06
Final Gravity of sample beer = 1.012
Calculation: 1.06 – 1.012 = .048
.048 / .06 = 80% Apparent Attenuation
There are a variety of ways to impact your apparent attenuation. Some of these include the type of yeast you use, the amount of yeast you pitch, your mash temperature(s), your grain bill composition, and your mash PH. If you are doing extract brewing, then the primary impacts will come from your yeast and any unfermentable sugars that you may add, such as maltodextrin.
An ale is a beer that has been fermented using a top fermenting yeast. Ale yeasts are typically more resilient to warmer temperatures then their lager counterparts and are usually fermented at a temperature range of 65-75 F. Since the yeast is more active at higher temperatures, an ale ferments much quicker then a lager.
Examples of ales include golden ales, pale ales, India pale ale, old ale, Belgian ale and barley wines.
Something to keep in mind when fermenting an ale is that ale yeast can ferment beer above a temperature of 75 F, but when doing so it will oftentimes create undesirable esters and off flavors. Also, liquid ale yeast is vulnerable to high temperature, and it should be refrigerated to maintain its viability in transit and in storage. Due to the delicate nature of liquid yeast, I always create a yeast starter to verify its viability prior to pitching it in the cooled wort.