Fermenting your beer is the last step in the homebrew process and it requires a little bit of care to do properly. The yeast essentially turns the sugars in your wort into alcohol, and finally you have beer.
Fortunately, it is a relatively simple process that mostly takes care of itself after the initial procedure. It might be up to two weeks before you can drink your beer so a little patience will go a long way in making sure that you don’t mess up an otherwise smooth brew day.
How the Beer Fermentation Process Works
Once the yeast is mixed into the cooled wort, it begins to consume nutrients and oxygen and multiplies. The yeast continues to multiply until all the oxygen in the wort is consumed.
Next, the yeast begins to consume simple sugars. This part of the fermentation is vigorous and produces CO2. You will also see a foamy head on top of the wort surface, sometimes rising by up to one foot.
As the fermentation process continues, CO2, alcohol, and congeners are produced.
Finally, the yeast consumes all the simple sugars and begins to become dormant and the process begins to slow down. Some of the yeast, however, remains active and attacks the complex sugars and additional byproducts in the beer.
Eventually, the yeast consumes everything it can, becomes dormant, and falls to the bottom of the fermenter.
The yeast incessantly feeding produces alcohol.
Requirements for Fermentation
Most of what you need for the yeast to work is already in the wort. These requirements include sugars, lipids (fatty chemicals), amino acids, and minerals.
Oxygen, although something that you have been avoiding up until this point of the brewing process, is a necessary requirement for fermentation. Oxygen in the wort allows the yeast to produce sterols, which in turn causes the yeast to multiply and grow.
Yeast that doesn’t grow or multiply sufficiently during the fermentation process leads to beer that isn’t full fermented, also known as under-attenuated beer.
You can add oxygen to your wort by pouring it vigorously from a height into your fermentation carboy or bucket, allowing the wort to slosh and mix around. You may transfer the wort back and forth a few times in this manner for good measure.
Fermenting Ale vs. Lager
The fermentation process for ale is a little different from that of lager. In fact, one factor that differentiates ales from lagers is the specific fermentation method used for the particular beer.
The type of yeast used for fermenting ale is known as Saccharomyces cerevisiae, which is also the kind of yeast you see in wine and bread making. This kind of yeast quickens the fermentation process and ale can be ready to drink in a week’s time.
The optimum fermentation temperature range for ale is between 60°F and 80°F. Most types of yeast die if the temperature goes above 104°F.
The yeast used in fermenting lagers can withstand high alcohol concentration which is why ales typically have higher alcohol content than lagers.
Ale goes through a fermenting process known as top-fermentation which simply means that the yeast is poured directly on top of the wort and starts to work from the top-down.
Generally speaking, top-fermented beer has stronger flavors.
The yeast typically used in fermenting lager is known as Saccharomyces uvarum. The optimum temperature range for fermenting lager is between 45°F and 55°F.
Lager is referred to as bottom-fermented beer which means that the yeast in the wort begins to work from the bottom-up.
Lager yeast dies off when the alcohol content rises beyond a certain point which is why lager generally has lower alcohol content than ale.
The fermentation process is also much slower than that of ale and results in a clearer and crispier beer.
How to Ferment Beer Step-by-Step
What You Need:
- Primary fermentation vessel
- Airlock or blow-off assembly
- Secondary fermentation vessel (optional)
1. Sanitize Your Equipment
Once the wort temperature comes down, your beer is open to infection. Sanitize all the equipment you will use for the fermentation process including your airlock/blow-off assembly, hydrometer, fermentation vessel, hose, scissors, yeast packet, and anything else that will come into contact with your wort.
2. Transfer the Wort to the Fermentation Vessel
Once the wort is at the ideal pitching temperature, transfer the liquid to your fermentation vessel. Pour vigorously to get some air into the wort. Top off the wort with water, preferably drinking water, to make up for the volume lost due to evaporation while boiling the wort.
You can also rock the fermentation vessel back and forth for a few minutes with the lid on to introduce oxygen into the wort.
3. Check the Original Gravity
Take a sample of the wort and check its original gravity. Note down the number since you will need it later. You need the original gravity along with the final gravity to determine the beer’s alcohol by volume (ABV).
4. Pitch the Yeast
Pitching the yeast simply means adding the yeast to your wort. Pour in the yeast on top of the wort or follow the directions on the yeast packet.
5. Seal the Fermentation Vessel
Seal the fermentation vessel tight and attach the airlock and stopper. Fill the airlock with clean drinking water or sanitizer to the appropriate marking.
Place the fermentation vessel in a dark room with a stable temperature. Make sure that the location is easy to clean since a violent or vigorous fermentation process can create a mess.
Check-in after 24-48 hours and you should see the liquid in the airlock bubbling. This bubbling means that the CO2 from the fermentation is escaping the vessel and that fermentation is happening.
Wait for a week or two depending on the type of beer for the process to complete.
7. Bottle/Keg Your Beer
You should notice that the bubbling in your airlock has greatly reduced or stopped completely once your beer is done fermenting. Depending on the type of beer, this should be within a week or two of pitching the yeast.
Transfer the beer into a bottling bucket and add any bottling additives that may be included in your recipe such as priming sugar.
Take your beer’s final gravity to determine the approximate ABV of the final brew.
Bottle or keg your beer using the appropriate procedure.
Most people new to all-grain brewing typically don’t have to worry about secondary fermentation but it’s still worth exploring it in this guide.
Secondary fermentation simply involves transferring your fermented beer to a secondary fermentation vessel, usually a glass carboy. The beer sits in the secondary vessel for anywhere from two days to several months. This is typically the stage where homebrewers will dry hop beer.
Secondary fermentation leads to a clearer beer and results in less sediment at the bottom of the bottle or keg. Secondary fermentation also often results in a smoother and better-tasting brew. Lagers may take up to a month in secondary fermentation.
Ale yeast, on the other hand, requires less time in secondary fermentation since this type of yeast cannot process more complex sugars as is the case with lager yeast. Secondary fermentation may take about a week for ale.
Downsides of Secondary Fermentation
Before you decide that secondary fermentation is for you, there are some downsides to including this step to your brewing process.
The first downside is the cost. Secondary fermentation typically takes place in glass carboys which are more airtight than fermentation buckets. This means that you need more equipment, bringing up the cost of operating your home brewery.
Secondary fermentation also brings with it the inherent risk of infecting your beer. There is also the risk of introducing oxygen into your beer, which could lead to stale flavors and other undesirable flavors.
It may be worth sticking with primary fermentation for the meantime until you are ready to experiment with your brewing process.