May 15, 2020


Cold Crashing Beer

What Is Fermentation?

When the brew day is over and the equipment has been cleaned, it is time to allow the yeast to ferment your beer. Your beer will ferment best in a warm place (check your yeast strain for its preferred fermentation range), out of sunlight, and not easily disturbed.

Fermentation is the scientific process of yeast, a single-celled organism, consuming sugars from various sources like malted barley, and converting them into Co2 and alcohol. The study of fermentation is called Zymology or Zymurgy, a term you may have already seen in your brewing research. Louis Pasteur, the man behind pasteurizing is also the scientist who discovered yeast and was the first zymurgist. You can read all about yeast in our article, What is Beer Brewing Yeast?

Fermentation is found in more than just beer. Within the walls of Northern Brewer, you can get supplies to make wine, cider and mead, and kombucha. And by no means is fermentation even limited to the above products, and there’s a plethora of information out there if you choose to do the research.

We’re mostly here for the fermentation of the almighty beer. When fermenting beer, there are usually two stages to fermentation, primary fermentation and secondary fermentation. As you get more advanced you might find you only need a primary fermentation or you might even add in a third fermentation called tertiary fermentation. The possibilities are limitless.

Fermentation is not a “set it and forget it” process (though it can be!). Through centuries of study and beer making, we’ve been able to dial in the fermentation to produce the best possible results for our beer. A few factors to consider for successful fermentation are temperature, yeast type, an air-tight seal, and light. We’ll discuss each of these below.

Primary and Secondary Fermentation

Primary Fermentation

As the name suggests, primary fermentation is the first stage of your beer’s fermentation journey. Once the initial boil is complete and your wort is chilled to the optimal temperature range, transferred to the fermentation vessel, and yeast pitched, primary fermentation will begin.

Once the yeast is pitched, the hungry little organisms will begin devouring the sugars contained in your wort. It’s during primary fermentation where your wort actually becomes beer. Fun fact, legally wort becomes beer the moment yeast is added to it, so no minors past this point…. You should start to observe signs of fermentation within  48 hours of pitching your yeast. If you plan to add any yeast nutrients, you’ll want to add those to the primary fermentation.

Although CO2 bubbles escaping through the airlock is the most obvious sign of fermentation, it is not an absolute or even the best indicator. Some fermenters may not be 100% airtight, which will allow the CO2 produced to escape without going through the airlock. If you do not observe any bubbles after the first 48 hours, you can verify that the fermentation is occurring by opening the lid slightly and looking for a foam layer (called krausen) on top of the beer or a ring of sludge around the fermenter indicating that krausen was once present and has already subsided.

Secondary Fermentation

Secondary fermentation is a period of aging that occurs after primary fermentation is complete. The fermented beer is siphoned (also called racked or transferred) from the primary fermenter to a secondary fermentation vessel. Contrary to its name there is actually very little to no yeast activity, or fermentation, occurring during secondary fermentation, because of this it is also referred to as the conditioning phase. Transferring your beer to secondary will allow the beer’s flavors and aromas to mellow and blend together. We often compare this process to the way a batch of chili tends to taste better after a day or two in the fridge and all of the flavors have had a chance to blend together. Additionally, a secondary fermentation allows time for the yeast to drop out of solution, producing a clearer finished product.

For many beers with an original gravity of 1.040 or lower, or beers that are usually served cloudy, secondary fermentation is usually not necessary. It is almost always used for higher gravity and highly hopped beers that need time to age before reaching their peak flavor and aroma. You will also need to employ a secondary fermentation when adding dry hops or oak chips.

The duration of a secondary fermentation or conditioning phase can vary from as little as a week to over 6 months. Actual time will vary and you should let your taste buds, and nose, determine when a beer is ready for bottling. During extended secondaries, you should make sure your <airlock does not dry out. For this reason, a bubbler airlock is best for secondary fermentations because they allow you to easily monitor the liquid level and prevent it from drying out.

Top and Bottom Fermentation

Most brewing yeasts like to ferment at temperatures between 55-75 F, but each yeast will prefer a slightly different temperature range. In most cases, ale yeast will work best between 65-75 F. If the temperature is too cold, the fermentation will proceed very slowly or the yeast will actually start to hibernate. If the temperature is too warm, it is possible to develop undesirable off-flavors or even kill the yeast before they finish fermentation.

Brewing yeast generally falls into two categories and each prefers its own temperature range.

  1. Top Fermenting Yeast (Ale Yeast)
  2. Bottom Fermenting Yeast (Lager Yeast)

Top-Fermenting Yeast

Top-fermenting yeast, also known as ale yeast needs to ferment at warmer temperatures, 50-77 degrees Fahrenheit. It’s called top-fermenting because the yeast rises to the top of the fermenter during fermentation. The yeast cells float on the top of the fermenter because they actually hitch a ride with Co2 molecules as they rise to the top of the fermenter. Top-fermented beer often ferments in just a few days. The beer which results from top-fermenting yeast is called ale. There are many different styles of Ale, too many to list them all here, but some common examples include pale ales, stouts, and wheat beers.

Bottom-Fermenting Yeast

Bottom-fermenting yeast or lager yeast needs to ferment at cooler temperatures, 41-50 degrees Fahrenheit. It’s called bottom-fermenting because the yeast drops to the bottom of the fermenter once they have finished fermenting the sugars of the wort. The colder temperatures tend to mean the yeast work slower, and therefore extend the time of primary fermentation. Lager yeast can often take 10-14 days to complete primary fermentation. Lagering is the term used to describe bottom fermentation, and as a result, it is also the name of the resulting beer style. Lager-style beers include pilsners like the ‘Czech Pilsner’, bocks like the ‘Maypole Maibock’, Dortmunders, malt liquors, as well as various regional lager styles from all over the world like the ‘Atlantico Mexican Lager’.

Avoiding Off Flavors During Fermentation

Regardless of the type of yeast, you’re using, you’ll want to ensure other factors are in place for optimal fermentation. Most notably the location where you ferment your beer is important. Sunlight can negatively affect the flavor of your beer by modifying the hops flavor and aroma. This flavor and aroma have been described as skunky, which is obviously not very desirable. This is actually the reason why most beer bottles are brown! Long story short your fermenter should be out of direct sunlight and covered if it is clear.

Like sunlight, oxygen can also have a negative effect on your beer. You’ll also want to make sure your fermenter has an airtight seal. Airlocks (or Fermentation locks) are a wonderful tool for brewing. They allow CO2 gas to escape while preventing anything else from getting into your beer. The cap should be attached once you have added your neutral spirits or cleaner. If you find your fermenter did not have a completely airtight seal it does not mean your beer is ruined. Luckily CO2 is heavier than air, so as CO2 is produced by your fermenting beer it naturally creates an oxygen protective blanket. It’s almost like the beer is trying to protect itself.

Read More About Fermentation:

Cold Crashing - So what is brewing yeast anyway?

Controlling Fermentation Temperature - Make sure your yeast is happy with the temperature. 

Stuck Fermentation - Helpful tips to get your fermentation rolling.  

How To Ferment For Higher Gravity -  If you’re making a high ABV beer, read this.