Primary and Secondary Fermentation

Transferring beer from a primary to a secondary fermenter. Notice the trub sediment.

I was inspired by this thread on Brew Advice to compile my own findings on primary vs. secondary fermentation and when it’s necessary in the home brew process. Our list of equipment started off with a plastic carboy from Better Bottle and a bottling bucket sans lid. Recently, we discovered you can get airtight lids with a port for an airlock and so now we have the capability of fermenting in either container. In fact, a lot of home brewers go straight for the buckets, as they are often cheap, easy to move around, and block out light.

To tackle this issue, first we have to define what happens in primary and secondary fermentation. Primary fermentation is, in essence, when you start to make actual beer. After your wort has cooled and you add it to your fermenter, you pitch in your yeast and seal the container off. Within hours, the yeast start to eat the malt sugars and as a by-product they create alcohol and carbon dioxide. Now you have beer! Most recipes call for a fermentation of 7-14 days or until fermentation activity has slowed to almost nothing.

In our last post, our Dithyrambic Roasted Brown Ale only called for primary fermentation before bottling. Our next planned brew calls for a secondary fermenter. So why the need for another step?

Well back to the primary fermentation, one of the things that happens when the yeast activity starts to die down is suspended particles in your beer start to settle. The little bits and pieces are made up of inactive yeast, hops, proteins, and other by-products of the brew process. All these things fall to the bottom and create a layer of sediment called trub. The problem with trub is that it can start to affect the flavor of your beer after two weeks, (this is arguable, as I’ve seen sources claiming otherwise, but for now I will assume it to be true) and some recipes call for beer to be aged longer then just 14 days, such as those with high alcoholic content like barley wine or lagers which typically ferment at colder temperatures and longer times than ales.

The other reason to move to a second fermenter, besides aging and separating from the trub, are to induce certain flavors to the beer. One of the most popular methods is dry hopping, which involves adding additional hops directly into the beer without boiling. Other ideas are adding fruit, spices, and oils; although technically by adding these extra ingredients you have not made real beer, according to the German Beer Purity Law.

Second fermentation also aids in clarifying beer, which seems to be an issue to the new home brewer. As long as you have properly sanitized everything when transferring to the second fermenter and it is still sealed, you can be in this step almost indefinitely until you are ready to bottle. Our next recipe will require a primary and secondary fermentation process to flavor our beer.