Secondary Fermentation, Pros and Cons

by Al Folsom
When we start new brewers off at Keystone, the process includes fermenting the beer in a plastic bucket, siphoning (racking) to the bottling bucket, and bottling. The process is kept as simple as possible so that the new brewer gets good beer, and gets it as quickly as possible! Sooner or later, though, that new brewer shows up at a homebrew club meeting, and hears mention of “secondary fermentation,” or something even more cryptic like “I dry hopped it in the secondary,” and their reaction is “Huh?”

Secondary fermentation is the process of taking your “finished” beer from your fermentation bucket, and transferring it to another container, usually a glass carboy, for a period of aging typically ranging from two days to several months. There are pros and cons to doing a secondary fermentation for your beer. In some cases it may not be necessary at all, and in others, it is vital to the beer.

Let’s start with the cons. Racking your beer an extra time gives you one more stage to introduce a flavor-detracting infection in your beer. It’s another process where you have to be scrupulously clean and sanitary. It’s also another time when you can introduce oxygen into the fermented beer, which can lead to cardboard-like or stale flavors. It adds to the cost, since you need to buy an extra carboy. Finally, it introduces another delay before you can drink the beer!

Given the cons, why would anyone do a secondary fermentation? There are a couple of very good reasons to consider doing a secondary fermentation on your beer. The first is probably obvious. It allows the beer to clear more, giving you a better-looking brew, with less sediment in the bottom of the bottle.

But why not, you might ask, just let your beer sit longer, in the primary fermentation bucket? Because plastic buckets are never fully air tight, and once the primary fermentation has slowed and is not producing large amounts of protective carbon dioxide, oxygen will affect the beer, producing those stale, oxidized flavors. If we’re going to let the beer sit after its main fermentation is done, it pretty much needs to be in glass, and away from the spent yeast that accumulates at the bottom of your fermenter.

Also, because yeast are clever little creatures, when they run out of that nice yummy sugar to eat in your wort, they will find other things to munch on. One handy source of nourishment is dead yeast cells. Unfortunately, when the yeast go down this metabolic pathway, they don’t produce the carbon dioxide and ethanol that we all know and love. Instead, through a process known as “autolysis” they produce some interesting off flavors, reminiscent of burning tires-definitely something you don’t want in your beer.

But why age your beer so long? In essence, longer aging using secondary fermentation will generally smooth out the beer, giving you a more pleasant tasting brew. In the case of lager beers, this type of yeast requires a long, cold secondary fermentation. As yeast consume the sugars, they leave odds and ends of more complex sugars around, and will eventually turn to them for nourishment. It is not unusual for this process to take a month or more in lagers.

Ale yeasts, on the other hand, cannot process these more complex sugars and therefore require less time in a secondary fermentation. Once your ale has cleared to your satisfaction in the secondary, it has probably also completed any biological benefits from the secondary fermentation. Secondary fermentations for ales are usually on the order of a week or so, though it won’t hurt the beer to stay in the fermenter longer (but remember that hop flavors and aroma may fade over time). “Big” beers, such as barley wines and imperial stouts, may take a long time to finish fermenting, because there is more sugar to consume, and the yeast is struggling in the presence of the higher alcohol content.

Should you do a secondary fermentation? Some brewers only do it for lagers, some only with their “big” beers, and some (like me) for nearly every beer, to help with the clarifying if nothing else. It’s just one more tool to help you make that perfect beer.

Beer Info, Education, How To Brew Beer
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7 Comments

  1. Excellent information ! I have an Irish Stout that looks like mud,because i forgot to add the irish moss. My primary fermentation is almost done. Is it possible to add the Irish moss to the secondary ? Any help would be appreciated. Thank You.

    • Gonzalo says:

      Yes you can add something like gelatin that has been mixed in warm sterilised water and added to the secondary, You will need to leave it 4-5 days for the gelatin to do its work before bottling or kegging.

  2. Laurie Sobel says:

    I am finishing up a Belgian dubbel. Would you recommend a second fermentation? I have a 6.5 gallon carboy, will this be to large (allowing to much air in)?

    Thank you

    • Keystone says:

      Hi Laurie,

      A secondary fermentation isn’t necessary for a Belgian dubbel, but it would help to ensure that the fermentation is fully finished and the beer is clear. As this article suggests, you should consider both the pros and the cons. The 6.5-gallon carboy will have too much headspace for a five-gallon batch, unless you plan to purge the headspace to get rid of the oxygen. (If you decide to take that route, this product works well!) If you decide to forego the secondary, a few extra days in the primary fermenter would be a reasonable alternative in this case. Let us know if you have any other questions, and enjoy the beer!

  3. chad picha says:

    Curious, I have an IPA in secondary that still burps every 2 mins. It was in primary for 2 weeks and now in secondary for 7 days. If it’s still active in a week, should I wait to bottle?

  4. Matt says:

    Are you taking hydrometer readings? A cooler fermentation temperature can take a lot longer to finish fermenting. I have had beers in the past that have taken 3 or 4 weeks to fully ferment

  5. Jason says:

    Well Hii guys,

    I had a question. Well, does secondary cold fermentation reduce the sugar levels in the home brewed beer. Actually to be honest my beer accidentally turned out to be an extra sweetly delight and i thought to do a second cold fermentation in case it decreases the sugar level and might as well increase the alcohol level in it .

    Please help if you know how second fermentation works.

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