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Secondary Fermentation

The term Secondary Fermentation typically refers to the period post-primary fermentation where beer is transferred from the primary fermentation vessel to a “secondary” vessel and given additional conditioning time. However, as the circumstances of brewing and materials available have changed, so have opinions on secondary. Transfer to a secondary vessel is largely considered unnecessary, and some brewers consider it risky. In most circumstances Secondary Fermentation can be translated as “The period after primary fermentation has ended and before packaging (whether kegging or bottling).” 


Why were secondary’s originally used?

The practice of secondary fermentation originally had a couple of primary purposes. The first was to prevent off flavors due to autolysis. In the earlier days of homebrewing there were less strains of yeast commercially available to homebrewers and that yeast wasn’t as viable and healthy as it is now. Autolysis is a common cause of off-flavors in beer, and is caused by dead yeast cells rupturing. So, less vital, less healthy yeast meant an increased chance of autolysis, and so transferring the beer off of the yeast into a secondary vessel was one way to prevent those cell ruptures from producing off-flavors in the beer. Another reason for using a secondary was for clarity purposes. Taking the beer off of the yeast and allowing additional time for matter to settle out of the beer resulted in; you guessed it, a clearer beer. Finally, a secondary fermenter was often advocated for during the use of fruit, dry hops, or other additions post-primary fermentation. Because of the shape of most fermenters (think carboys), just dropping fruit or pieces of wood into the fermenter can cause splashing and oxidation. Carefully racking the beer into a new vessel that already contains the new additions can help prevent this oxidation.

Why shouldn’t we be using secondary anymore?

The concerns that originally led to secondary fermentation are valid, but the homebrewing world has changed significantly over a short period of time. Autolysis is no longer as great of a concern for the average homebrewer. Yeast is healthier and more viable. Our fermenters are (typically) not close to the scale of a commercial brewery and the pressure on the yeast isn’t nearly as intense. As such, autolysis is not as common as it once was. John Palmer and Jamil Zainasheff in the March 22, 2010 episode of Brew Strong say that leaving beer in primary for a month is fine and that modern fermentations are healthy enough that neither of them advocate for the use of a secondary vessel any longer (Zainasheff 2010). I’ve personally left beer on the yeast in the primary fermenter for five months with no problems at all; healthy yeast has really changed the brewing game.

As for clarity, there just isn’t enough evidence to back up the claim, or at least, not enough evidence that clarity is a result of using a secondary vessel. If you give the beer more time, then more yeast will drop out, and you will get a clearer beer. In an exBEERiment, Marshall Schott of Brulosophy tested whether or not the use of a secondary affected clarity, and most testers found no discernible difference between the two batches. Some people still argue that using a secondary fermenter produces a clearer beer, I recommend testing both out and seeing which method you prefer. For some additions I agree it is appropriate to rack to a new vessel. I wouldn’t want to dump a bag of cherries into a carboy, too heavy. Dry hops, however, go straight into the carboy and many brewers have no problems at all with this method. Here is the major problem with using a secondary: Off-Flavors. Removing the beer from the yeast before fermentation is fully finished means that the majority of the yeast won’t be able to help in the processing of chemicals that cause off flavors like diacetyl. Transferring also increases the risk of contamination and oxidation, since you are exposing your beer to more equipment. Obviously this can be avoided with careful technique and sanitizing methods, but the increased risk isn’t worth a method which may not produce a better, clearer beer. For most beers, a secondary vessel is entirely unnecessary, possibly detrimental, and not beneficial in any way.

So when should I use a secondary fermentation?

There are a few times when using a secondary is the best choice:

  • When you are bulk aging for an extended period of time. While autolysis is not nearly as much of an issue as it used to be, it is still a possibility, and leaving a beer on the yeast for a long time can certainly cause it. Like I said, I’ve left beer on the yeast for five months with no off-flavors, but that may sound too risky for some brewers. Palmer and Zainasheff say that a month is absolutely fine, and so a month is a good number to start with. Bulk-aging for a month or two? No need for secondary. Longer? That is up to you, but eventually autolysis will be an issue.
  • When using large additions in a bottle-neck carboy. Cherries, raspberries, oak cubes, just dropping these things through the neck of the carboy can cause some oxidation issues from the splashing and oxygen exposure. Racking onto these additions in a secondary vessel may be a safer option. If you have a bucket as your primary fermenter, just gently add the additions since you have more space to get them closer to the liquid.

Hopefully the information here has helped inform you not only what Secondary Fermentation refers to, but the affordances of using a secondary vessel in your brewing.