What Is Secondary Fermentation?

Many brewers swear that secondary fermentation improves their beer. However, this is much debated with many claiming it’s unnecessary.

Here are the arguments for and against.

what is secondary fermentation (fermenting bucket)

Fermentation Overview

Fermentation is a process with various stages.

The first, straight after the yeast are pitched into the wort, is vigorous and builds a foamy head known as krausen on top of the beer. At this point the yeast process the most easily accessible sugars, converting them into alcohol and CO2.

Various hop, yeast and protein waste is also produced, but handily this is removed naturally – the krausen lifts it out of the beer, leaving it stuck dry to the fermenter side as the foam subsides. In this way otherwise unpleasant tastes are removed.

dry hopping : beer after fermentation

Fermentation waste is removed from the beer during the krausen stage (note that the photo is after krausen)

Fermentability of Wort

Malted barley produces many types of sugar, not all of which can be fermented by yeast. The ones that are left behind give the beer sweetness.

Dry beers, such as English bitter, are made from worts rich in fermentable sugars.

As a brewer you can influence the profile of the fermentable and non-fermentable sugars by altering the grains in your recipe. You can also use different mash temperatures to control the sugars that are extracted.

What Is Secondary Fermentation?

In addition to sugar and alcohol, fermentation also produces a variety of other flavour compounds. The degree to which this happens depends on the yeast strain and environmental factors such as fermentation temperature.

These flavours are often considered unpleasant in lagers and other pale beers, but many styles, such as English ale, depend on them for their character.

Some of the off-flavours are undesirable in any beer.

Fortunately the yeast, after performing the initial fermentation, set to work ‘cleaning’ the beer by tidying up these elements. This process is known as conditioning.

Secondary fermentation and conditioning are similar, often interchanged terms.

I think of conditioning and secondary fermentation as one and the same – the second stage in the processing of wort by yeast. Because it improves the beer’s flavour and appearance there’s no question in my mind of its benefit.

The question is whether or not to use a second fermenting vessel.

When To Use A Secondary Fermenter?

Although many brewers transfer their beers to secondary fermenters for conditioning, this is generally agreed to be a waste of time.

After fermenting the available sugars the yeast settle, or flocculate, to the bottom of the fermenter leaving clear beer behind. At this point you can bottle it.

The debris on the bottom is called trub.

If you indefinitely leave the beer sitting on the trub unsavoury chemical reactions will eventually ruin it, or at least add unpleasant flavours. On the other hand leaving it for up to a month or so is unlikely to cause problems, much longer than the time generally required for the yeast to condition the beer.

Those who use secondary fermenters want to eliminate the possibility of damaged beer flavours as a result of too much time on the trub.

However, during transfer you run the risk of exposure to oxygen or bacteria – two more good ways to ruin beer.

The other common argument is that beer conditioned in a secondary is clearer, but in my experience it’s possible to get perfectly clear beer with vigorous boiling and rapid cooling on brew day.

For definitive guidance in times like this I usually turn to John Palmer for answers.

In this instance, his advice is to use secondary fermenters only for lagers or high original gravity beers. In other words, beers that require longer than average conditioning.

Any other beer, and it’s not really necessary.

Secondary Fermentation For High Gravity Beers

I began investigating the issue of secondary fermentation after brewing a very hoppy beer which included an element of dry hopping.

The idea of racking the beer to a secondary appealed because I wanted to leave the dry hops in the fermenter for a long period, and was concerned about extended exposure of the beer to the trub. Additionally, the volume of hops in the recipe made me concerned about blockages when it came to bottling.

Transferring to a secondary fermenter would leave much of the hop wastage behind with the trub.

High gravity beers take longer to condition. Secondary fermenters let you leave them without worrying about off-flavours coming  from the trub.

Should you Use a Secondary Fermenter?

Other than with the aforementioned dry hop technique I rarely use secondary fermenters. Even without whirlfloc or irish moss, I’m able to get clear beers without noticeable off-flavours.

It’s not necessary to use a secondary fermenter for most beers.

What do you think?

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Comments...

  1. terry sparrow

    Dear sir, as a complete novice brewer, I am concerned that my first beer batch may get contaminated by oxygen. Or contamination from dirty equipment. I therefore prefer to leave it in the air tight container with air lock for as long as possible and therefore keg when ready to drink. I am not too concerned about the extra alcohol content by the extra sugar. Also by removing the lid to take specific gravity readings this also risks contamination.

    Why risk removing the lid if not vital? All info appreciated. Cheers

    • John

      You’re completely right. Every time you open the lid you risk contaminating the beer. It’s best to open the fermentor as little as possible and, when you do open it, sanitise everything that touches the beer.

      But I still think it’s worth taking gravity readings after fermentation, even if you’re not concerned about alcohol content. If you don’t, you probably won’t really know if the fermentation is complete.

      If you plan on repeating a successful batch, it’s useful to have as much information about it as possible, including final gravity.

      The important thing is to limit the number of gravity readings, and to wait until there’s a pretty good chance that there’ll be something worth measuring (i.e. after two weeks fermenting).

      Hope that helps.

      Cheers!

  2. Rex

    Hi John,

    Many thanks for your simple yet detailed and unbiased explanation. I’ve read the views from supporters of secondary fermentation and I now believe I can differentiate the purist from the logical!

    With gratitude,
    Rex

    • John

      Rex,

      Many thanks for the comment.

      I’m all in favour of a logical approach to brewing.

      Cheers!

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