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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  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.


  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,

    • John


      Many thanks for the comment.

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


  3. Jamie

    Great information, I am new to brewing . I have started with two kits that recommend the secondary fermentation method and have hopefully done them without any problems. I plan on a fruit beer next , would you recommend a secondary on that ?

    • John


      Thanks for the question. I haven´t really brewed any fruit beers (I’m not that fond of drinking them!) so can’t offer advice based on experience.

      If I were to do it I think I would probably use a secondary fermenter, putting the fruit in the bottom and transferring the fermented beer on top. That seems the “cleaner” way of doing it, giving the fruit chance to ferment completely separately from the main beer.

      But I suspect you may get the same result by adding the fruit to the first fermenter after a week or so. It would be worth trying both ways.

      Sorry I can´t be more help.

  4. Jamie

    Thanks John , any information is welcome being new to brewing.

  5. Stuart duke

    Hi John,

    Thanks for your explanation of secondary fermentation, I’m very new to home brewing, this is my second batch only.

    I have a question. On my first batch I brewed until the OG was as instructed but the beer tasted rather flat, I bottled most of the batch adding sugar for secondary fermentation in the bottles, the bottled beer was more gassy after a few weeks and I preferred this liveliness rather than the flat tasting beer.

    My question is, if I prefer my beer like this is it OK to bottle and use secondary fermentation in this manner? I am aware I may have used too much sugar and over-carbonated my beer put I prefer it this way. Do you foresee any problems doing this?


    • John

      Hi Stuart,

      There shouldn’t be a problem with that, unless you use too much sugar and the beer becomes over-gassy. Then there is the possibility that the bottles will explode.

      The purpose of secondary fermentation is to make sure the yeast has finished making the beer in the first place (which may not be exactly when the gravity has reached that predicted), and to give it time to ‘tidy up’ the flavour. Whether you give it this chance or not is a separate question to whether the beer is flat or carbonated. That’s about priming.

      In my experience the beer almost always tastes better if I’m patient so, even if you want highly carbonated beer, it’s probably worth letting the beer sit for a little longer before bottling.

      I hope that answers your question but feel free to ask again if not.



      • stuart

        yes I’ll have to find the sweet spot between high carbonated beer and exploded bottles,
        thankyou for your reply

  6. claude


    I recently brewed 6 gallons of wheat beer using a Muntons extract kit and the instructions that came with it. I think I added about a half gallon too much water to the batch and fermentation is down to a bubble every 10 or 15 seconds.

    I was considering adding maybe a pound more of corn sugar to try to make up for this mistake. I dont know if its too late to try this or not. Any thoughts on this?

    Thanks, Claude

    • John

      Hi Claude,

      It’s not too late to try it, but it depends what you want to achieve by adding the extra sugar. If you’re worried the beer will be watery, extra sugar will make it stronger (in terms of alcohol) but won’t give any more flavour.

      Quantities often end up different from what you expect, so I wouldn’t worry too much about a little extra water.

      Good luck.

  7. Fabian Mulrooney

    Hi John

    I have just brewed a nice all grain Munich Wheat beer. Primary is finished. I have read conflicting info regarding secondary fermentation of wheat beers. Some say you should, some say you shouldn’t. My own thinking is that you should bottle when primary is finished BEFORE too much yeast drops out, as the yeast does provide an important flavor component in this style of beer.

    What do you think??

    Thanks in advance

    • John

      Hi Fabian,

      It’s not a style I like to brew, so can’t comment from experience.

      However, I see what you mean.

      Why not bottle half the batch soon after fermentation finishes, and leave the other half a couple more weeks, or even rack it to a secondary container?

      You would then find out what difference, if any, it makes.

      Cheers, John

  8. Art

    Hi John,

    I’m brewing a chocolate milk stout from a kit. The directions suggest transfer to a secondary fermenter, at which point one adds the 4 oz. of cacao nibs that came with the kit. Is this transfer really necessary or can the nibs be added directly to the fermenting beer. Also, I checked the specific gravity at the beginning and it was 1.051, which accorded with the recipe. But what should the final OG be when the sugar has been converted to alcohol? The recipe does not say.


    • John


      The final gravity will depend on what sort of beer is in the kit. As it’s a milk stout you would expect the final gravity to be relatively high (1.020, say), but it depends.

      The recipe probably doesn’t say because there will be variation from person to person.

      You could add the nibs straight to the original fermenter, but if you’re going to leave them there a long time (for example two/three weeks), it may be worth transferring.

      It feels cleaner adding other flavours after transferring to a secondary, but only a side by side test would prove whether there’s any actual difference in taste.

  9. i am know as Tim

    I am somewhat a newby to homebrew.

    I have been brewing for a year and a half or so. I have brewed around a dozen beers. I have never done a secondary. I was until reading this article under the assumption that secondary was simply a stage were you add other ingredients like juices or extracts after the initial fermentation.

    But now I know I’m wrong. Haha anyway, so as I stated I have never done secondary fermentation and I have never had an issue with off flavors. I have loved every beer I have made and I never found an unpleasant off taste.

    I have never dumped a beer out or had a bad batch because of not doing it. I have only had one batch turn out different than planned and that was a marshmallow stout.

    Not sure why but it came out as a sour. Possibly some wild yeast or bacteria. But it was still drinkable. Just not what I wanted. Currently fermenting a pina colada kolsch!

    • John

      Thanks for sharing your experiences.

  10. Dai Hooper

    Hi John, one wonders if you can advise me. I have got 1x export lager and 1x bitter kit on the go however as I am going in for a new hip I enlisted some help and we both put in a sachet of yeast to the mix (twice as much!) how will this affect the brew/s. I am tempted to just let them run their course am I right.
    Dai H

    • John

      Hi Dai,

      That shouldn’t make too much difference to the brews. Definitely let them run their course!