Why is My Beer Flat?

There’s nothing worse than opening your long awaited bottle of home brew only to find the beer flat and lifeless. Thankfully it’s easy to make sure this doesn’t happen.


why is my beer flat
If you understand why beer has gas in the first place, you can prepare the conditions necessary for it to form.

Why Beer has Gas

The bubbles in beer are produced by yeast as they convert sugars to alcohol and carbon dioxide gas during fermentation.

The gas is normally released from the fermentation bucket through the airlock (signalling to the brewer that fermentation is in fact taking place) so the beer has very little gas at the point of bottling.

If you try the brew at this point it will taste like flat beer.

How to Add Gas to Beer

To add gas to the finished beer, home brewers introduce priming sugar during bottling.

The yeast suspended in the beer ferment these sugars while inside the bottle. Because the bottle is sealed, the gas stays and becomes an integral part of the beer.

Generally, there are two ways of adding the priming sugar: as a solution mixed with the whole batch, or in small quantities put straight into each bottle.

Priming Solution

A sugar solution of approximately the same gravity as the beer is mixed (and boiled) and gently stirred into the wort. A typical mix of cane sugar for a 20 litre batch is approximately 110g.

It’s then left to settle for twenty minutes before bottling as normal.

Because you rely on dispersion for the sugar to evenly mix into the beer there’s potential for some bottles to be more carbonated than others.

Often, flat beer comes about for this reason. Don’t be impatient - allow the sugar time to mix into all parts of the wort.

It’s vital in this process that all equipment is sanitised and nothing is allowed to infect the beer.

Every time you mess with the beer there’s a risk of contamination from wild yeast or other bacteria.

Spoonful of Sugar

Some home brewers drop a spoonful of sugar into each bottle before syphoning the beer.

This method is easy but fairly inaccurate and can lead to flat beer or overly gassy brews.

Too much sugar causes excess gas which can potentially explode the beer bottles. The risk of contamination to the beer is slightly less than with a priming solution because no additional liquid is added.

Unless you’ve got a good reason not, avoid this method if you’re hoping for consistency between brews.

Carbonation Drops

Carbonation drops are a variation on the spoonful of sugar method.

These tablets of brewing sugar are put into each bottle to give a standardised dose. The drops ensure that each bottle carbonates equally and avoid the need to prepare a priming solution with the sanitising that that involves.

Of course, you’ll still need to sanitise the bottle tops and syphoning equipment during bottling.

The downside of carbonation drops is the lack of flexibility in terms of flavour.

It’s often interesting to add sugars that complement the beer, such as brown sugar to a dark bitter or honey to a summery ale.

On the other hand, the carbonation drops are flavourless so are a good general solution to a problem.

They’re possibly the easiest way of consistently carbonating home brew, but offer little flexibility.

I’ve Correctly Primed. So Why Is My Beer Still Flat?

If you knew all of the above already, have primed your beer correctly yet still wonder why you have flat beer there are a number of possibilities you could consider:

  • The yeast may have settled to the bottom – shake and see if that solves it (a solution from John Palmer)
  • The yeast may not have worked yet – it often takes up to two weeks for the yeast to finish production. This is often the case if the home brew releases gas when opened but has little head retention.
  • The temperature is too low for the yeast to work effectively. Either move the beers to a warmer area or wait longer.

If you’ve followed the steps above it’s just a matter of patience.

Now you won’t have to worry about flat beer again.

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Comments...

  1. ken narbey

    Have been brewing for years with increasing success until two consecutive brews have failed to carbonate during secondary ferment. I know all the basics and have changed nothing in my system. Can you offer any advice ?

    • John

      Hi Ken,

      It’s strange that it should suddenly stop working if you’ve changed nothing in your system.

      Can you be more specific about your process: How do you add priming sugar? Do you bottle or keg? Is the secondary ferment in a cask? etc. Basically, what did you used to do to ensure carbonation?

      Cheers,

      • George M

        I have been brewing for over 20 years without a hitch until recently. I keep getting flat beer – tastes fine, no fizz. The only change is that I am using a new silicon seal to stopper my Grolshe bottle (used for the last 15 years). Any ideas?

        • John

          Hi George,

          On the face of it it sounds as though there’s something wrong with your new seals. Have you tried a batch using ordinary bottles and metal caps, just to eliminate the possibility that the bottles are the problem?

          If not, are you leaving it long enough? I’ve had batches that I thought had failed to carbonate after three weeks but which after two months have turned out fine.

          Otherwise, feel free to leave more information about how you carbonate the beer as that may suggest another cause of the problem.

          Cheers!

  2. Just brewing my first home brew ever!! I’ve got to the stage where I’ve transferred to a pressurised barrel and it’s a case of waiting for things to settle and hopefully get some gas going. Getting impatient though.

    • John

      Hope it turns out well! It’s worth waiting as the beer tends to improve after a little time conditioning.

  3. Lee Darby

    Hi, I have just completed my first brew, from a starter kit bought for me at Xmas. I followed the instructions to the letter. It’s now 3 weeks since I transferred the bottles to the fridge after leaving them standing for 4 days at room temperature.

    I am getting different results from each bottle. Some are completely flat, others are fizzy, and one I opened yesterday had yellow lumps floating around in it like curdled milk. All of them are cloudy so far. I have opened 6 bottles in total out of the 22 I produced.

    Any advice on what might be happening please?

    Lee

    • John

      Hi Lee,

      Was it a beer kit (a tin of hopped malt extract that you added sugar to) or a starter kit of ingredients that you brewed yourself?

      Something that jumps out from your question is putting the beers in the fridge so soon. It usually takes two/three weeks at room temperature (c. 21°C) for the yeast to carbonate the beer properly. You might have chilled the beers before they’d finished.

      Try slowly warming the bottles back to room temperature and leaving them a few more weeks. If the yeast have settled to the bottom you might need to gently shake them back into the beer as well.

      Another possibility, if you used priming sugar, is that it wasn’t mixed into all of the beer. Or perhaps the bottles with flat beer aren’t sealed properly.

      The curdled milk (does it look a bit like bread dough?) could be yeast that hasn’t dropped to the bottom. With time it should fall out, but the important question is whether the beer tastes and smells alright. If not, it may be something more unpleasant.

      In my experience, unless the beer’s clear when you bottle it cloudiness can take anything up to two/three, sometimes more, months to go. But it nearly always does, assuming the beer’s OK.

      The short answer to everything is give it time.

      Hope that helps!

      • Lee Darby

        Also, the lumps did look like bread dough yes.

        Just find it odd to be getting such different results from the same set up.

  4. Lee Darby

    Hi John

    It was a starter kit with a tin and 2 separate packets of yeast. I followed the instructions on the kit.

    I mixed the ingredients in the FV and left in a warm room for 7 days. After the 7 days I sterilised the 22 plastic bottles that came with the kit. I then added a level teaspoon of normal white household sugar to each bottle and syphoned the brew into the bottles, leaving approx 1 inch at the top of each bottle.

    The instructions said to leave in a warm room for another 4 days in the bottles then transfer to the fridge for 2 weeks. So in total the duration was 25 days from adding to the FV to testing the beer.

    Thanks for the help,
    Lee

    • John

      Hi Lee,

      Yes, it’s strange that the results varied from the same starting point. That said, there’s usually a bit of variation just because yeast’s a live element that may not behave exactly as expected.

      Normally I’d leave the beer at least two weeks before bottling, and then expect to wait another two or three (at room temperature) before the gas builds up. I’d bring the beers out of the fridge for a few weeks and see if that fixes the issue.

      I’ve only brewed one beer kit (before starting brew in a bag) so am far from expert, but I think they sometimes underestimate the time for doing everything. In my experience time solves many problems.

      Hopefully you haven’t been put off brewing. It’s really great fun once you get into it.

      Good luck!

  5. Lee Darby

    Thank you John.

    No it hasn’t put me off.

    In fact, I’m going to purchase some ‘milestones crusader’ at the weekend and give that a whirl.

    I am going to take the remaining bottles out of the fridge this evening and transfer to the garage for a few weeks.

    I will buy a king keg at the weekend for the crusader to go into, and basically give it more time as you say. It’s a learning process.

    My friend began homebrewing in October and has successfully done 9 different brews so far, so we are getting quite into it together.

    All the best for now!

    Lee

  6. John,

    I brew from a kit and do the two stage fermenation process. Then, after two weeks, it goes into a cornelius keg with co2 at 30 lbs for a week. The back down to 8-10 lbs and then tapped to drink. It seems flat. What did I forget? Gale

    • John

      Gale,

      I don’t (unfortunately) use Cornelius kegs so can’t really offer any advice.

      From what little I know, it sounds as though you’ve done it about right. Have you checked for leaks?

      Sorry I can’t be of more help.

      John

  7. You can improve on the ‘Spoonful of Sugar’ method by using sugar cubes. One cube = 1 tsp of sugar, no worrying about measurements or spilling sugar.

    • John

      Thanks for the tip, Jim.

      That’s a handy variation on the carbonation drops option, although personally I prefer to make a priming solution as that gives a bit more control. High or low carbonation depending on the type of beer.

      Cheers!

  8. steven dodsworth

    Hi, I am brand new to home brewing and have just bottled my first batch of coopers canadian blond lager, I have followed the instructions to the letter, I primed the bottles with sugar and filled them yesterday, when I looked today the brew just looks completely flat with no bubbles in the bottle whatsoever. Is this normal at this stage, Thanks for your help.
    Steven

    • John

      Hi Steven,

      Yes, that sounds normal. You never really see gas or bubbles through the bottle unless the beer’s been shaken up, even after a couple of months, so you won’t know if the beer’s flat or not until you open it.

      In my experience it takes about two weeks for the carbonation to complete. After a few days you will probably have gas and foam, but it won’t last long after pouring.

      The best thing to do is wait a couple of weeks and try then.

      Good luck!

  9. Evan

    Hi there. Me and a friend are brand new to home brewing and we just finished up a batch of India pale ale that turned out great. We strictly followed the directions with this first batch but now I want to try making a stout from one of the pre-made kits, but I want to try giving it a maple syrup flavor. Would I add the maple syrup in when I’m originally putting it into the fermenting bucket, or when I am bottling it? Also, exactly how much syrup would I need to make 23L batch? Could I do a mix of maple syrup and dextrose?
    Thanks a bunch for your help. Your website has already given me some interesting ideas.
    Cheers
    Evan

    • John

      Evan,

      I’ve not added maple syrup to a brew before so can’t offer much specific advice.

      I imagine it would behave similarly to honey, which is best added after the main fermentation has finished. Before then most of the flavour is lost.

      You can add it directly to the bucket where it will ferment and increase the strength, as well as adding flavour. I expect you need a fairly large addition, to make up for the loss to fermentation.

      You could also add it at bottling, instead of using priming sugar. On it’s own I doubt this will affect the flavour that much but it’s nice to be consistent with ingredients. You could do a mix of maple syrup and dextrose, but you may want to test how much maple you’re getting first. The sugar won’t help if you’re short of flavour.

      I usually find with these things any advice you find won’t be specific to your ingredients and beer recipe, and that it’s best to carry out a few tests of your own.

      I like splitting batches and dosing each one with a different amount of whichever ingredient I want a test. That way, the next time I brew I have a better idea of how the ingredient performs and what I like.

      Sorry I can’t be of more help – good luck!

      John

  10. Peter

    Hi, I have been making lager for a few years now with success most of the time. I now have a problem in that the beer is flat after a month. Its a Mexican Lager that made up the mixture as per instructions. I waited for two week for the first fermentation to finish. I left it longer then usual to let the sediment settle and reduce the amount in each bottle. I then add one carbonation drop to each bottle. I left the bottles in a warm place for a week before moving. It is possible that I left the first fermentation for too long and there was not enough yeast to start the second fermentation?
    Any advise?
    Regards,
    Peter

    • John

      Peter,

      If it’s only been a month since you brewed it would be unusual for all the yeast to have settled out. Or did you do a long lagering stage?

      In any case, one week is a little short for the carbonation to take place. I leave it for around three weeks because usually some bottles take longer than others to complete. It could just be that you haven’t waited long enough.

      If that’s not it, are all the beers flat or just some of them? Are you sure there’s a good seal on the bottles?

      John

  11. Scott

    I have brewed 5 different. Ale kits and 2 of them had the same problem with carbonation so what I have started doing is after first week of bottling I will ” gently ” turn the bottles over to unsettle the yeast and the let sit and settle back out and this has worked on past 2 batches, don’t shake though hope this helps!

    • John

      Thanks for the suggestion, Scott.

  12. helen oxley

    i have been brewing my own lager in kit form from fermenter to barrel with only 3oz of cane sugarto prime then after two days bottling. yuk flat horrid lager.after reading your site i had already bottled the lager,would it be ok to add caster sugar as primer in the bottles a day late ??

    • John

      Yes, you can open the bottles and add sugar if you’re sure you haven’t primed enough. Otherwise I’d leave it a bit longer to see if it improves first.

      Opening the bottles introduces another chance for the beer to get infected. It should be OK, provided you sanitise the bottle necks before and after opening, as well as all equipment and the new bottle tops.

      Hope the beer turns out OK!

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