What to do with a 'stuck' fermentation

Discussion in 'Beer Brewing "How-To" Guides' started by BigYin, Apr 14, 2011.

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  1. Apr 14, 2011 #1





    Dec 31, 2009
    Likes Received:
    Falkirk, Scotland
    'Stuck Fermentation' is one of the most common cries for help on here :hmm:

    In many cases the first answer is "Be patient" :thumb: - the kits may say 4 to 6 days - I've so far found that 10 - 14 days is more like it.

    Check the Specific Gravity

    Has it actually reached a reasonable Final Gravity? Most kits specify a final gravity, as do most AG recipes. If you are a few points above it, that's really not a problem :thumb:

    If you are close to the expected FG, and your hydrometer readings have been the same for three consecutive days, your brew is done :D

    If it is still a good bit off the expected FG then read on.

    Give it a stir

    Sometimes a simple stir will help get those yeasties busy again - use a long handled, plastic, well sanitised, spoon/paddle, and stir gently without any splashing as splashing will introduce oxygen to your beer which may ruin/oxidise it. :nono:

    After a stir, the beer will need time to clear, so leave it the hell alone and let it clear :thumb:

    Again, patience is your biggest ally :drink:

    For your next brew you might like to think about ways to do the initial stir a bit better. The purpose of this stirring is to aerate the wort as much as possible. I have started to use a paint mixer powered by a power drill - it does an amazing job of stirring up/aerating the wort for no effort giving very high levels of aeration, and my fermentations go off like a rocket after this treatment.

    Another option is to bubble oxygen through the wort for a short period at the start of fermentation. The setup for this is beyond my budget, but I know brewers who do this, and it's very effective.

    Check the temperature

    Temperature control might be another problem. Your house might be warm enough through the day - but what about at night? If you can't heat it maybe wrap an old quilt (or dressing gown, or towels??) at night to stop the night time temperature drop. (I use an aquarium heater in mine - and for the FV's I have without a heater, I use a fan heater on a thermostat to keep the room from getting too cold)

    Patience :thumb:

    Don't be afraid to move the FV to a warmer room - or (as I've done before) go buy a heater, fit it to an empy FV, santise it thoroughly, and move the stalled batch into it. Just be rigorous with your sanitising, and try as best you can to minimise splashing and therefore unwanted aeration (this can lead to off flavours).

    To monitor the temperature of an FV, I like the stick on thermometer strips - they're cheap, reasonably accurate for our needs, and you don't have to worry about possibly introducing an infection to the batch every time you stick a thermometer in it.

    Heating your FV

    Several options open to you.
    1. place the FV in a naturally warm place - airing cupboard maybe?
    2. Heat the place it's in with a thermostatically controlled heater (don't want the place like an oven!)
    3. Heat the FV itself :
    a. A brew belt - wraps around the FV - needs some kind of timer or temperature control to avoid overheating
    b. A heated mat - sits under the FV
    c. An immersion heater (I use the glass aquarium heaters as they are designed to be submerged and have their own thermostat) - I place mine in the FV, another option is to use the heater to warm a bath of water that the FV stands in.
    4. Passive insulation - could be a hot water tank jacket, a sleeping bag, a quilt... - anything that insulates well!

    Whatever option you choose, if you are going to actively heat it, to avoid overheating, it MUST be controlled by a thermostat of some description. The aquarium heaters have their own built in thermostat, and the more modern ones are more likely to be accurate enough for our needs, although it's not guaranteed! There are fairly cheap thermostats out there (eg try searching ebay for Mini Digital Temperature Controller Thermostat Aquarium) that will do the job for you.

    Other options :

    Re-Pitching yeast - The one time I did add a fresh pack of yeast to a 'stuck' brew, the SG never shifted anyway after a further week, so whatever was preventing the yeasties from working also prevented the new ones from working :nono:

    Yeast Nutrient - I've never used any, but here's a bit of info on why they work

    Beer Enzyme - sometimes supplied by the kit suppliers to customers who contact them complaining of a stalled fermentation - this will break down some sugars the yeasties can't break down themselves, making more 'food' for the yeast, and allowing the SG to drop. Two warnings though - the fermentation should be allowed to go on for longer than usual to ensure all available sugars have been used up, or the bottle bomb risk is much elevated (see link below), and the resultant brew is also likely to have a drier taste than a similar brew done without an enzyme - this may, or may not, be to your liking..
    http://homebrewandbeer.com/bitsandpiece ... e-test.pdf

    Last Option

    Finally, as a last resort, just bottle, or keg, the beer :thumb: One of my kit beers refused to shift below 1.020 - When it was clear it wasn't going to budge further I bottled it, just adding less sugar for the carbonation, gave it a good long conditioning period (a few months - it was a Christmas brew) and it actually came out as a very nice beer indeed! :drink:
    Last edited by a moderator: Feb 23, 2015
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