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Old 05-12-2017, 10:23 AM   #1
terrym
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Default Simple strategies for dealing with stuck fermentations

A 'stuck' fermentation is normally used to describe a primary fermentation where fermentation stops at a higher specific gravity (SG) than would have otherwise been expected, in spite of the presence of fermentable sugars. In short the yeast gives up before it should. An example of this would be where the SG stops at 1.020 when 1.010 would normally have been expected. There are a number of suggested reasons for this occurring which include an inadequate quantity of pitching yeast, use of old or poor quality yeast at pitching, fermenting temperature too low, and an inadequate quantity of dissolved oxygen in the wort needed to initially promote healthy yeast growth.
The most widely reported case of stuck fermentations is associated with the Woodefords Wherry kit manufactured by Muntons, which comes with a 6g packet of yeast. Some Wherry brews seem to stick at about SG 1.020, and many experienced homebrewers believe 6g of yeast is not enough to guarantee a successful fermentation of 20+ litres of wort under normal brewing conditions, although in fact the yeast itself may be fine and appears to perform satisfactorily when pitched into brews of say 15 litres and less.
There are a number of strategies that have been suggested to restart a stuck fermentation, although the lower the SG the less likely it will be to get a fermentation going again. So it may be very difficult, perhaps impossible, to restart a stuck fermentation at SG 1.015, whereas if the SG is 1.022 there is a good chance. However even with these tried and tested strategies success is not guaranteed, and each case is different governed by local conditions.

So, suggested strategies include:-
1. Rouse the settled yeast by gentle stirring with a sanitised spoon without drawing air into the beer, or give the FV a swirl with the lid in place
2. Raise the temperature of the beer e.g from 19*C to 22*C.
3. Add a sugar solution to the beer, say 100g of sugar dissolved in boiling water, and then gently pour into the beer when cool.
4. Add a teaspoon of yeast nutrient
5. Repitch with fresh yeast.

And in the case of homebrewers considering brewing a Wherry kit or others from that range the advice that is normally provided is to replace the yeast, say to a Nottingham type, or double up the quantity of kit yeast packets used.

Finally if the fermentation refuses to restart there is a simple choice to be made, dump it or keep it. The decision regarding dumping will be primarily governed by taste, too sweet with unfermented sugars and it may be unpalatable. That choice is down to the individual. However if the brew is to be kept it is essential that sufficient time is given to allow any fermentation to restart in the FV before packaging, perhaps at least a week maybe two, since the possibilty of a fermentation restarting after packaging can be disastrous, and for that reason, if the beer is packaged into bottles at least one bottle should be PET so that bottle pressure can be monitored.
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Old 05-12-2017, 10:39 AM   #2
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Hi!
You've missed out: kick the offending FV down the garden while muttering deprecations under your breath.
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Old 05-12-2017, 10:44 AM   #3
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Nice guide Terry, for the perennial question of 'what to do with my stuck wherry.' I've stickied your stuck fermentaion guide
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Old 05-12-2017, 11:37 AM   #4
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Out of interest has anyone ever tried an Alcotec Re-Start Yeast as per this guide?: https://www.the-home-brew-shop.co.uk...rmentation.pdf
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Old 05-12-2017, 01:26 PM   #5
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Nice one terrym!
And of course call chippy tea....forum jedi master.....
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Old 05-12-2017, 01:33 PM   #6
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Yep, thank you Terry. Informative.
If I could also add. Racking your beer after a couple of weeks in primary into another fv can also restart fermentation (prob the same as stirring really) but with the advantage of getting your beer off the trub (but that’s another debatable point...).
I have often found I can knock a couple of points off the sg even when it’s down to around 1014 or so, often even more.
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Old 05-12-2017, 05:01 PM   #7
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Quote:
Originally Posted by Redron View Post
Yep, thank you Terry. Informative.
If I could also add. Racking your beer after a couple of weeks in primary into another fv can also restart fermentation (prob the same as stirring really) but with the advantage of getting your beer off the trub (but that’s another debatable point...).
I have often found I can knock a couple of points off the sg even when it’s down to around 1014 or so, often even more.
This is a good point. Breweries rack their beer; is oxygen a big worry for them?
Also, brewer's yeast produces alcohol under sufferance and is a way of working in low oxygen conditions, in a very similar our muscles produce lactic acid when the muscles aren't getting enough oxygen. Perhaps, a little oxygen on racking will help the yeast restart, too.
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Old 05-12-2017, 04:46 PM   #8
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Good post.

There is a sixth option. Enzymes. Yeast consumes the simplest sugars first, so when a fermentation sticks it is reluctance to consume the most complex sugars that is the cause. These sugars can be reduced to more simple sugars by enzymes, as they are in the mash. A dose of amylase or even hops should do it. The downside is, if it works there will be less dextrines remaining in the beer, leaving it drier.

Also, if adding new yeast it is more likely to succeed if you get the yeast fermenting first with a small starter, and pitch at krausen.

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Old 05-12-2017, 04:56 PM   #9
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Quote:
Originally Posted by Sadfield View Post
Good post.

There is a sixth option. Enzymes. Yeast consumes the simplest sugars first, so when a fermentation sticks it is reluctance to consume the most complex sugars that is the cause. These sugars can be reduced to more simple sugars by enzymes, as they are in the mash. A dose of amylase or even hops should do it. The downside is, if it works there will be less dextrines remaining in the beer, leaving it drier.

"Inspiration is the impact of a fact on a well-prepared mind" Louis Pasteur
What do you mean by hops? So if you were to say dry hop a stuck fermentation it may get it going again?
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Old 05-12-2017, 05:53 PM   #10
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What do you mean by hops? So if you were to say dry hop a stuck fermentation it may get it going again?
Yes, exactly this, combined with the steps outlined by Terrym. Part of the reason why hops Are/were often added to casks, 'hopping down', in rates that would make very little impact on flavour or aroma. Particularly in the case of IPAs that were aged for a year before being shipped to India.

http://www.browneandbitter.com/2014/...tatic.html?m=1





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