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Old 09-10-2009, 06:04 AM   #1
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Default how to stop fermentation?

I'm doing a stout that calls for a final gravity of 1.016 - 1.020 but I've noticed with my set up that most of my beers finish a lot lower than that, regardless of the recipe. my guess is the temperature in my apartment is quite high but that's just a guess. anyway is it a good idea to kill the yeast when i reach the final gravity i want? or just let them go and hope for the best?


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Old 09-10-2009, 06:15 AM   #2
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Can you post a recipe?

I would not suggest trying to stop the yeast before they are done. You are more likely to leave off flavors, like green apple from unfinished fermentation.

Off the top of my head the three things that might need to be looked at are:

1. Original Gravity - are you starting high enough? If you have less fermentables to start with, the resulting gravity will be lower.

2. Recipe formulation / Process tweak - there are several ingredients and processes that can affect final gravity. Simple sugars are highly fermentable. Crystal malts and dextrin malts are not. If you are all grain, mash temp can also affect it.

3. Contamination - Wild yeast and bacteria can eat the things regular yeast leave behind, dropping the gravity. Check your sanitation techniques.


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Old 09-10-2009, 01:22 PM   #3
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Don't stop the fermentation. You must let the yeast finish their job. If you overshoot your FG it just means you need to adjust your recipe/process. Brewsmith gave a good overview of how to do that above.
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Old 09-10-2009, 03:31 PM   #4
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Easiest thing I can think of for stouts (if your brew was all all grain) would be to mash with high temperatures. Granted that won't help you now, but in the future if you mashed with high temps it would produce more unfermentable sugars, ensuring a higher FG.

As Brewsmith said, pinching the yeast off in mid stream might not be a good idea.
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Old 09-10-2009, 03:51 PM   #5
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Most stout recipes have high percentages of unfermentables from the caramels, and dark roasted grains. Without a recipe, can't say much more.
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Old 09-10-2009, 05:46 PM   #6
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The temp of your apartment should not really influence the final gravity too much. You should be fermenting at the temp that the yeast will perform best at.

Mashing at a higher temp will give you more unfermentable sugars, and therefore a higher FG. Some yeasts will not finish as much as others, so if you are subbing yeast in the recipe, that might be the cause for your batches finishing lower.

If you Keg, and want to stop the fermentation, you can use a camden tablet to kill the yeast, but it's not recommended, as the yeast do more stuff after eating the sugars, like removing certain flavors and creating new ones.
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Old 09-10-2009, 06:29 PM   #7
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If it's too thin you can add malto-dextrine powder for body and/or lactose for sweetness. Most likely as these guys said you need to look at the ingredients/process, or use a less attenuative yeast strain next time.
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Old 09-11-2009, 01:33 AM   #8
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Thanks for the response guys! the recipe is the Obsidian Stout Clone featured on the byo website. here it is:

90 min boil
11.9 lbs - 2 row
1.43 - Black barley
1.1 crystal 80
.66 - carapils
.66 - light munich
.66 wheat malt
.11 - roast barley

1.06 oz - chinook 90
1.06 - willamette 30
1.06 - hallertauer 5

Ringwood Ale Yeast

mash: 150-151

The low mash temp but high FG was what got me thinking about killing my yeast! In the past I've noticed that even when i mash quite high i still finish pretty low. I think I'm going to just brew this as close as i can to what the recipe calls for and take note of what happens.


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