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Final Gravity

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sluggerdog

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Hey All,

Just a few questions on the final gravity and where/what it should be. Does it depend on the ingrediants, the temperature, the original gravity?

Is there a range that things should start and finish at?

For Example, I put down a batch 7 days ago and the starting gravity was 1.040, I measured it yesterday and it was down to 1.012, I am still going to leave it there for a while as I thought it has to be down to 1.005 as it states on the can however after doing some searching it seems the final gravity can finish in different points.

Thanx
SD :)
 

dreamboat

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slugger,
you are generally right, the finishing gravity is related to a lot of things:
Original Gravity - only a portion of the OG will be fermented out
Ingredients - some ingredients are less fermentable than others
Yeast strain - certain strains of yeast will ferment out further than others.
Temperature of Mash (or minimash) - hotter mash will be less fermentable
Health of yeast - a good strong yeast population will get the gravity down further than a poor batch.

I am sure that there are a couple more which someone will bring up.

I think that if you follow the instructions as they are given on the can, and add a kilo of sugar to your basic can, you will get down towards 1005, but in my experience, you would be more likely to get to 1008ish.

If it is stable at 1012 for several days, then you are generally safe to bottle at that point. I have bottles strong beers as high as 1020+ and I am not concerned about bottle-bombs.


Dreamboat
 

sluggerdog

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Thanks Dreamboat..

So basically to sum up, if it has been stable for a few days it is safe to bottle, no matter what it is.... CORRECT?

How about % of alcohol, is this determined by either the differance or how low it goes?

Cheers
SD :)
 

dreamboat

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Not necessarily...
If you brewed up a kit and kilo, and it only dropped to 1020, then there is a problem of some sort, maybe fermentation temperature or whatever, which has affected the yeast. So you kind of need to know in advance what to expect before you bottle it.
For most yeasts, 75% is reasonable attenuation, so a drop from 40 to 10 is about right. Dropping to 12 is probably acceptable is you have looked after your yeast, but in the 15+ range, I would suggest that something has not gone quite to plan.
That said, I bottled a stout at aroun 1018 (1052og) which was probably still a little on the high side... but I had gone through the full process of making sure fermentation was finished, including 3 weeks or more in secondary, warming the brew a little, adding more yeast, rousing the yeast.... when that was all done, I could be confident that it had run its race. Now after 3 weeks on the bottle, it is carbonating up nicely, and will be a great brew in another couple of weeks.


dreamboat
 

dreamboat

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% alcohol determined by the difference between og and sg.


dreamboat
 

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Sluggerdog
For kits and bits brews there is a good calculator on the brewcraft site
here

In the sg calculator you can put in your ingredients and it works out what the starting gravity should have been, and guesses what the final gravity should be, applying some sort of average attenuation. It takes account of things like dried corn syrup which raises your final gravity quite a bit.

I wouldnt use it to tell you when the brew is finished, but if your gravity is close to that predicted, AND it has been stable a few days, then you know you are OK.
 

sluggerdog

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Thanks Guys, the calculator said it would come out at at bout 1.013 so I'm sweet, will leave it til thursday to be sure!

CHEERS
SD :D
 

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