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Home Brew Forums > Home Brewing Beer > Fermentation & Yeast > What determines Final Gravity
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Old 01-05-2011, 03:22 AM   #1
vindee
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Default What determines Final Gravity

I'm used to fermenting wine and having it go completely dry during primary, but I'm new to the brew seen. I'm wondering what determines your final gravity? Do you let fermentation go to completion on it's own or do you stop it at a specific gravity?
I know the recipes give you a FG but I need a little more explanation on how that's achieved.
Thanks
Steve

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Old 01-05-2011, 03:26 AM   #2
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There are severable variables that affect FG. A few of them are:
mash temps
yeast strain
pitching rate
aeration & oxygenation
fermentation temps
amount of fermentables & unfermentables
etc. etc.

Good luck, and welcome to the HBT community
Happy Brewing!

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Old 01-05-2011, 06:05 AM   #3
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as mongo said, many things go into what the actual FG will be. for recipes, its usually just based on the average attenuation of the yeast strain used.

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Old 01-05-2011, 06:46 AM   #4
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+1. Type of grain is another variable. As far as an all-grain brewer goes (starting from the malted grain (and sometimes unmalted), and not the malt extract made by a company), all the variables are adjustable. Type of grain, mash temp, whether you use nearly 100% fermentable sugars like cane or corn sugar, yeast strain, amount of yeast pitched, ... These variables all determine what the FG will be.

With extract it's a little more limited to the brewer, but not entirely. Basically there are just more unknowns. If it's malt extract, whether it's dry (DME) or liquid (LME), it is made of grain originally as well. But it's hard to know what type of grain the malt company used to make the DME or LME; for instance, how much crystal malts were used to make an "amber" DME? Also, what was the mash temp they used? and (i'm assuming this matters to how well malt extract ferments) how did the company dry the "wort" so it was concentrated dry or liquid extract (i.e. whether there was caramelization that made some of the sugars that were fermentable into unfermentable)? Also, how old is the extract? Has it degraded on the shelf and might not be as fermentable as it was when it was fresh?

Regardless, I think it is safe to say that beer brewers don't (generally) stop fermentation purposely. It can all be (if all goes well) determined by ingredients and process.

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Old 01-05-2011, 02:22 PM   #5
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Thanks for the replies everyone,
So in other words just let it go and it will finish where ever it will based on the mentioned variables.
Thanks again
Steve

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Old 01-06-2011, 04:45 AM   #6
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"So in other words just let it go and it will finish where ever it will based on the mentioned variables."

Pretty much it. After a few more brews, a bit more experience, and a little reading.... you'll be able to manipulate the aforementioned variables and get close to predicting exactly where it will end up. Have fun and good luck.

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