Kegconnection Complete Starter Kit and More Giveaway!


Home Brew Forums > Home Brewing Beer > Beginners Beer Brewing Forum > Calculating, Specific Gravity and ABV

Reply
 
LinkBack Thread Tools
Old 08-10-2010, 11:38 PM   #1
BVilleggiante
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2010
Location: Petaluma, CA
Posts: 316
Liked 2 Times on 2 Posts
Likes Given: 8

Default Calculating, Specific Gravity and ABV

Hello,

Is there a way to calculate the end specific gravity of your beer? I know you take a reading of the OG before fermentation, but how do you know what the specific gravity should be before it's done fermenting? Also, is there a way to predict the alcohol content of your brew?

Sorry, very new to this. Still reading and haven't even done my first brew yet. I've seen the things above mentioned, but not how to calculate them.

__________________
BVilleggiante is offline
 
Reply With Quote Quick reply to this message
Old 08-10-2010, 11:41 PM   #2
ChshreCat
HBT_SUPPORTER.png
Feedback Score: 0 reviews
 
ChshreCat's Avatar
Recipes 
 
Join Date: Aug 2008
Location: Camano Island, Washington
Posts: 11,240
Liked 453 Times on 360 Posts
Likes Given: 16

Default

I punch all the ingredients into beersmith and it gives me an estimate. You can do the same on the beer calculus website for free. There are a lot of variables so it's just a ballpark estimate, but it's usually close. There's a few different formulas you can use to figure out your ABV based on the OG and SG. I just let beersmith do the math for me.

__________________
ChshreCat is offline
 
Reply With Quote Quick reply to this message
Old 08-10-2010, 11:48 PM   #3
BVilleggiante
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2010
Location: Petaluma, CA
Posts: 316
Liked 2 Times on 2 Posts
Likes Given: 8

Default

I think I'm going to have to look at that software. I've heard pretty good things.

__________________
BVilleggiante is offline
 
Reply With Quote Quick reply to this message
Old 08-10-2010, 11:55 PM   #4
Bmorebrew
Feedback Score: 0 reviews
Recipes 
 
Join Date: Mar 2010
Location: Baltimore, Maryland
Posts: 475
Liked 11 Times on 11 Posts
Likes Given: 5

Default

It depends on how fermentable your sugars are. For example if you mash too high and end up with more unfermentable sugars, your FG will be higher than if you mash at a lower temperature (thus ending up with more fermentable sugars).

__________________
Bmorebrew is offline
 
Reply With Quote Quick reply to this message
Old 08-11-2010, 12:51 AM   #5
BigB
Feedback Score: 0 reviews
Recipes 
 
Join Date: Dec 2009
Location: Shelby Twp, MI
Posts: 1,760
Liked 41 Times on 36 Posts
Likes Given: 41

Default

I agree with the Cat... Beersmith is a great program and has lots of included calculators.

__________________
I love the sound of an airlock bubbling in the morning. It sounds like.....VICTORY.

Quote:
Originally Posted by TxBrew
It's now degenerating into nu uh and uh huhs and it no longer serves a point.
BigB is offline
 
Reply With Quote Quick reply to this message
Old 08-11-2010, 01:02 AM   #6
passedpawn
Moderator
HBT_MODERATOR.png
Feedback Score: 0 reviews
 
passedpawn's Avatar
Recipes 
 
Join Date: Apr 2009
Location: ☼ Clearwater, FL ☼
Posts: 18,262
Liked 3054 Times on 1924 Posts
Likes Given: 2593

Default

1) Typically FG is OG/4. So a 1.040 OG will end at about 1.010. Note that you do the math on the "40" part of the number, not "1.040".

2) ABV = OG-FG / 7.6. So, 40-10 / 7.6 = 3.94%

__________________
I'd love to change the world
But I dont know what to do
So Ill leave it up to you
passedpawn is offline
 
Reply With Quote Quick reply to this message
Old 08-11-2010, 02:59 AM   #7
BVilleggiante
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2010
Location: Petaluma, CA
Posts: 316
Liked 2 Times on 2 Posts
Likes Given: 8

Default

Thanks Passpawn. Even if I get beersmith it's good to understand the math behind it.



Quote:
Originally Posted by passedpawn View Post
1) Typically FG is OG/4. So a 1.040 OG will end at about 1.010. Note that you do the math on the "40" part of the number, not "1.040".

2) ABV = OG-FG / 7.6. So, 40-10 / 7.6 = 3.94%
__________________
BVilleggiante is offline
 
Reply With Quote Quick reply to this message
Old 08-11-2010, 03:26 AM   #8
ajf
Senior Member
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
 
ajf's Avatar
Recipes 
 
Join Date: Oct 2005
Location: Long Island
Posts: 4,643
Liked 99 Times on 93 Posts
Likes Given: 39

Default

Let me correct passedpawn's formula. It should be ABV = (OG-FG) / 7.6. So, (40-10) / 7.6 = 3.94%. The other variation is (OG - FG) * 131, so (1.040 - 1.010) * 131 = 3.93%.
Same formula with rounding differences.
If you know what your OG and FG are, you can calculate the ABV pretty accurately.
The problem comes with predicting what the OG and FG will be.
It is relatively simple to predict the OG given the correct information, but in my experience, some of the extract potentials in Beersmith do not match the data sheets produced by the maltsters. In my case, this results in about a 5% reduction in the OG.
What is far more important is that the prediction of the FG is about 20% higher than I typically achieve. This makes (for me) the Beersmith predictions for FG and ABV to be totally useless.

-a.

__________________

There are only 10 types of people in this world. Those that understand binary, and those that don't.

ajf is offline
 
Reply With Quote Quick reply to this message
Old 08-11-2010, 03:52 AM   #9
BVilleggiante
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2010
Location: Petaluma, CA
Posts: 316
Liked 2 Times on 2 Posts
Likes Given: 8

Default

Thanks Alf. This too is good info and thanks for the info and beersmith. That makes me leery of it.

__________________
BVilleggiante is offline
 
Reply With Quote Quick reply to this message
Old 08-11-2010, 04:03 AM   #10
passedpawn
Moderator
HBT_MODERATOR.png
Feedback Score: 0 reviews
 
passedpawn's Avatar
Recipes 
 
Join Date: Apr 2009
Location: ☼ Clearwater, FL ☼
Posts: 18,262
Liked 3054 Times on 1924 Posts
Likes Given: 2593

Default

Quote:
Originally Posted by ajf View Post
Let me correct passedpawn's formula. It should be ABV = (OG-FG) / 7.6. So, (40-10) / 7.6 = 3.94%. The other variation is (OG - FG) * 131, so (1.040 - 1.010) * 131 = 3.93%.
Same formula with rounding differences.
If you know what your OG and FG are, you can calculate the ABV pretty accurately.
The problem comes with predicting what the OG and FG will be.
It is relatively simple to predict the OG given the correct information, but in my experience, some of the extract potentials in Beersmith do not match the data sheets produced by the maltsters. In my case, this results in about a 5% reduction in the OG.
What is far more important is that the prediction of the FG is about 20% higher than I typically achieve. This makes (for me) the Beersmith predictions for FG and ABV to be totally useless.

-a.
Well, yea, predictions of any kind are useless once you have measured the actual numbers. Until then, they are very useful in designing a beer (IMO). Especially for a new brewer.

I don't think anyone should avoid using beersmith, promash, or any other tool. Brewing is better with them than without them, regardless of some very minor flaws.
__________________
I'd love to change the world
But I dont know what to do
So Ill leave it up to you
passedpawn is offline
 
Reply With Quote Quick reply to this message
Reply


Quick Reply
Message:
Options
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Specific Gravity ? WayneTree Beginners Beer Brewing Forum 1 03-06-2009 08:47 PM
Specific Gravity?? when and how much Eepa Beginners Beer Brewing Forum 7 02-05-2009 12:56 AM
Specific Gravity Unruly Beginners Beer Brewing Forum 16 03-21-2008 10:31 AM
Specific gravity Turkey Man Beginners Beer Brewing Forum 11 06-13-2007 04:25 AM
Specific Gravity Evets Beginners Beer Brewing Forum 4 07-19-2006 04:38 AM