Kegconnection Complete Starter Kit and More Giveaway!


Home Brew Forums > Home Brewing Beer > Beginners Beer Brewing Forum > Will adding alcohol throw FG readings off?

Reply
 
LinkBack Thread Tools
Old 03-09-2011, 01:52 PM   #1
AlanS
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jan 2011
Location: Harrisburg, PA
Posts: 25
Default Will adding alcohol throw FG readings off?

I searched, but most of the results I uncovered were for adding fruits, or honey into secondary, and the resulting change in S.G.

I'm brewing a stout, and added vanilla & Jameson into the mixture when racking to secondary. I don't have my notebook with me, but I know my S.G. at the transfer to secondary was ~ 1.010. After adding 2 cups of whiskey, with the alcohol still in it (read, not boiled off), will my FG readings before bottling still be accurate? In other words, will (OG - FG) x 131 still give me an approximate ABV%, or will the added alcohol somehow alter the reading?

My gut's telling me I'm just overthinking it, and normal readings will be fine, but I'm relatively new to this, so I'm just looking for some reassurance.

Thanks.

__________________
AlanS is offline
 
Reply With Quote Quick reply to this message
Old 03-09-2011, 01:56 PM   #2
Ace_Club
Legendary Influential Brewer
HBT_SUPPORTER.png
Feedback Score: 0 reviews
 
Ace_Club's Avatar
Recipes 
 
Join Date: Sep 2008
Location: Chicago, IL
Posts: 35,345
Liked 1514 Times on 1438 Posts
Likes Given: 52720

Default

The normal readings will be fine for your purposes. This isn't an exact science after all.

However, technically the added alcohol will affect the FG readings. Even the alcohol produced by the yeast affects the FG. The OG is based off of the amount of sugars dissolved in water. The FG is not, however, just the remaining unfermented sugars that are still dissolved in the wort. It also contains alcohol which has a lower SG than water. This combination will give you a lower FG reading than if the alcohol weren't present.

In the end, however, know that as homebrewers we are just looking for an estimate of the amount of alcohol present and the readings you get are fine for that purpose.

__________________
Quote:
Originally Posted by IrregularPulse View Post
I'll make my buddy do it with me next time. That'll make me go harder at it.
"If guns don't kill people, why do we give people guns when they go to war? Why not just send the people?" - Ozzy Osbourne

Sent from my iPhone 4s.

Canon T2i | EF-S 18-55mm | EF 28mm 1.8 | EF 50mm 1.8 | EF-S 55-250mm

3 whipped dog straights, Gillette Ball End Tech, 1959 Gillette Fat Boy

Secondary: Strawberry Melomel
Ace_Club is offline
 
Reply With Quote Quick reply to this message
Old 03-09-2011, 01:56 PM   #3
GilaMinumBeer
In yo' garage, steelin' yo parts.
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
 
GilaMinumBeer's Avatar
Recipes 
 
Join Date: Jan 2008
Location: Oblivion
Posts: 47,004
Liked 4620 Times on 4308 Posts
Likes Given: 56

Default

Yes. Anything added will serve to dilute the mixture. It's no different than adding water with respect to SG except that, instead, you are adding something already fermented.

On another token, adding too much alcohol to the brewer can effect SG readings too.

__________________
GilaMinumBeer is online now
 
Reply With Quote Quick reply to this message
Old 03-09-2011, 01:58 PM   #4
ongreystreet
Feedback Score: 0 reviews
Recipes 
 
Join Date: Nov 2010
Location: Columbia, MD
Posts: 313
Liked 6 Times on 6 Posts
Likes Given: 1

Default

Is your beer done fermenting?

Cause if it is, what's the point in taking another gravity reading?

To find the ABV(Alcohol by Volume) just calculate how much, Alcohol there is in your volume.

__________________
ongreystreet is offline
 
Reply With Quote Quick reply to this message
Old 03-09-2011, 02:03 PM   #5
Pilgarlic
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2010
Location: Tampa Bay, Florida
Posts: 1,295
Liked 123 Times on 96 Posts
Likes Given: 34

Default

Your question was: "will (OG - FG) x 131 still give me an approximate ABV%". The answer is "yes". The final gravity will be lower than it would have been had you not added alcohol, but the equation holds.

__________________
Pilgarlic is offline
 
Reply With Quote Quick reply to this message
Old 03-09-2011, 02:05 PM   #6
ongreystreet
Feedback Score: 0 reviews
Recipes 
 
Join Date: Nov 2010
Location: Columbia, MD
Posts: 313
Liked 6 Times on 6 Posts
Likes Given: 1

Default

Quote:
Originally Posted by GilaMinumBeer View Post
Yes. Anything added will serve to dilute the mixture. It's no different than adding water with respect to SG except that, instead, you are adding something already fermented.

On another token, adding too much alcohol to the brewer can effect SG readings too.
So if something like honey or maple syrup(think that qualifies as anything) is added it will dilute the mixture? What about adding other beer to your beer? If I fill half a glass with Bass and measure the gravity, then fill the rest with Guinness and measure again, it won't change?

It's no different then adding water? Water has an SG of 1! Your beer does not, neither does whiskey.
__________________
ongreystreet is offline
 
Reply With Quote Quick reply to this message
Old 03-09-2011, 02:14 PM   #7
ongreystreet
Feedback Score: 0 reviews
Recipes 
 
Join Date: Nov 2010
Location: Columbia, MD
Posts: 313
Liked 6 Times on 6 Posts
Likes Given: 1

Default

If you beer is done, which it appears to be at 1.010. You can find the ABV of your beer by using (OG - FG) x 131.

When you add your whiskey you will change your gravity, but don't use that to calculate your ABV.

Let's say your brew is 5% ABV and you made 5 gallons.

Your brew has .25 gallons of alcohol if you were to separate it:

5 gallons * .05 = .25 gallons of alcohol

If you add 2 cups of 100 proof whiskey:

2 cups * .5 = 1 cup alcohol = .0625 gallons of alcohol

Now divide your total alcohol by total volume,

(.25 + .0625 gallons) / (5 gallons + .125 gallons) = .06 or 6.1% ABV

Think I got that right.

__________________
ongreystreet is offline
 
Reply With Quote Quick reply to this message
Old 03-10-2011, 12:37 PM   #8
AlanS
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jan 2011
Location: Harrisburg, PA
Posts: 25
Default

Quote:
Originally Posted by ongreystreet View Post
If you beer is done, which it appears to be at 1.010. You can find the ABV of your beer by using (OG - FG) x 131.

When you add your whiskey you will change your gravity, but don't use that to calculate your ABV.

Let's say your brew is 5% ABV and you made 5 gallons.

Your brew has .25 gallons of alcohol if you were to separate it:

5 gallons * .05 = .25 gallons of alcohol

If you add 2 cups of 100 proof whiskey:

2 cups * .5 = 1 cup alcohol = .0625 gallons of alcohol

Now divide your total alcohol by total volume,

(.25 + .0625 gallons) / (5 gallons + .125 gallons) = .06 or 6.1% ABV

Think I got that right.
Thanks. This is what I'm looking for.
__________________
AlanS 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
Prevent infection by adding alcohol Irena Beginners Beer Brewing Forum 1 12-02-2010 09:00 AM
Can spices throw off OG readings? SwampassJ Beginners Beer Brewing Forum 1 08-11-2010 04:53 PM
When adding spices for a wit, do you use a steel "tea" ball, or just throw them in? bgough Beginners Beer Brewing Forum 9 03-07-2009 02:35 PM
Adding alcohol question Grinder12000 Beginners Beer Brewing Forum 11 09-18-2008 12:00 AM
When to throw in the alcohol boost? PUD Beginners Beer Brewing Forum 4 04-06-2007 02:17 AM