Adding up Gravity Numbers

[lostboysbrew]

We are at the tail end of turning our Double IPA into what you would consider a "Quad" IPA. Normally running 8.5%, we have pushed it all the way up into the high teens with multiple rounds of DME and sugar. A general question has come up however, how do you calculate an accurate ABV????

What we have done is measured our OG and FG at each addition. We have taken the difference in gravity each time, added it to our very first OG to get a true OG and then used the FG to calcualte the ABV. Any ideas if this is accurate???

Another thought was to Run the OG/FG numbers each time and add up the individual ABV% numbers. Open to any and all suggestions. According to our calculations we are rounding out just over 17% as of yesterday when 2.5lbs of sugar was added. See calcs below.

OG-1.094 (original)
FG-1.028
OG- 1.045 (added 3lb DME & Champagne Yeast)
FG-1.025
OG-1.052 (added 3lb DME and 2.5lbs sugar - High Grav Yeast)
FG-1.020
OG-1.038 (added 2.5lb sugar)
**ESTIMATED FG** 1.020
That makes the "True" OG 1.184 with a "FG" of 1.020 is approx 19.2%.


Is this the way to go about it?????

Thanks,

Lostboys

 

[smizak]

Just add up all of the gravity-point contributions of your extract and sugars and reformulate the recipe as if you added all extract at once. Then just use that number and your final gravity, as well as your final volume, to calculate your ABV.

 

[Driftless Brewer]

I would add up all the gravity points that were consumed (66+20+32+18=136) then multiply by 0.131 (136*0.131=17.82%). And you have a 17.82% beer. I believe the 0.131 is the correct conversion factor. . .

 

[a10t2]

Just add up all of the gravity-point contributions of your extract and sugars and reformulate the recipe as if you added all extract at once. Then just use that number and your final gravity, as well as your final volume, to calculate your ABV.

+1, no need to take a gravity reading every time. Either way, your OG/FG estimates readings look correct so far.

Also, the factor of 131 estimate for ABV is only accurate up to about 7%. More accurate formulas, and a JavaScript calculator, are here.

 

[lostboysbrew]

I would add up all the gravity points that were consumed (66+20+32+18=136) then multiply by 0.131 (136*0.131=17.82%). And you have a 17.82% beer. I believe the 0.131 is the correct conversion factor. . .

Is this a more accurate way of calculating ABV???

Would volume throw off calcuations. Obviously everytime we add we add liquid. We started with a 5 gallon batch and have rounded out just shy of 9 gallons.........how will this affect the number??

 

[lostboysbrew]

+1, no need to take a gravity reading every time. Either way, your OG/FG estimates readings look correct so far.

Also, the factor of 131 estimate for ABV is only accurate up to about 7%. More accurate formulas, and a JavaScript calculator, are here.

Could you explain how you get those numbers without taking a gravity reading everytime????

Would volume throw off calcuations. Obviously everytime we add we add liquid. We started with a 5 gallon batch and have rounded out just shy of 9 gallons.........how will this affect the number??

 

[smizak]

Take your total number of points. Divide by your final volume. That's your OG.

Subtract your OG by your FG, multiply by 131. That's your ABV.

More accurate is pointless, because the gravity point contributions are approximate. Does the extract really contribute 43 points per gallon or 43.4? Or 42.7? You'll get close enough.

Take a 5 gallon batch of beer with 6lbs of 43ppg extract used.

5 x 43= 258 gravity points
Divide by final volume in fermenter 258points /5 gallons = 51.6

I.E. 1.0516~1.052

If it finished at 1.012; 1.052-1.012=0.04

0.04x131 = 5.24% ABV

Divide your total points by your 9 gallon final volume to get your OG

 

[frazier]

Finally we get the data...

Would volume throw off calcuations. Obviously everytime we add we add liquid. We started with a 5 gallon batch and have rounded out just shy of 9 gallons.........how will this affect the number??

You started with 5 gallons at 1.094. This yields 470 gravity points. To this you have added roughly another 494 GP's (I'm going by memory here). Divide the total (964) by 9 gallons and you get 107.1, or a calculated SG of 1.107, and an ABV of 11.4%. While you added 11 pounds of sugars, you also added 4 gallons of water so the increase in gravity wasn't that much.

 

[weirdboy]

Yes volume changes the calculations. You cannot just add the numbers as stated here.


You really need to total the gravity x the volume for each contribution, then divide by the final volume.

EDIT: Frazier's explanation is pretty much what I was meaning to say.

 

[SumnerH]

Take your total number of points. Divide by your final volume. That's your OG.

Subtract your OG by your FG, multiply by 131. That's your ABV.

As mentioned above, (OG-FG)*131 isn't a great estimate for big beers--it's off by nearly 4% ABV on a beer this big.

The more accurate formula is:
ABW = 76.08*(OG-FG)/(1.775-OG)
ABV = ABW*(FG/.794)

Here:
OG= 1.156
FG = 1.020

Using the (OG-FG)*131 estimate gives (.136)*131 = 17.816% ABV

Using the actual calculation:
ABW = 76.08*(1.156-1.020)/(1.775-1.156) = 16.72%
ABV = 16.72*(1.020/.794) = 21.47%

21.47% ABV!!

But that's ignoring the volume increase--you actually need to go back and recalculate the nominal OG of each step based on the final volume.

For instance, if you did:
1. 5 gallons @ 1.100 OG
FG: 1.020
2. added 1 gallon of sugar+water and had
6 gallons @1.050 OG
FG: 1.020
3. added 1 gallon of sugar+water and had
7gallons @1.050 OG
FG: 1.020

You'd have:
1. 80 gravity points in 5 gallons consumed * 5/7 = 57.1 points consumed in 7 gallons
2. 30 gravity points in 6 gallons consumed * 6/7 = 25.7 points consumed in 7 gallons
3. 30 gravity ponits in the final 7 gallons

for a total of 57.1 + 25.7 + 30 = 112.8 points consumed. With an FG of 1.020, that gives you a nominal 1.132 OG to use with the 1.020FG in figuring out ABV.

 

[lostboysbrew]

As mentioned above, (OG-FG)*131 isn't a great estimate for big beers--it's off by nearly 4% ABV on a beer this big.

The more accurate formula is:
ABW = 76.08*(OG-FG)/(1.775-OG)
ABV = ABW*(FG/.794)

Here:
OG= 1.156
FG = 1.020

Using the (OG-FG)*131 estimate gives (.136)*131 = 17.816% ABV

Using the actual calculation:
ABW = 76.08*(1.156-1.020)/(1.775-1.156) = 16.72%
ABV = 16.72*(1.020/.794) = 21.47%

21.47% ABV!!

But that's ignoring the volume increase--you actually need to go back and recalculate the nominal OG of each step based on the final volume.

For instance, if you did:
1. 5 gallons @ 1.100 OG
FG: 1.020
2. added 1 gallon of sugar+water and had
6 gallons @1.050 OG
FG: 1.020
3. added 1 gallon of sugar+water and had
7gallons @1.050 OG
FG: 1.020

You'd have:
1. 80 gravity points in 5 gallons consumed * 5/7 = 57.1 points consumed in 7 gallons
2. 30 gravity points in 6 gallons consumed * 6/7 = 25.7 points consumed in 7 gallons
3. 30 gravity ponits in the final 7 gallons

for a total of 57.1 + 25.7 + 30 = 112.8 points consumed. With an FG of 1.020, that gives you a nominal 1.132 OG to use with the 1.020FG in figuring out ABV.

We measured the total gravity everytime we added.

5 gallons @ 1.094 --> 1.028

6 gallons @ 1.045 --> 1.025

7.5 gallons @ 1.052---> 1.020

8.5 gallons @ 1.038 ---> TBD


So that being said, you can't use just the total of the numbers???

 

[frazier]

So that being said, you can't use just the total of the numbers???

Some numbers you can total. Some you can't.

Add the total gravity points. This will be the total sugars, in pounds, times the GP contributions of each different sugar in GP's per pound. From your data, this equals 964 gravity points.

Add up the total gallons. Here you call it 8.5 gallons.

964 / 8.5 = 113 gravity points per gallon. So for calculation puposes, your O.G. is 1.113. When you can measure your F.G., you can get the ABV.

There may be other ways to get the answer, that are more complicated. "Complicated" means "error-prone". If they give a different answer, they are wrong.

 

[weirdboy]

As an aside, I expect your "Quad IPA" isn't going to taste much like an IPA anymore if you hopped it appropriately for the original 1.094 and then added that much sugar to it.

 

[frazier]

As an aside, I expect your "Quad IPA" isn't going to taste much like an IPA anymore if you hopped it appropriately for the original 1.094 and then added that much sugar to it.

He didn't really add that much sugar to it. He raised the effective OG from 1.094 to 1.113. Since his additions were probably unhopped, he's lowered the IBUs by going from 5 gallons to 8.5 gallons. So yeah, who knows how it will turn out. Let us know!

 

[lostboysbrew]

Thanks so much for all the info. But we did however over hop our 5gals recipe. So as of right not it still tastes the same. Here are our ideas in ways to bring the ABV up. We are going to throw another 5lb of sugar at it. However we are going to start with 2gals of water and boil and add sugar and then boil down to 1gal or under. The other idea is to take 2-3 gals our of the batch right now and freeze it. then take off the ice crystals and add it back to the original once we bring it back to room temp. How do people feel about these ideas?

 

[weirdboy]

Well how far along are you on gravity so far? I mean I think you might be getting close to the yeast pooping out and you want to be careful about the sugar additions at this point. Once the yeast poops out you are just adding pure sweetener to the beer that won't ferment out.

What I would do if I were you is take some smaller samples and do quick ferment tests with various concentrations of sugar solutions to see how much more the yeast can tolerate. Don't forget to leave one or two of the samples alone and ferment alongside for your control.

 

[lostboysbrew]

Well how far along are you on gravity so far? I mean I think you might be getting close to the yeast pooping out and you want to be careful about the sugar additions at this point. Once the yeast poops out you are just adding pure sweetener to the beer that won't ferment out.

We have used a champagne yeast as well as a high gravity yeast so the yeast should be ok for a little while.........

I know the GP for DME and LME, where do you get GP's for other ingredients such as the grains and straight sugar???

 

[smizak]

The ppg for white table sugar is 46.