Specific Gravity Formula?

[beersteiner2345]

OK, so I just finished brewing and measured my OG at 1.064 when there was 5 gallons in the fermenter. Is there a way to determine what the OG would be if I were to add 1/3 gallon of water?

I was shooting for an OG of 1.058... about how much water would I add to adjust to this from 1.064 at 5 gallons?

 

[Revvy]

Do you have beersmith? It has a dillution calculator.

 

[beersteiner2345]

I have beersmith... will check it out.

Used this instead in the mean time.

http://www.brewheads.com/newsg.php

1/3 gallon (the amount of bottle water I currently have) will bring me to 1.060, which is close enough that I can't justify going to buy more water.

 

[Revvy]

Cool to know there's an online one if I'm not near my beersmith.

 

[imrook]

You can do dilution calculations pretty quickly by hand. To obtain an S.G., you divide your _total_ number of points by the _total_ number of gallons, divide by 1000 and add 1. To calculate points from an S.G. subtract the one, multiply by 1000, then multiply by the number of gallons.

To solve your dilution question, we first figure out how many points are in your beer:
(1.064 - 1) *1000 = 64
64 * 5 = 320 points

If you dilute this down to 5.34 gallons, you'll have an S.G. of:
320 / 5.34 = 59.99
(59.99 * 1000) + 1 = 1.05999 or 1.060

If you want to hit 1.058, solve the equation

1.058 = ((320 / x ) * 1000) + 1
.058 = (320 / x) * 1000
58 = (320 / x)
58 x = 320
x = 5.517

So a little over 5.5 gallons of water. Who needs beersmith?

 

[beersteiner2345]

The nerdy part of me is happy you posted this, as I was trying to do it by hand at first.

My old chemistry and physical science did not come back to me very quickly though. lol

 

[Ohio-Ed]

My first question would be, how did you boil? Also, was this all grain or extract?
If you did a full boil, you are probably OK.
If you did a partial boil and added "top up" water, I would not trust your OG reading... It is VERY difficult to mix it well enough to get a good sample.

Ed

 

[Ogri]

You can do dilution calculations pretty quickly by hand.

Thanks for posting that. Rather impressive and, definitely, a handy formula.

 

[beersteiner2345]

My first question would be, how did you boil? Also, was this all grain or extract?
If you did a full boil, you are probably OK.
If you did a partial boil and added "top up" water, I would not trust your OG reading... It is VERY difficult to mix it well enough to get a good sample.

Ed

Partial boil extract. I can promise you 100% it was mixed evenly... (I am actually quite anal retentive about aeration after several stalled fermentations. My process for aeration is also highly effective at mixing it up real well.)

I always boil 3 gallons. Then add 2.5-3 gallons of 32.000001 ( ) degree water depending on how much boil off I had, then put the immersion cooler in and stir hard for the 10-15 minutes it takes to cool it to 80-82 degrees. Then I autosiphon from the boil kettle into the fermenting bucket, allowing the wort to fall about 4-5 feet from the end of the siphon to the bucket below, all the while moving it around to aerate the wort.

So I am pretty sure it was mixed well.

O.C.D. sucks.