Gravity reading before adding top off water

[milesbishop]

Hi, I am new to brewing and took a seminar on extract brewing. The instructor had suggested taking a reading before adding the top off water (8L). It was a 5 gallon batch and my reading was 1.067 and the target was anywhere from 1.040 - 1.050. Can anyone tell me what my true gravity should have been after adding the water? I know now this was not the best idea. I am brewing an Oatmeal Stout.

 

[duboman]

Not without a recipe:
Was the reading before or after the top off water, not clear from your question. It was probably recommended so you can calculate exactly how much top off water you would add to meet the expected gravity of the recipe after diluting with said water.

Keep in mind when brewing extract with top off water it is very difficult to get a complete mix of top off water and wort so most readings will either be slightly higher or lower depending on how well you can mix the two volumes.

Also keep in mind that when brewing extract your gravity will always be what the recipe states as long as you meet the exact final volume. This is because extract has a fixed gravity contribution. If the expected gravity was to be what you stated then that is what it should be. Your reading is most likely high because you got a poor mix and read the more dense wort versus a complete mix.

 

[jekeane]

You can do it with math. Unfortunately, I don't know the exact equation All you are doing though is taking the 1.067 @ 3g and diluting that with 1.000 at 2g (appx 8L) the calculator on my brewing software said 1.040.

This being said, as duboman mentioned, it takes some work to miss your gravity with an extract kit if you follow the directions.

 

[milesbishop]

Sorry for the confusing wording. Ill rephrase it..

I had a wort that was 3.96 US gallons. I did not add my 8L of water right away as the instructor said there would large amounts of blow off. I pitched my yeast and after 3 days, added my 8L of water. However, before pitching my yeast the wort had a reading of 1.067. I am simply just looking for an equation to determine what my actual OG is after adding my 8L of water.

 

[LLBeanJ]

~1.044

Edit: here's the equation...

(OG in points X Actual volume) / Planned Volume

(67 x 4.0 gal) / 6.0 gal = 44 gravity points = 1.044

 

[milesbishop]

OK cool, thats what other sources have told me as well. I will be sure not to do this next time around. Just curious as to what the equation is to get this gravity? Thanks.

 

[Mad4sax]

Use an online calculator:

http://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/

 

[chickypad]

The whole formula is simply G1 x V1 = G2 x V2 where G is gravity in pts and V is volume. You can use it to calculate the new gravity at the known new volume as above, or to calculate what new volume you need to hit your target gravity.