Partial Mash Math Question

We've had our equipment for two weeks and have brewed twice. Needless to say, I think we're hooked.

Today we tried our first partial mash and I have a question about efficiency and reverse engineering the extract needs to hit our OG target.

We took a hydrometer reading, calculated our efficiency, and through a bunch of other random calculations, backed into what we needed. Is there a formula where you can take the hydrometer reading, subtract the difference from your goal, and then figure out exactly how much to add based on points needed?

I'm sure my next question will be about our mash itself and getting better efficiency.

Thanks for the help!

Stay with me...

So, if you do your partial mash and end up with 6 gallons of 1.031 wort (for example) and you want a pre-boil target of, say, 1.049 wort, you need 18 more points (1.049 desired minus 1.031 current).

Next, you need to know your extract. DME is typically 44 - 46 ppg (points per pound per gallon) and LME is typically 35 - 37 ppg. Your supplier should be able to get you this info.

So, let's assume you are using LME at 35 ppg. For each lbs. of LME you add to a 6 gallon batch, you will raise the overall gravity by 5.8333 points (35 ppg / 6 gallons wort). Hopefully that makes sense so far.

So, now take the 18 points you are trying to make up (1.049 - 1.031) and divide those 18 points by the 5.8333 points (from each 1 lbs. LME). 18 / 5.8333 = 3.0857 lbs of LME you will need to add to your 6 gallons of wort to reach 1.049.

Got it? Simple, right? lol.

The equation would be:

Also, just found this in another thread:

http://www.ahomebrewlog.com/gravity_adjustment/