adding 1 g to 5 g recipe - keep OG the same

Question

So i've got a 5 gallon partial mash kit(OG 1.065), and I am looking to add around a gallon to increase my yield for the session.

What formula could I use to know how much extra dme to use to keep gravity constant while adding a gallon?

I already have a formula to find the end gravity when just increasing volume (BG*BV=EG*EV), but how do I factor in a volume increase that will have a gravity higher than water???

Answer 1

You want the fraction that you add to have the same OG as the rest of the batch. In your case its one, its simple, you want one gallon at 1.065. I see DME is 45 points per gallon per pound, so :

65 = 45 * X (where X = pounds of DME).

X = 65/45 = 1.44 lbs of DME

In general terms, the formula would be

(OG /Points ) * V (where v = volume to be added in gallons)