Changing pre-boil gravity

[Cadbury]

G'day men,
I have been told that I can adjust my pre-boil gravity by adding either malt or water. If my target pre-boil gravity is 1.039 and the actual pre-boil gravity is lets say 1.050, what do I do? If I have to add one or the other, how much would be needed to bring it down to 1.039 in a 30L batch?
Many thanks
Cadbury

[warra48]

What's wrong with 1.050 ???

Anyway, it's a simple equation.

For example, say you have 30 litres @ 1.050.
You want to get it down to 1.039.
Thus 30 x 50 = 1500 ÷ 39 = 38.5 litres.
Therefore, add 8.5 litres of water.

Remember, if you increase the volume of your beer, you'll need to adjust your hopping schedule to allow for the changed volume and gravity.

[Cadbury]

Thanks,
So if the measurements were the other way, I would do the same calculation and add some malt. So if I wanted 1.050 and got 1.039 I would just reverse that formula and add the amount of malt needed. Have I got that right?
Cadbury

[warra48]

Yep, that's how it works.