Newbie question about volume

Hey guys
I'm gonna make the jump into all grain brewing. I got myself the "Beer Alchemy" app and trying to put numbers in... It's wanting the "pre boil" and "post boil" volumes... I know theres obviously going to be evaporation... but at what rate, i haven't got a clue???
I have 6gal fermenters, and I want to end up with a full 5gal keg (after siphoning off the good stuff)

What should my pre-boil volume be for a 60min boil? and what about a 90min boil?

I have a 10gal brew pot so i'm guessing this should be big enough to end up with a full 5gal of finish beer either way... right?

You'll have to figure out your own personal boil-off rate. Boil 5 gallons of water for an hour, and re-measure. It can range, I believe mine to be in the 1-1.5 gallon range. Depends on how rolling your boil is.

As far as cooling, I think its a 4% shrink on volume? Someone else may chime in here to correct me.

Thanks Schecter

I've just come up with a new question.... The recipe i'm using calls for 6% brown sugar, sounds to me like it should be a fairly common fermentable.... but it's not listed in "Beer Alchemy"????

Hey but they do list "Demerara".... whatever the hell that is!!

Schecter said:

As far as cooling, I think its a 4% shrink on volume? Someone else may chime in here to correct me.

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This is correct, but during heating, the wort expands by about 4%, so you'll end up with the same amount. Boil-off rate needs to be taken into account, but not this.

ThunderpantsBrewing said:

This is correct, but during heating, the wort expands by about 4%, so you'll end up with the same amount. Boil-off rate needs to be taken into account, but not this.

Click to expand...

I see what you mean, but I input only to say don't aim to finish a boil with 5.0 gallons. Aim for, what, 5.2?

Stef, I don't use Beer Alchemy, but there may be a way to input new ingredients if it truly isn't listed anywhere.

Demerara is a partially refined sugar, it is not brown sugar. If you're simply looking for an O.G. to aim for, it may be suitable as a temporary replacement. Never used it, though.

Schecter said:

I see what you mean, but I input only to say don't aim to finish a boil with 5.0 gallons. Aim for, what, 5.2?

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Yes, 5.2 finished boil volume would yield 5.0 after cooling, but for the OP: you have to watch some of these brewing softwares when calculating volume. Some of them don't make a distinction between finished boil volume and cooled wort volume, so you'll have to make that adjustment yourself.

A bit of trial and error will come into play as you figure out your system. My pre-boil is about 26-27l to get 20l in the fermenter with a 90 min boil).
I also use 30l (6gal) fermenter but only have a 30l boil kettle and run a stupidly fine line with boil overs.