Batch sparge volume question

[Brewers Whoop]

Having a bit of a Homer moment here.

Trying to calculate the voulme of liquor I need to prepare for my first A.G brew (B&T Shefford bitter, from G.W's book).

On the 'batch sparge and boil volume calculator' available from here, the final four boxes after all the data has been added and 'calculate' presssed are:

Total quantity of water required for batch #1:

Mash volume:

Top up with:

Water required for batch #2:

My questions are these: what is the last box? Is that for someone wanting to make a second brew from the same grain?

If so, presumably the two key boxes for someone wishing only to brew a single batch would be the 'mash volume' box and the 'top up with' box - the latter being the volume required to batch sparge?

Or am I barking up the wrong tree entirely?

[dave-o]

I'm not sure this answers your question entirely, but for what it's worth i go 13-7-13 for a 23l batch with 4-5kgs of grain.

That's:

13l: Mash
7l: Mash-out water
13l: Sparge water

But of course it depends what your equipment is.

[vacant]

A Wort Required for the Boil:
B Made up from two equal quantities of:
C Total Quantity of Water Required For Batch #1:
D Mash Volume:
E Top Up With:
F Water Required for Batch #2:

You want to start your boil with (A) litres. The calculator assumes you will drain your mash tun twice, getting (B) litres each time.

So... you will pour (D) litres into your mash tun and dough in the grain. After 90 minutes you will then add (E) litres. When you drain, some of the liquor remains soaked in the grain and trapped in the dead space of the mash tun so you can't drain it all out (you don't get (C) out, C = D + E). You only get one measure of (B) out.

As your grain is now soaked and there is liquor in the dead space, when you add a further (F) litres, you'll drain (F) out into your boiler.

[Brewers Whoop]

Sound of penny finally dropping. Thanks guys - and particularly for that explanation, Vacant.