Batch sparging questions

[The Goatreich]

I'm opting for batch sparging for my first brew day on Saturday as it's supposed to be easier, however I'm not entirely sure how the calculator works.

If I have the results as follows:
Total volume of water: 29.4 L
Calculated wort volume: 23.3 L
Batch Volume: 11.7 L
Water required for batch #1 17.7 L
Mash Volume: 12.5 L
Top up Volume: 5.2 L
Water required for batch #2: 11.7 L

Do I use 17.7L for the initial mash, then after 60 minutes (or whatever the recipe calls for) add 5.2 L at sparge temperature, collect first runnings, then drain out?
Then for the second batch do I add a second 11.7L of sparge temperature water, stir and leave for 20 minutes, collect first runnings then drain again into the same vessel as the first batch was in?

Do I need to stop the second sparge when the gravity gets to a certain level, or has the calculator just negated that step, meaning that the amount of water should give me the required gravity?

As far as the quantities go, how accurate to people do this? I'm planning to calibrate my HLT/boiler by filling and marking it up 1 litre at a time, but that will be hard to judge the tenths of a litre required for the calculated quantities. Presumably people use a measuring jug to fine tune the amount?

 

[Pinck]

You got it. Mash wiith the 17.7L. After 60 minutes add 5.2L, stir and drain. Then add 11.7L, stir and drain.

Being your first time batch sparging, I'd recommend measuring your output from your first runnings. You're going to have some dead space in your mash tun that I'm not sure if your calculator is taking into account. If your first runnings are short at all, you now know that you need to add that much to your top up for next time.

I just measure with a 4L measuring cup. Certainly not scientific accurate, but I do my best with what I've got :thumb:

 

[The Goatreich]

Great stuff cheers. The calculator does account for deadspace, but I'll measure the gravity as I go aswell.

 

[oz11]

If I have the results as follows:
Total volume of water: 29.4 L
Calculated wort volume: 23.3 L
Batch Volume: 11.7 L
Water required for batch #1 17.7 L
Mash Volume: 12.5 L
Top up Volume: 5.2 L
Water required for batch #2: 11.7 L

The way I read that is the total volume of water required is 29.4L. Which is equal to 12.5L + 5.2L + 11.7L.

So you use 12.5L for the initial mash, top up with 5.2L for the first batch, then use the remaining 11.7L for batch #2.

Hope that helps.

 

[oz11]

You got it. Mash wiith the 17.7L. After 60 minutes add 5.2L, stir and drain. Then add 11.7L, stir and drain.

:nono:

This would give you 17.7L + 5.2L + 11.7L = 34.6L of water required.

 

[The Goatreich]

Aaah yes I see, that's actually really bloomin obvious now . What's the reasoning behind the topping up and not putting all the 17.7L in the first batch?

 

[Pinck]

... What's the reasoning behind the topping up and not putting all the 17.7L in the first batch?

Fancy science/math stuff that tells us the greatest extraction comes from equal batch sizes.

Fancy math can be found here: http://hbd.org/cascade/dennybrew/ under "Formulae and definition of variables"

 

[The Goatreich]

Great stuff, thanks.