Adjusting your volume for boil off

[Graeme]

I have been curious about this since I started brewing bigger batches and using a new boiler which has a substantially higher boil off rate than my previous one. Is there anything you need to be careful about when adjusting your pre boil volume to account for boil off? Particularly in the case of long boil times. For example, if I want to brew a 30 litre batch over 120 minutes and I know that on my set up I will loose about 10 litres over the two hours is it really just as simple as sparging to a pre boil volume of 40 litres? I'm concerned that gravity might be compromised somewhere here. Maybe I'm wrong.

Thanks in advance! Still very much finding my feet with all grain!

Graeme

[micromaniac]

dont over sparge just top up the boiler as you go along with pre treated water...i do 46ltr 2 x23ltr at a time and i pre treat about 75ltr and usualy have a small amount over

[Graeme]

dont over sparge just top up the boiler as you go along with pre treated water...i do 46ltr 2 x23ltr at a time and i pre treat about 75ltr and usualy have a small amount over

I'd imagine that gets a bit tricky? Also, hop utilisation would be difficult to calculate if you are topping up during the boil. Can you tell me the issues with over sparging? I would have thought if you know you're general brew house efficiency and your boil off then you should be there or there abouts your gravity. As I said in my opening post though, I could be wrong!

[Wolfy]

Boil off rates of between 5 and 15% per hour are generally considered typical, with somewhere about 10-12% a good average.
While you are on the higher end of things, the figures suggested above indicate that you are still within the recommended range.

I don't know how you are planning your brewing but most brewing software will take the boil-off into account and allow you to correctly determine the water and grain required for your target gravity.
But yes the basic theory is that you'd sparge 40L boil off 10 to leave 30L into the fermentor.

[orlando]

dont over sparge just top up the boiler as you go along with pre treated water...i do 46ltr 2 x23ltr at a time and i pre treat about 75ltr and usualy have a small amount over

I'd imagine that gets a bit tricky? Also, hop utilisation would be difficult to calculate if you are topping up during the boil. Can you tell me the issues with over sparging? I would have thought if you know you're general brew house efficiency and your boil off then you should be there or there abouts your gravity. As I said in my opening post though, I could be wrong!

The issue with "over sparging" is one that regularly comes up but is of less or no concern if your mash pH stays below 6. Treat sparge liquour to ensure a lower pH and there is no problem with over sparging, above 6 and you run the risk of tannin extraction. I keep reading you shouldn't sparge below 1.010 but so far have seen nothing but anecdotal evidence for it; pH is the key.

[Graeme]

Thanks for your input guys, it's very helpful. I did read one or two threads regarding PH and 'over sparging'. I use PH 5.2 mash stabiliser in my mash but haven't ever used it with my sparge water. Would this be a way of 'treating' the sparge water to avoid the PH rising?

[orlando]

Try it and report back.

[paulg]

using alemans batch sparge software it tells me to collect 48.2 litre wort for my recipe as my boiler is only 40 litre as the boil continues you can top up as evaporation happens
my question is what is the minimum boiltime that the last top up added must have before flame out
also if my mash tun is too small to batch sparge with 2 batches I assume I can sparge 3 batches(software says mash tun of at least 45.9 litres required)
10 kilo grain +25 litres liquor =35 myy tun is 38
loss to grain =10 leaves 15 litres
drain add 1/2 of 33.2 (48.2-15) =16.6 leave 15 mins drain
add 16.6 wait etc =total 48.2 does this work