How much is lost during the boil?

[paulgough]

I'm trying to calculate how much liquor I will need for my next brew.

Last time I think I got my pre boil volume wrong.

How much should you allow for evaporation during the boil?

If I'm making 23 litres of beer and boiling for 90 minutes, what should my pre boil volume be?

 

[PD]

its a guestimate until you do one and take measurements. Its also very dependant and variable on the ambient air temps and climatic conditions.
It also depends on how vigorous you boil.
around 9% was the figure given when I started reading about it. However from my brewings I've found this way under estimated and I work around 15% loss and still get it wrong.
Vossey recently gave me a calculation and I intend to put it to use when I get my new equipment and boiler...

Assuming a 1 hour boil..

100/(your brew length x amount after boil)-100

therefore if your brew starts with 26 litres and ends with 19 litres the boil off % =

100/ 26x19= 73.1% left therefore your boil off % = 100-73.1 = 26.9% boil loss.

Hope that helps

 

[The Goatreich]

I've never worked it out properly for my equipment, but in general if I want a 23l brew length I need at least 30l pre boil.

 

[Hawks]

As said it will vary depending on the boil, pot shape / size etc and you'll get to know it

I work on about 20% :thumb:

 

[Aleman]

For a nominal 3KW '25L' boiler you can estimate around 20-25% loss to evaporation during a 90 minute boil . . . which is way to high to be considered best practice where ideally you are looking for around 10-12% . . . . Still it won't stop you making great beer, but reducing the thermal loading of the wort is a good idea if you can do it.