Pre boil and batch size confirmation - Really dumb question

[Hardman1982]

Hi Learned folk.

Quick question I'm a BIAB with mixed results at the moment.

For Brewers friend it has estimated boil size, then batch size.

I've taken this to mean what I start with pre boil, that batch size is after I top it up with water?

Boiling with 17 litres of wort at the moment, than 12 litres normally makes it into the fermentor than normally top up to 18 litres or so depending on the refractometer.

Thanks folk.

 

[jeffpn]

My boil size for BIAB is 7.25 gallons. My batch size is 6.5 gallons. That’s because I lose 0.75 gallons of water due to boil off during the hour. I hope that helps.

 

[J A]

You have the concept right. Topping up is not uncommon when doing small batches but adding back 30% of your volume is unusual when brewing all-grain.
I'm curious why your pre-boil volume is lower than your desired batch size. Pot too small? There are ways around that but getting a bigger pot should be your most immediate goal.