Pre-boil water levels

I thought that I used 8gal on a 10lb grain bill thelast two times, and had ended up with 5.5 gal of wort

This time on a 11lb bill I was left with 6.25 gal of wort.

How does this happen?

Is it better to use less water and add more if it boils down under 5 gal?

I assume you're talking about pre-boil volumes here. It took me several batches to get my water and wort volumes under control and develop calibration numbers for my system so that I could hit my targets fairly accurately. Grain absorbs water. More grain = more absorption. The only conclusion I can draw is that you weren't using 8gal before.

A quick check here shows that using 8 gallons of mash/sparge water on 11 lbs of grain should yield 6.25 gallons of wort. So you're latest batch appears to be spot-on. My guess is that you either weren't measuring your water volumes correctly before, or you were leaving a bunch of wort in the mash tun. Every batch you get better

Thanks. Seems I should be using about 7.25gal pre boil most often

ThePonchoKid said:

Thanks. Seems I should be using about 7.25gal pre boil most often

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You need to take good notes throughout the process and try to maintain the same vigor of boil.

Things that contribute to loss:
Grain absorption-will vary based on size of bill
Tun dead space
Kettle loss, unless you are a dumper of everything
Shrinkage, cooling and boil off

Factor all these things and add them to your sparge volume and you should be able to hit your volumes

I have to agree with duboman. I've done multiple batches of the same recipe but the second time I brewed it, even through I kept the boil at the same rate and the amount of water/grains the same, I still ended up with a lot less liquid at the end merely because of the ambient temperature. Granted, it was quite an extreme difference, the first time I did this recipe it was 15 degrees outside and the next time it was 70--as I get to brew in an unheated shed, but it was something I had not taken into consideration the second time around until it was too late. Not to be off topic, but I do love winter brewing though as cooling the wort doesn't get much faster when you can stick the hot pot into a snowbank.