Boil Off Volume Issue

[Skonto]

I recently got a new kettle to boil in.
Previously I did 1 gallon mash and 1 gallon sparge, and the after the 60 minute boil I was down to a gallon in volume (actually a bit less as I usually had to top the carboy off with water).

My new kettle I'm doing similar mash, sparge, and boil process, but the amount of boil off is considerably reduced. Last time it took me almost 90 minutes to get to the 1 gallon size.
I understand that the longer I boil it, one impact is that my hop addings will change in IBU value. So my question is:

Should I reduce the size of my sparge so there is less total liquid to boil?
Or should I keep my boil size the same, boil for longer and just adjust my hop timings to match the ibu scheduling?
Any other options I should be considering?

Thanks in advance!

 

[botigol]

I would reduce the sparge, because the increased boil time introduces the possibility of caramelization that you may not want.

 

[bruce_the_loon]

Extend the boil and delay the hop timings so that they are in the boil for the same time as before. Hop timings are given as time in the boil, not time to add, so a 60 minute addition will be at the start of a 60 minute boil or 30 minutes into a 90 minute boil and will give the same IBUs.

Adjusting mash and sparge volumes might adversely affect the efficiency and sugar extraction and conversion, so leaving those volumes the same and lengthening the boil to 90 minutes should lead to much the same wort as the 60 minute boil in the old kettle made.

 

[kh54s10]

You really need to determine the boil off rate, then collect the amount of wort for the preboil so that you end up with the right amount when the boil is done. If you do a 60 minute boil you will need x amount of wort with hops adjusted for the IBU that you desire. If you do a 90 minute boil, sometimes desired for pilsner malts, you will need y amount of wort, and a different amount of hop, or adjusted addition timing to get the IBU that you desire.

So in general, yes sparge less so that you reach the proper amount at the end of the boil.

 

[bruce_the_loon]

And now you have two conflicting answers and the only way forward is to brew two otherwise identical batches to see what produces the better beer.

Or you could go with the chap with 11000 posts versus the one with 27.

 

[Skonto]

Well I'm glad to hear I have options, but I'll probably reduce my sparge amounts as I dunk sparge BIAB and there always seems like there is more water in this part of the process than required.

Thanks for the input everyone.