Why is boil volume so important?

[Bomber Rock]

Evening all.

Tranferred my first all grain BIAB this weekend (G&G Pacific Ale AG kit). Tasted really nice, better than any of my previous excract efforts. Can't wait till it's carbonated.

Can you help clear up some of my confusion before I start my next brew session?

I notice on all the brewing apps/excel sheets, in youtube vids and in conversation here, everyone seems to be concerned with this starting volume of their boil, with the aim being having the right volume of wort to transfer from the kettle and to the fermenter.

With my last brew, I aimed to have, at the end of my boil, slightly less wort than the volume of my no chill cube. Instead of squeezing, I just topped up with freshly boiled water from my kitchen kettle. My cube is about 17L.

Then, I transferred to the fermenter, and topped up to fermenting volume (21L) with tap water in a sanitised jug.

Am I missing something here? Am I doing something wrong?

 

[manticle]

Nothing wrong as long as you know you are essentially diluting everything - colour, gravity, ibu, melanoiden level, etc.

Also getting desired volume (be it concentrated to dilute or the 'right' amount for cube) helps iron out deficiencies in process/equipment.

Note that you are still aiming for a desired final volume and gravity.

 

[Danscraftbeer]

No. (to opening post)
Its the end result that you have to refine. No matter how you wrangle the boil volumes.
I boil at least 90 minutes because of limited capacities.
It gets better efficiency. More sparge larger pre boil volume more boil off.
Ranging brew house efficiency 72% to 85%.
Other thoughts to consider. Award winning brewers getting far lower efficiency rates just using more malts and less extract. Less extract/ efficiency you avoid tannin's I would presume.

 

[Lyrebird_Cycles]

You actually get more polyphenol (tannin) extraction if your efficiency is low, because you have a larger amount of polyphenol containing material exposed to the same temperature profile. The polyphenols are contained primarily in the husks which are thin so they will extract more efficiently than the large remnant grist particles which are the primary cause of poor (<95%) efficiency. This is one of the reasons I am always chasing efficicency improvements.

To the OP: boil volume affects things like AA extraction efficiency since the net rate of extraction reduces as boil gravity increases. If you are follwing a recipe, it is well to try to get the boil volume right.

 

[Bomber Rock]

Thanks. I'm still a little confused, but I'm reading from you guys that my method isn't ideal, but not the end of the world.

I'll look to get a bigger no chill cube that can accommodate the full 21L (or so) volume.

 

[mattyh77]

I use the blue bunnings 20l jerry and it fits 23l in it. The wort seems to expand the container bit. I still have to give it a little squeeze to get the air out.