I was just experimenting with the 'Brew It!' tool on Brewers' Friend and the instructions say that for a 12 litre boil, I should add 8.8 litres to the kettle along with 5kg of dry malt extract which equates to a further 3.2 litres totaling 12L - my target volume.

I'm going to reasonably assume that Brewers' Friend knows it's stuff but I have always taken the boil volume to be the water only!

Have I been doing it wrong?

For the purposes of future brewing and consistency should I just adjust my recipe so the pre boil water volume reads 12L?

  • Is 12 liters the volume you want in your kettle after mashing or the volume you want in your fermenter? Jul 15, 2015 at 12:59
  • 24l is my desired fermentation volume. The 12L I specified was 12L of water to bring to the boil then add 3.2L of malt, totaling 15.2L. I would then top up the wort with another 9 or so litres to reach my target of 24L
    – Phizzy
    Jul 15, 2015 at 13:10

1 Answer 1


It it dry or liquid malt extract? Dry malt extract will dissolve into the water, leading to a minimal volume change, whereas liquid malt extract still has a substantial portion of water, and will have somewhat like the volume change you describe, though I don't believe it's quite 1:1.

In short, your boil volume should be the boil volume. With dry extract, that does not include the negligable "volume" of the extract. With liquid extract, that will include some portion of the volume of the extract.

  • I am using dry malt extract only. I was working on the malt powder displacing an amount of water equal to its volume... You said it dissolves which I guess makes sense. It has what, 3% moisture content? So if I leave a bit of room in my boil pot to allow for a small increase in volume + hot break etc. I should be fine? Thanks!!
    – Phizzy
    Jul 15, 2015 at 14:42
  • Ideally your boil kettle would be 50% larger than your pre-boil volume, mostly to account for boil-over. The volume difference from thermal expansion of the water/wort is minimal but non-trivial, but the boiling head and boil-over is the bigger concern by far. I regularly have a 12gl pre-boil volume in my 15.5gl keggle, and I watch it like a hawk as it comes to a boil to prevent boil-over.
    – jsled
    Jul 15, 2015 at 18:19
  • Hi Jsled, as an update to this - I brewed last night and the DME ended up taking up approx. 1L per kg in the pan. I had to split the boil up into 2 pans as not to compromise on my boil size. As this goes against your answer, 1) Should I post this as another answer? 2) I don't doubt your own answer/experience, possibly our DME was of a different brand/type?
    – Phizzy
    Jul 17, 2015 at 14:17
  • You should doubt my answer, with direct evidence to the contrary in front of you! :)
    – jsled
    Jul 17, 2015 at 14:46
  • 1
    I won't trust you again in the future then! ;) Thanks again!
    – Phizzy
    Jul 17, 2015 at 15:08

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