My beersmith brew sheet printout gives me some gravity numbers that I can't make head or tail of:

How BeerSmith 2 calculates the gravity

How can the pre-boil gravity (when I haven't added 57% of the malt yet) be 1,084, while the post-boil gravity is only 1,048? Has it added the top-up water to the bottom calculation, or something?


I've now brewed this beer. The measured pre-boil gravity was 1.023. I did not remember to measure the post-boil gravity, but after adding 10 l of water and 1,8 l of starter, the measured OG was 1.046 and the batch volume was 22,5 l.

  • Go to the beersmith2 water volumes area for that recipe and check for top-up water.
    – Dale
    Aug 26, 2012 at 20:44
  • Top Up Water under Fermentation/Bottling is set to 10 l -- it's a partial mash. But of course that water isn't added until after cooling the wort. Aug 26, 2012 at 21:15

1 Answer 1


I just created a test recipe and when I add top-up water in the fermentation/bottling section, the water volume in the mash section decreases, the pre-boil gravity increases, and the estimated OG stays the same.

What this tells me is that the 1.048 in your example is after the top-up water is added. In some places in the application, the 1.048 value is just called "Estimated Original Gravity". In your screen shot, it's got "post boil" in the description, which is confusing, but I think it's accurate. It's just post boil and post top-up water.

  • 1
    What about the 4x too high pre-boil gravity estimate? I sincerely doubt my mash efficiency is 0%, even with BIAB, but that's what BeerSmith tells me. Aug 27, 2012 at 8:35

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