preboil vs postboil gravity

General Homebrew Discussion
1

Had a preboil volume of 6.5 gallons and 1.042 gravity. Postboil gravity was 1.047 which means I should have had a post boil volume of 5.8 gallons correct? My post boil volume looks closer to 5.4 gallons and I doubt I lost 0.4 gallons when transferring from the kettle to the fermenter.

I made one small change to my process and my preboil efficiency was 75%. From my postboil measurements, my efficiency appears to be 70% which is about what I average. I don’t know if the small change I made may have increased the efficiency or not.

Any thoughts? Should I just use my preboil gravity to calculate my efficiency?

2

If you want to know your mash efficiency, use the preboil gravity.  If you want to know your brewhouse efficiency, use post boil into the fermenter.

3

Okay. I suppose I should be tracking my mash efficiency instead of my brewhouse efficiency which is what I have been doing.

4

I only track brew house, IMO easier. I’d track mash efficiency if I was worrying about keeping a CFO happy, or if my mash efficiency was too high. All I care about is close repeatability. I also don’t have 11 pallets of cans with an ABV printed and TTB looking over my shoulder

5

Mash efficiency is helpful in deciding things like adjusting crush, comparing grains for a particular recipe and the like.  Brewhouse efficiency for me is less important between the two, but mine is typically in the low 70’s, which I accept given my system.  YMMV, of course.

6

Brewhouse efficiency is a bit easier, but with the amount of hops I use, preboil is my best gauge for measuring consistency. Plus, I’d prefer to know if I’m going to need to adjust my gravity as early on in the process as possible.

7

You can use this to figure out your efficiency.

Beer Smith uses Brewhouse in the eff field.

Also to figure out how much you boiled/changed gravity use this:

Hope that helps. I use these all the time

8

I use brewers friend too. Works great for me since I’m android only. Very handy

9

+1.  I measure preboil so I can adjust if need be as well.

10

Thanks everyone. I use Beersmith for approximating volumes, gravities, etc.

I guess I am just baffled at how my post boil volumes are extremely inconsistent. That is what makes it hard to use brewhouse efficiency. If my post boil volumes were always the same like my pre boil volumes than I would be more inclined to do so. My burner is always set to the same level and the amount of hops I use in the boil really doesn’t vary much. I guess I am just confused…

11

In my experience, if you don’t stir the wort well before taking a reading you can get different results.

12

I am probably doing it incorrectly but I take my “Pre-boil” reading right after the hot break.  I’ve always assumed the wort was thoroughly mixed at that point.

Paul

13

+1.  Same here.  Turbulence of the boil seems to mix things more uniformly.

14

I make sure that I take my samples after mixing the wort thoroughly. I do not however take my preboil reading after the hot break but right after collecting the second runnings.

15

Possible reasons for a lower post boil volume than expected:

  1. Hops absorb wort
  2. Trub left behind that used to be in the pre-boil wort
  3. Wort shrinkage during cooling.

I think the above 3 reasons could easily account for 0.4 gallons ‘missing’

16

You can calculate both mash and brewhouse efficiency in your recipe.

I personally don’t like “Brewhouse Efficiency” on the homebrew scale. Since it is affected by so many unrelated variables, it doesn’t really tell you anything on its own. You end up looking at mash efficiency + other numbers to diagnose an unexpected result.

Either way, its more important to understand the numbers and what they mean to you. If you change your process or change your recipe, can you still get accurate numbers from the software?

17

I’ve experienced inaccurate readings due to stratification by doing that.

18

So accuracy is still a worry if it is well mixed?

19

Thanks. This makes the most sense to me. I am usually determining what my final volume should be by using preboil vol, preboil gravity and postboil gravity. This is obviously not accurate for me and I probably have incorrect approximations in beersmith for estimating volumes.

I think I need to work on calibrating a stick to put in the kettle for volumes…

20

The boiloff / losses entered in the volumes tab are what got me! I had entered some numbers that weren’t always constant and, depending on the beer/brewday, would throw off my expected SG/volume. It took a bit of playing with the numbers (and reading about efficiency calcs) to dial it in.

Now I account for mash efficiency and evaporation in the software, but trub losses manually. I increased my batch size to 6 gallons post-boil, not including trub/hop losses.

YMMV - I adopted this procedure because of my system’s quirks: evaporation rate changes radically with the season and my losses to trub are different based on style.

For getting your kettle volumes: I use a tape measure to find the height of liquid in the kettle, then plug the height into a spreadsheet to get volume.