Author Topic: Help with Pre-Boil Gravity figures  (Read 7525 times)

Offline Bassman

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Help with Pre-Boil Gravity figures
« on: March 03, 2012, 08:19:27 AM »

I have been using Beersmith 1.4 for about 8 years and I am amazed at how much beer I have made without knowing how to use the program properly!

So I have been reverse engineering the program setup based upon my system.  I am a batch sparger that brews 5 gallon batches.

Yesterday I brewed a red ale starting with 10.3 pounds of grain.  I wound up with 9 gallons in my brew kettle with a pre-boil gravity of 9.3 plato.  I boiled this for 90 min to end up with my O.G. of 13.1 plato.  This is exactly the target gravity in Beersmith.  But, if I look at the pre-boil estimate on the brew sheet Beersmith states I should have had 7.6 plato.

So I am trying to go back and adjust to get the brewsheet to read 9.3 plato as a pre-boil estimate but I can not get it to work.

I had a look at the efficiency tab abd input my number there as well.

Thanks for your help!

Offline BeerSmith

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Re: Help with Pre-Boil Gravity figures
« Reply #1 on: March 28, 2012, 09:34:48 AM »
  What I recommend is entering your actual OG, volume numbers into the efficiency tab.  Next use the "actual efficiency" to adjust your efficiency for the next batch (i.e. use this as your new efficiency).

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Offline dharalson

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Re: Help with Pre-Boil Gravity figures
« Reply #2 on: March 28, 2012, 10:59:52 AM »
Gravity figures are kind of meaningless without accurate reference to Volume and Temperature.  Make sure you compensate for temperature by either cooling the wort to the right temperature or getting close (ie < 100F) and adjusting.

The pre-boil gravity is a good measure of your Mash Conversion and Sparge Extraction efficiency.
Based on your starting grain bill and assume average type malts (36 points per lb per gallon*) you have a total of 371 points of sugar (10.3 x 36).  Your gravity of 9.3 plato (approx 1.037 or 37 points) in 9 gallons is 333 total points.  That results in 333/371 = 90% extraction efficiency.  Thats pretty good, maybe too good.  Make sure your measurements of volume and adjustment for temperature are correct.
The only think that really changes (in the amount of sugar) during the boil is the volume.  So assuming your numbers are correct; boiling 9 gallons at 37 (333 total points) down to 13.1 plato (1.052) your final volume was 6.4 gallons.

If those numbers don't match such as you only had 5.5 gallons at 13.1 then I will say that your pre-boil gravity measurements are not correct.

As far as BeerSmith, you need to make sure your equipment is set up correctly and you account for all of the liquid losses throughout the system.  When you get there all the numbers will line up and life will be good.  But more importantly, don't worry it really doesn't matter as long as there beer in the end ! !

* If you don't understand Points per gallon, google John Palmer, he has a good explanation.

Offline Bassman

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Re: Help with Pre-Boil Gravity figures
« Reply #3 on: March 28, 2012, 09:24:31 PM »
Thanks for your replies.

After going through the point analysis, my numbers might not be that off.  If I ended up with 6.4 in the boil kettle, I still have the losses from chilling and what gets left in the boil kettle to be taken out.  For chilling I use a plate chiller that then feeds a post chiller of copper pipe.  I have never measured the exact loss, but it does seem to take some away.  I don't leave too much wort in the boil kettle but I would guess it is at least .2 or .3 of a gallon?

So my question is:  Does the 6.4 number play a role that I am using 5.5 in now?

The pre-boil gravity numbers generated by Beersmith (7.6 plato) are just way too low for my setup.  But the numbers mentioned above are not that far off.  Where is the difference coming from?

If I try to alter evaporation, chiller losses or leftover wort in the kettle I can get the pre-boil number on the brew sheet to match my measurement, but my efficiency number goes out the window.

BTW, I use a refractometer with ATC so I have not been taking temps into account.