Pre-Boil Gravity & Mash Efficiency in Beersmith 2

[HopHead73]

I have my brewhouse efficiency set at 65% and my equipment profile all set up correctly.
I did a partial mash recipe and overshot my OG by .001 giving me a brew house efficiency of 68%.

However, my question is about my mash efficiency. I seemed to hit my numbers fine at the end, but my pre-boil gravity reading seemed extremely off. It estimated a gravity of 1.108 @ 73.6% and I got a reading of 1.073 @ 12%.
I mashed with 8.25qts for 6lbs of grains and I batch sparged with 8qts split into two additions.
I use .5gallon of boiling water in the kettle as a mash out when I drain the mash tun. And then I topped off with another .5gallon in the kettle to reach a pre-boil volume of 3.75gallons.
When I get the kettle up to 200degrees I add only 25% of my LME (add the last 75% of extract with 15mins left in the boil) and then I drew a sample and dropped the temp to 70degrees before taking a gravity reading.This is when I got a reading of only 1.073.
Is this the wrong time to take a pre-boil gravity reading?

I'm not sure what I am doing wrong since I was able to surpass my overall brewhouse efficiency in the end.

I did a test and just deleted the 2nd extract addition that is set in the software as a "late addition" at the end of the boil and my pre-boil gravity dropped from 1.108 to 1.058.
So I'm guessing that the formula in the software that calculates the pre-boil gravity isn't taking that late addition into account for some reason, even though other measurements, such as the estimated IBUs, do take this into account in their formula.

 

[Schnitzengiggle]

I believeit is calculating your estimated pre-boil SG assuming you have all of your extract in the kettle, even though you are adding some of it late. That is to say, it is what your actual pre boil SG should be, not what it actually is with only 25% of your extract added.

It makes sense to calculate the pre-boil in total, but change your hop utilization values, because all-in-all the exclusion of some of your extract will obviously increase your hop utilization and such, but you will undoubtedly be adding the rest of your extract in. For BS to accurately estimate your FG it must know your actual pre boil SG.

 

[HopHead73]

Going back and doing some math by hand, I have a feeling that I may want to invest in a refractometer cause I'm thinking my pre-boil gravity reading may be off do to either the kettle top off water and wort not being mixed properly, or sediment in the test tube or something else.
By Beersmith's numbers of a pre-boil gravity of 1.108 @ 3.75gallons I get 405 gravity points and divide that by my final batch size of 5.25gallons I should get an OG of 1.077.

My measured post-boil gravity in the fermentor was 1.075 @ 5.25gallons whihc gives me 393.75 gravity points.
So it actually does seem that I hit my numbers pretty close and that my pre-boil gravity reading must be off, no?

 

[HopHead73]

and I think i have it figured out now.
Beersmith is taking into account my total amount of extract, even though 75% is a late addition, into estimating my pre-boil gravity.

If I take the gravity reading I recorded of 1.073 @ 3.75gallons I get 273.75 gravity points and I add in my late extract addition of 4.95lbs of LME, which gives me 183 points, and together I get 456, which is close to the estimated 405 by Beersmith. And I'm guess it's higher because I had my efficiency set at 65% and I must have gotten a better efficiency from my mash.

So in the future if I want to calculate my pre-boil gravity with a late extract addition I should take a reading and then add to it however many points my late extract addition will add.

 

[Schnitzengiggle]

I believe it is calculating your estimated pre-boil SG assuming you have all of your extract in the kettle, even though you are adding some of it late. That is to say, it is what your actual pre boil SG should be, not what it actually is with only 25% of your extract added.

...and I think i have it figured out now.
Beersmith is taking into account my total amount of extract, even though 75% is a late addition, into estimating my pre-boil gravity.

I hate to say I told ya so.

Cheers!

 

[HopHead73]

I hate to say I told ya so.

Cheers!

Yeah yeah I hear ya hahaha

I just didn't take the time at first to actually do the math and figure out the calculations myself.
And according to these numbers and beersmith I hit a 97.7% mash efficiency and a brewhouse efficiency of 68.2%.
Nice to see that I'm getting higher then my predicted 65% with my new set up