15.5 °Brix hydro reading at time of pre-pitching
[s]My actuals gives confirmation that hop absorption equals about 0.06 gallons per ounce.[/s]  I have 37 L fermenting away.... 

"My actuals gives confirmation that hop absorption equals about 0.06 gallons per ounce."
I don't understand this, and perhaps this is way too complicated to discuss on this forum.
What do you mean by "hop absorption", and how do you determine that the rate is .06 gallons per ounce?

Streamer wrote:What do you mean by "hop absorption", and how do you determine that the rate is .06 gallons per ounce?

Thank you for your question.      Ah, you made me re-look at my figures and I had it wrong.....
I did some Googling on hop absorption rate and found a bunch of different rates from 1:8 to 1:12, higher if they didn't squeeze.

Let me explain my figures from the screenshot above
Section K
I use a sight glass so I tend to stop my boil at the point of flame out listed in Section K.  My 90 mins. boil was extended to 100 mins. to hit that target.  At VFO, it was 12.33 Gal. with the 45 mins. and 30 mins.hop additions in hop bag #1 in the wort (not squeezed) The VAW calculated at 11.85 Gal. (VFO/VAW assumes hop bag(s) at time of flame out is NOT pulled)  Hop stand hop bag #2, added at flame out for a 15 mins. hop stand.
Section L
I siphoned out of my no chill containers one week later.  I filled 2 corny keg fermenters to the welded seam (18.5 L each), with 350 ml to spare.  I measured the remaining sludge (5.75 L).  My measured VAW is 11.39 Gal.
The Math - "Wort retained by hops"
11.85 Gal. VAW - 11.39 Gal. VAW = 0.46 Gal or 59 oz. (hop absorption for 5.5 oz of hops plus 15 mins. of evaporation).
Used hop flowers in two paint strainer bags, pulled and squeezed as dry as possible with two pot lids.
 I lost maybe 24 ozs. due to evaporation and about 35 ozs. due to absorption. 

I made more edits, so if anyone wants to add to this discussion, please do so.

I think I was interpreting this backward. By hop absorption, do you mean the amount of wort the hops absorb?

Another question born of ignorance. To hit your VFO in section K, I assume you turn off your heat source and then measure. Do you find that hitting the VFO in this manner helps you hit the gravities you're looking for? I think I understand that by trying to hit the VFO in section K you had to boil for an extra 10 minutes. Conversely, would you boil for less than 90 minutes if you hit your VFO early? My guess is not, because by doing so you wouldn't have given the grains enough boil time to completely convert. 
Thanks for your feedback. This is an informative thread

Streamer - PP has previously noted http://beta.brewer.info/viewtopic.php?f=41&t=3551 that the BIABacus sets things up to slightly exceed the target Specific Gravity (OG) so that you have a cushion and can, if you wish, dilute as wort goes into the fermenter. You should also read this thread about dilutions.
There is Section X to enter your own boil-off rate based on your experience (keeping in mind that brewing outdoors presents more variables such as wind, temperature and relative humidity for you to include in any adjustment numbers). Hitting your VFO early or late and then using that as your end-of-boil (EOB) signal, rather than the clock, is just another way you can choose to operate. If you want to brew a particular recipe repeatedly with a narrow range of consistency in measurements, perhaps VFO is a good one to target. I, for one, don't seek that level of consistency whilst brewing a variety of recipes.
Your comment

    My guess is not, because by doing so you wouldn't have given the grains enough boil time to completely convert."

needs either rephrasing or outright correcting - conversion happens during the mash, not the boil. The bag containing the grains has been removed prior to the boil. The boil does denature proteins and cause precipitation of less soluble matter and there is some carmelization of sugars and some other chemistry going on, hops are doing their thing during the time in the boil and until they cool off a bit, but the boil is otherwise mostly for volume reduction.
[Off-topic, I'd like to rotovap wort at various temperatures, then add hop teas and see what results]
Check out the links I mentioned and ask again if not clear, OK?

Thanks ShorePoints. I'll study the links.
Of course the grains are not boiled - I should be more diligent in thinking before posting.

Streamer wrote:I think I was interpreting this backward. By hop absorption, do you mean the amount of wort the hops absorb?

Thank you for that.   I did a search on "hop absorption" from Pistol Patch and found one hit where he labels it as "Wort retained by hops"

Tastes great  .  Very pleased with the attenuation (81%), thanks to Rick's help on my Bru'n Water file.

3 °Brix reading on the hydro

Wow! That looks beautiful 

I got a 80.7% attenuation, comes in at a 6.7% ABV beer.  This is my version of the Bells Two Hearted Ale.

I brewed this recipe again - March 11 2017.

Last time was over Thanksgiving holiday. Both were double batches and they were the first and second brew in my new 20 gallon kettle. The grain absorption rate was set at 0.6 l/kg the first time around and worked out well for me, in fact came out with a little more volume, so I used that value again. This brew for some reason fell short of the expected volume after the bag pull. Upon evaluation after the mash I figured it was 0.74 l/kg. I was short 2.4 L at VIB.

My Thanksgiving brew had an 11% evaporation rate and I was purposely targeting 8% this time around. I ran a test boil off rate prior to check what new power setting I needed to use. Previously at 65% power, I determined that 55% would hit 8%.

Knowing that I missed my volume when I pulled the bag, I went into panic mode and started calculating "what-ifs". I really wanted the same VFO if it would work out okay. I had to use my refractometer this time to help "guess" gravity. I got on realbeer.com/hops and ran a scenario for a new 30 mins. hop addition. I ran with this and decided to eliminate my hop stand.

Today was yeast pitching day (3-22-2017). My VAP 39.90 l, OG 1.058/1, IBU 55.3, B/G Ratio 0.953

My evaporation rate was 6% and I took a hit on efficiency at 68% (estimated 76.6%)

Here is the recipe below. I will post more actuals and photos on the next post.

I Heart Me - American IPA - Batch 12
Brew Date 3-11-2017

Brewer: Mad Scientist
Style: 14B
Source Recipe Link:
ABV: 6.6%
Original Gravity (OG): 1.063
IBU's (Tinseth): 55
Bitterness to Gravity Ratio: 0.87
Colour: 14.3 EBC = 7.3 SRM

Kettle Efficiency (as in EIB and EAW): 76.6 %
Efficiency into Fermentor (EIF): 66.6 %
Note: This is a Pure BIAB (Full-Volume Mash): Sacharification

Times and Temperatures
Mash: 90 mins at 66 C = 150.8 F
Boil: 70 min

Volumes & Gravities
(Note that VAW below is the Volume at Flame-Out (VFO) less shrinkage.)
Total Water Needed (TWN): 56.75 L = 14.99 G
Strike Water Needed (SWN): 57.87 L = 15.29 G
Volume of Mash (VOM):
Volume into Boil (VIB): 51.4 L = 13.58 G @ 1.057/2 = 14 °P
Volume at Flame-Out (VFO): 46.66 L = 11.85 G with hop bag(s) in
Volume at Flame-Out (VFO): with hop bag(s) squeezed and pulled
Volume of Ambient Wort (VAW): 44.86 L = 11.85 G @ 1.063 = 15.4 °P
Volume into Fermentor (VIF): 39 L = 10.3 G @ 1.063 (Set in Section B, by brewer)

Forecasts By MS
Kettle to Fermentor Loss (KFL): 5.86 L (Estimated in Section X)
Estimated Wort Retained By Hops Loss: 0.94 L (total ozs. of hops x 0.045 G)
Estimated Volume into Fermentor: 38.06 L
Est. Final Gravity (FG): 1.012 = 3.0 °P

The Grain Bill (Also includes extracts, sugars and adjuncts)
84% Rahr 2 row (3.5 EBC = 1.8 SRM) 10463 grams = 23.07 pounds
10% Wey Munich type 2 (25 EBC = 12.7 SRM) 1246 grams = 2.75 pounds
6% Crisp Caramalt (52 EBC = 26.4 SRM) 747 grams = 1.65 pounds
Total Grain Bill weight 12456 grams = 27.46 pounds

The Hop Bill (Based on Tinseth Formula)
[actual hop bill used the day of the brew]
35.3 IBU Centennial Flowers (9.9%AA) 73.9 grams = 2.60 ounces at 80 mins (First Wort Hopped)
19.7 IBU Centennial Flowers (9.9%AA) 56.6 grams = 1.50 ounces at 30 mins


Miscellaneous Ingredients
1.00 Whirfloc (Boil) 5 Mins - Clarity

Chilling & Hop Management Methods
Hopsock Used: Y
Chilling Method: No-Chill

Fermentation & Conditioning
Fermentation: Safale US 05 for 21 days at 18.4 C = 65.12 F
Secondary Used: N
Crash-Chilled: Y
Filtered: N

14.3 °Brix

Just finished my 1st 5 gallon keg, so here is a photo of a 3 ounce draw from the 2nd keg.


Outside on the porch railing