# Incorrect OG?

Discussion in 'Recipe Editor' started by TexasWine, Dec 11, 2017.

1. ### TexasWine New Member

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#1
Long time user here, but ran into a problem I can't seem to find an answer to.

I built a recipe with a pre-boil gravity and volume of 1.062 and 7.5 gallons, respectively. Boil off is 0.75 gallons. I add one pound of sugar at the end of the boil. Based on that math I should have an OG off...

Pre-boil gravity: 1.062
Pre-boil volume: 7.5 gallons
Boil Off: 0.75 gallons
Post-boil volume: 6.75 gallons

62 gravity points / (6.75 gallons / 7.5 gallons) = 69 gravity points

Calculated post-boil gravity: 1.069

Add 1 lb sugar late in the boil, which should be ~46 ppg.

46 points / 6.75 gallons = ~7 points total

Estimated gravity to the fermenter: 1.069 + 1.007 = 1.076 OG

The recipe builder is telling me my OG should be 1.085.

Anybody got any good ideas as to what's going on? I'm confident in my math, but why is BF giving me such a drastically different answer?

2. ### Ozarks Mountain Brew Moderator Staff Member

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#2
never base your recipe on the "Boil Gravity: (recipe based estimate)" that’s in the recipe editor, it’s not a constant, too many variables can change that, is this what you’re doing?

3. ### TexasWine New Member

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#3
I was simply using the Boil Gravity as a check, but i verified that what BF gave me is in fact correct. I had 20 pounds of grist, mostly 2-row.

20 lbs @ 36 ppg = 720 gravity points

According to Kai's numbers for theoretical maximum of first wort (I'm a no sparge brewer), I could expect 87.3% extract maximum.

720 x .873 = 629 gravity points

Strike volume = 9.75 gallons

629/9.75 = 64

Maximum theoretical pre boil gravity would be 1.064. I actually got 1.063 for this brew, so my conversion was really good (did a Brauwelt Hoch-Kurz mash) and I started the boil of 7.5 gallons with almost the maximum possible gravity.

I just can't figure out why the heck BF told me my OG was supposed to be 1.085. Just doesn't make sense given the math I did above and the boil off I entered and the sugar addition.

FWIW, my brewhouse efficiency was set at 63%. Batch size was 6 gallons to the fermentor, losing 0.75 gallons as trub and dead space in the boil kettle.

4. ### Ozarks Mountain Brew Moderator Staff Member

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#4
and I'm guessing you've dialed in your defaults with your profile? that makes a huge difference but one thing to we like to say is don't cross formulas with different websites, get your readings from one, change your defaults and losses and go from there, every website has a different formula but Ill pass it on to the developers just the same

5. ### TexasWine New Member

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#5
Yup, my defaults have been the same for a while now. I measured all my dead spaces and other equipment losses, evaporation rate is spot on. It's just the OG on this recipe/batch was wonky, even though I hit all my other expected numbers of volume and gravity leading up to flame out.

6. ### Myndflyte Active Member

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#6
I guess the real question is, have you brewed this yet and what was your OG?

7. ### TexasWine New Member

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#7
Yup. OG was 1.074.

I think I might have found the my issue. Does BF assume 100% extract efficiency, meaning if there are 36 ppg available, then that's what brewers will get? It appears so because my pre boil ppg is calculated at 25.2 and the pre boil efficiency was 69%.

25.2/36 = 0.70 or 70%

8. ### Hobbes Member

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#8
I'm having other issues, regarding OG/IBU and kettle vs fermenter settings with BH/Eff. Found this thread while searching and i checked and my pre-boil gravities all appear pretty spot on. Even if it was counting the sugar addition, it prob shouldn't have been as high as 1.083.

I've noticed that regardless of picking "fermenter" or "kettle" the efficiency number determines the pre-boil calcs. For example, i have 72% Bh and one recipe i have calls for 1.047 pre-boil at 8.3gal. On brew-day if i get this and input it the value displayed for mash eff is "72". I actually got 1.051 because my eff is not 72, it's 80-90% but my total brewhouse is 72. I'm most def using the formulas/values incorrectly and started another thread to get some help. I currently stick to putting "mash eff" here and doing calcs based on "ending kettle".

For you though, with a 63% brewhouse eff entered i'm not sure why the OG would have been so high unless your pre-boil vol was set low. Can you make the recipe public and share it briefly so we can see the values?