Hop Extract Calculation

[nosoup4me]

Am I doing the math right?

For 40 IBUs:

1. • This calculator is telling me 5.72 ml (http://www.brewbrothers.biz/Hop-****-Extract-Calculator)
     
   • This calculator is telling me 6.66 ml for a OG of 1.054 and 8.1 ml for an OG of 1.070 (http://www.hoprage.com/calculate.php)
     
   • And Northern Brewer (http://www.northernbrewer.com/documentation/hopshot.pdf) is telling me 6.525 ml with 40 IBU /10 IBU = 4.0 ml x 1.8 (for 9 gallons) + ~8% (for being 1.070) - 10% (90 min boil) = (4 x 1.8 = 7.2 + 8% = 7.25 - 10% = 6.525 ml
     
   • And the add on in Beersmith is telling me 9.75 ml

I know I'm screwing this up somewhere. Can you please help me out? I'm also confused as to the OG. Some say pre-boil some say post.


Pre-boil Gravity: 1.054
Post boil Gravity: 1.070 (dextrose will be added <5 minutes to flame-out to raise OG)
90 minute boil.
C02 Extract is from Yakima Valley Hops http://www.yakimavalleyhops.com/CO2HOPExtractCan_p/extractco2hopextractcans.htm

 

[MHBT]

4ml for 60 mins = 40 IBU

 

[nosoup4me]

4ml for 60 mins = 40 IBU

At a gravity of 1.050?

My preboil is 1.054 my post boil is 1.070.

 

[MHBT]

At a gravity of 1.050?

My preboil is 1.054 my post boil is 1.070.

This might help you
http://www.northernbrewer.com/documentation/hopshot.pdf

 

[ScrewyBrewer]

Am I doing the math right?

For 40 IBUs:

1. • This calculator is telling me 5.72 ml (http://www.brewbrothers.biz/Hop-****-Extract-Calculator)
     
   • This calculator is telling me 6.66 ml for a OG of 1.054 and 8.1 ml for an OG of 1.070 (http://www.hoprage.com/calculate.php)
     
   • And Northern Brewer (http://www.northernbrewer.com/documentation/hopshot.pdf) is telling me 6.525 ml with 40 IBU /10 IBU = 4.0 ml x 1.8 (for 9 gallons) + ~8% (for being 1.070) - 10% (90 min boil) = (4 x 1.8 = 7.2 + 8% = 7.25 - 10% = 6.525 ml
     
   • And the add on in Beersmith is telling me 9.75 ml

I know I'm screwing this up somewhere. Can you please help me out? I'm also confused as to the OG. Some say pre-boil some say post.


Pre-boil Gravity: 1.054
Post boil Gravity: 1.070 (dextrose will be added <5 minutes to flame-out to raise OG)
90 minute boil.
C02 Extract is from Yakima Valley Hops http://www.yakimavalleyhops.com/CO2HOPExtractCan_p/extractco2hopextractcans.htm

This old thread seems to be the only one I could find that attempts to address differences in calculating IBUs of Co2 hop extracts. What I've noticed is in the case of Hop **** they refer to "Pre-Boil Gravity = (Post-Boil Volume / Pre-Boil Volume) x Expected Original Gravity Point". As an example using a post-boil volume of 6.45 gallons and a pre-boil volume of 7.60 gallons and an estimated OG of 1.053 the formula looks like this... (6.45/7.60) * 53 = 44.98 which translates to a 1.045 pre-boil gravity.

With a final wort/post-boil volume of 6.45 gallons a boil time of 60 minutes and a pre-boil gravity of 1.045 adding 1ml of hop **** extract will increase the IBUs of this wort by 10 points. While I doubt the OP is still around these days hopefully someone finds my example to be helpful.