Author Topic: Hop adjustment for a partial boil.  (Read 1194 times)

Offline dzlater

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Hop adjustment for a partial boil.
« on: February 15, 2013, 03:28:16 PM »
I was thinking of brewing a 6 gallon batch of beer with an OG of 1.070, and then topping it off with water to yield 11 gallons of a 1.038 session beer.
When I brew this recipe as a 6 gallon batch without top off water my hop additions are:
1 oz of 7.1% aa challenger @ 60 mins.
.5 oz of 6.1% aa Mt. Hood @ 10 mins.
At about 30 ibu's
I am not sure how to adjust the hops for the concentrated boil?
I know I will get less bitterness from the higher gravity boil.
I am assuming I need to adjust for the lower hop utiization from the higher gravity wort, and also increase amount of hops by the % water that I am adding?
If I use brewing software and set it up for a 6 gallon batch @ 1.070 and adjust the hops for 30 ibu's. And then increase that by the 45% top off water will I be close?
Thanks
 Dan

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Re: Hop adjustment for a partial boil.
« Reply #1 on: February 15, 2013, 04:56:39 PM »
You've more or less got it.

The IBU's should be ~twice what you want in the finished beer. as the gravity is a little less than twice the intended finish gravity. I am not sure about specific numbers on utilization reduction do to partial boil though.
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Offline tygo

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Re: Hop adjustment for a partial boil.
« Reply #2 on: February 15, 2013, 05:10:57 PM »
If you're using beersmith you can set it up in the equipment settings for the boil volume, top up water, etc.

I just plugged it in for a 1.038 beer with an 8 gallon boil (assuming 2 gallons of boil off) and five gallons of top off water.   2.5 oz of 7.1% AA at 60 minutes and 1 oz at 10 got me to 30 IBUs.
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Offline erockrph

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Re: Hop adjustment for a partial boil.
« Reply #3 on: February 17, 2013, 06:41:07 AM »
I think most good brewing software covers this situation reasonably well. Brewers Friend lets you input your volume at the start of the boil and the target volume going into your fermenter (which would include your topoff water), and it will do the appropriate IBU adjustments from there.

As you said, there are essentially two factors affecting your IBU calculations here:
- Lower utilization because you have a higher gravity boil
- Dilution of your IBU's when you top off

At 30 IBU's this doesn't pose too much of an issue, but if you're shooting for a super hoppy IPA you could start running into issues where your concentrated wort is maxed out on IBU's somewhere in the 100IBU range, and depending on how much you dilute it you could end up coming out way lower than expected/calculated.

The IBU calculations don't have an upper limit, so it could look fine (i.e., 150 IBUs calculated in your initial wort diluted 1:1 gets you to 75 IBU's), but your actual wort may actually be in the 80-100IBU range and would dilute down to 40-50 IBU's.
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