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So for the NB Innkeeper, I've read the ibu's should be mid 30's, and their extract kits account for partial boil.
The same additions once scaled for a 6 gallon boil shoots to mid 40's.

I'm guessing the simplest way to roll back the ibu's would scale the 1oz fuggles(60min) to .6-.75 oz would keep it mid 30's.

How much would i expect this to alter the actual recipe's flavor, considering the flavor/aroma additions will be in line with the original recipe? http://www.northernbrewer.com/documentation/beerkits/Innkeeper.pdf

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2 Answers 2

up vote 2 down vote accepted

In your position, I'd just brew it, and see how you like the outcome. Many factors affect perception of bitterness - it's far from an exact science.

For instance, if the recipe has been stored for any length of time at room temperature, the hop alpha acids in some hop varieties will have deteriorated up to 50% in 6 months.

But let's look at the theory all the same.

You said you want to target 6 gallons, but the recipe calls for a target of 5 gallons, so let's use that so we're not complicating things by introducing dilution into the picture. The partial boil was 2.5 gallons, and full boil is 5 gallons. The OG given is 1.043, so 1.040 in round figures.

John palmer gives a table showing the utilization factor for hops for different boil times and gravities. The recipe has two additions - one at 60 mins and the other at 45mins. The reduction in hops required going from a partial boil to full boil is:

  • for 60 mins: 0.176/0.252 = 69.84%
  • for 45 mins: 0.162/0.232 = 69.82%

So, reducing both additions to 70% of their original, 1oz down to 0.7oz will, at least on paper, get you down to the same region of IBUs.

If you then wanted to scale this up to 6 gallons, then multiply the hops and grist in the recipe by 1.2.

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I would not scale my hop additions based of a partial to a full boil (assuming both are five gallons in the end). If I'm going to scale my hops at all, it will most likely be based on the difference in alpha acids from harvest to harvest, but even that's pushing it.

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Hop utilization is affected by wort gravity, so moving from partial to full boil does require scaling the hops. –  Tobias Patton Mar 29 '12 at 18:21

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