Help with IBU adjustment

[JPicasso]

Hey all,

It's been a couple years since I took my brew kit out, and need some help with an IBU adjustment for a full, or larger boil. I'm getting started back up with a brewer's best extract kit. The instructions inside say to put in 1.25 oz of hops for 60 mins, but that it is calculated for 2.5 gallons boiled. I plan on boiling 5 gallons down to 4, then topping off with a gallon of cold water at the end.

I need help determining how much to cut down the hop schedule, or if I should just eyeball it.

Schedule:
1.25 oz .. AA 4.7% 60 mins
1.00 oz .. AA 4.7% 10 mins

My Brewsmith software is on my other computer and online calculators tell me a full boil will produce LESS IBUs. :/

There are 6 lbs of Extract for this batch.

Thanks for any info
-JPicasso

 

[nukebrewer]

I'd have to see both recipes, but my guess is the two recipes have different boil gravities which affects the hop utilization and thus the hop bitterness attained in the final beer. Try making half, or maybe a little more, of the extract a late addition and see what your software tells you.

 

[JPicasso]

I do not have access to software. I just need to know how much to cut the bittering hops.

Cut it from 1.25 oz to 1.0 oz?

 

[nukebrewer]

You could eye ball it if you want, but for a more accurate answer, the original recipe and the scaled up recipe should be posted.

 

[DocScott]

If your batch volume increases and the amt of hops you're using stays the same, your expected IBUs will decrease (IBU = AAU*U*75/V)
I just threw it into my brewing calculations and here's what I get if I understand you correctly (and assume 8GU per lb of extract) so OG: 1.048
recipe (2.5gallon / 3.5 gallon boil):
1.25oz of 4.7AA at 60min = 46.8IBU
1.0 oz of 4.7AA at 10min = 13.6IBU
New volume (4gallon / 5 gallon boil) with 1.048 OG. to keep same IBU:
2.07oz of 4.7%AA at 60 min = 46.7 IBU
1.70oz of 4.7%AA at 10 min = 13.9 IBU
this makes a lot of assumptions (most importantly, that you are adding more extract into the new batch size to maintain the OG) and I just threw this into my spreadsheets without much thought, but seems to make sense on first glance to me. Hope this helps

 

[JPicasso]

I'm not saying it correctly...

The recipe is formulated for 5 gallons total, with 2.5 gallons boiled.

I need to know how to tweak it for the same 5 gallon result with 4 gallons of boiled wort.

 

[nukebrewer]

Ok, so the recipe with 2.5 gal boil gives me ~15 IBU in BeerSmith. The recipe for the 5 gal boil gives me 24 IBU. So to get 15 IBU with the 5 gal boil you need to drop the bittering addition to .75 oz. That's also assuming you are adding all the extract at the beginning.

EDIT: Got my words all bungled up. It reads correct now.

 

[DocScott]

This is more complicated than you may think. I'll make some assumptions:
#1: 1 lb extract yields 8GU, therefore you are going to get about 48GU total. This then means the OG of the "recipe: 5 gallons boiled to 2.5 gallons" is 2.5*48 = 120
#2: I'll assume you don't have any more extract to add, and therefore your OG in the "new batch 5 gallons boiled to 4 gallon" is then 120/4 = 30 or OG=1.030

remember: total points has to do with the final volume, not pre-boil volumes. If you aren't adding more fermentables and are increasing your end volume, your resulting OG will be lower.

If these are correct, then in the original recipe (5 gallon boil reduced to 2.5 gallon) you could expect 51.4 IBU from the 1.25oz at 60min and 14.9 IBU from the 1.0 oz at 10min

To match theses IBUs in 5 gallon boil, reduced to 4 gallons final with OG: 1.030, you would need 2.0 oz at 60min and 1.6 oz at 10min.

 

[DocScott]

I think I totally misinterpretted your post! Are you trying to boil down to 2.5 or 4 gallon, then topping off with water to get to 5 gallons? If so, disregard all of what I just wrote. sorry to complicate this for you. See NukeBrewer's post for the actual info you're looking for.

 

[nukebrewer]

I think I totally misinterpretted your post! Are you trying to boil down to 2.5 or 4 gallon, then topping off with water to get to 5 gallons?

Neither. The intent is to start with 5 gallons, have 4 gallons post boil and then add water to get a final batch volume of 5 gallons. The recipe that came with kit was written for a 2.5 gallon boil so the hop schedule had to be adjusted for the increased hop utilization in the lower gravity wort.

 

[Yooper]

I'm not saying it correctly...

The recipe is formulated for 5 gallons total, with 2.5 gallons boiled.

I need to know how to tweak it for the same 5 gallon result with 4 gallons of boiled wort.

It's not true that wort gravity affects IBUs. It used to be thought that, but even John Palmer says now he "got it wrong" in his first versions of How to Brew.

I'd not adjust at all, especially since the difference in a 1.5 gallon boil difference is negligible anyway.

 

[JPicasso]

Well, this information is odd.
I thought the point of full boils was *better hop utilization.

From what was said, a full boil vs 2.5 gal boil yeilds lower IBUs for the same hop schedule and same final volume.

 

[nukebrewer]

It's not true that wort gravity affects IBUs. It used to be thought that, but even John Palmer says now he "got it wrong" in his first versions of How to Brew.

I'd not adjust at all, especially since the difference in a 1.5 gallon boil difference is negligible anyway.

Yooper,
If I remember a post of yours (may have been someone else, though) I read recently correctly, you said that Palmer said that break material can absorb some of the hop's alpha acids and that's the real cause of lower utilization. Please correct me if I'm wrong, but doesn't a higher gravity equate to more break material and thus lower hop utilization? If that's true, then boil gravity may not be the direct cause of lower hop utilization, but you can still make it a function of gravity based on the relationship between gravity and amount of break material. I'm not an expert, so I will welcome any corrections, but logically this makes sense to me.

 

[ludomonster]

Well, this information is odd.
I thought the point of full boils was *better hop utilization.

From what was said, a full boil vs 2.5 gal boil yeilds lower IBUs for the same hop schedule and same final volume.

I think you're confusing yourself. A full boil will have better hop utilization than a partial boil. So, a full boil will have higher IBU's.

It's probably not a big deal and you should just brew it. If it comes out too bitter and you want to brew it again. Fix it then.

 

[JPicasso]

I think you're confusing yourself. A full boil will have better hop utilization than a partial boil. So, a full boil will have higher IBU's.

It's probably not a big deal and you should just brew it. If it comes out too bitter and you want to brew it again. Fix it then.

HA. But that is what I am trying to avoid. I wanted to get as close to what is expected than trial an error. It's a kit, and I've not used many kits w/o mucking with them. And the numbers turn out lower IBUs with a larger boil, that's what was confusing me.

Anyways, I ended up using 1 oz hops for 60 mins, .25 oz for 30 mins and the last ounce at 10 mins.

It's in the fermenter as of late last night. Should be beer.