Getting 50+ Ibu Into A Batch From A Partial Boil

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Big E

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Hi Guys, im about to make my first Russian Imperial Stout, im doing extract with speacialty grains based on the Brewing Classic styles recipe. My questions is regarding partial boils and IBU's. I heard on the Can You Brew it podacast that the maxium amount of IBUs you can get into a beer is about 100, so by doing a partial boil and then diluting to volume up to final batch size the maximum IBU's you can end up with in the final beer is around 50 (assuming your boil is around half the size of batch volume) . In the recipe im shooting for around 70, so my question is how do i go about getting the desired IBU's to make it through to the final beer ?

Is this correct or am i missing something ?

Do i need to make a hop tee to extract more from the hops and add back the batch ?

Should i even worry about it if my partial boil gravity is adjusted to be the same as the recipe pre boil gravity ? :unsure:

Is the 100 IBU figure a measured value or maxmium amount of IBU that can be perceived in the beer ?

When i do my partial boils i make the pre boil gravity up to the recipe gravity and then add the rest of the malt extract towards the end of the boil. My pre boil volume is 13.5L

Any help would be greatly appreciated

Cheers in advance E
I may be sticking my foot in my mouth on this.

The IBU limit of 100 is what you can taste. Or once it is bitter it is bitter and you can not tell any more.

So I would go for the 70 IBU you want in the recipe by adding the same amount of hops to the partial boil as you would for a full boil. You could put in a bit more if you feel better. A 80 IBU RIS is not going to be much different then a 70 IBU RIS.

Just my oppionion.
Are you using any brewing software like beesmith/promash etc?
If you are adding lme/dme after the boil the you can click on that ingredient in the recipe and check "add after boil". Also adjust your boil to what it is and use the top up water in fermenter bit. BS will work out the correct IBU based on what you tell it you are doing. When I do extract beers I, like you are, only boil half the volume with half the dme and add half the fermentables at either flame out or with 10 mins to go.
Yeah thats the method i use when doing partia boils, Beersmith gives me the same IBU,s with the partial boil and late extract addition as for the full boil. So i guess ill give it a go and see what happens, just really want to make sure i get this one right given the extra cost involved and 6 months + ageing period.

Cheers for the responses

Big E
That's because the gravity is the same. If you boil full volume with all the fermentables it's the same as boiling half the fermentables in half the volume, IBU wise. Boiling half volume with half the ferm's will give you better isomerization than boiling half the volume with all the ferm's. No issue if you need to use all the ferm's and top up later, you're just using (read: wasting) more hops. But if you go down that road, and I have in the past, I'd only adjust the 60 min addition to up the IBU's to suit
Cheer Penny, i guess i was just getting hung up on this 100 IBU thing.

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