Low IBU increase boil time?

I ordered ingredients for a recipe but the AAUs for the hops turned out to be 3% instead of 4.4%, which is what my recipe requires.

My recipe IBU originally was 59 but now it is 41 with the lower AAU hops.
Can I just increase the boil time of the hop additions or do I need to purchase more hops.

I am using Crystal hops in the recipe and do not have a substitute. All I have on hand besides the Crystal are Saaz and Northern Brewer.

You could do a late extract addition and your IBU's will be higher.

Edit:- I just realized I didnt answer your question. I dont believe extending your boil time will improve your hop utilization. Maybe give it a quick search just to be sure.

Pharmguy said:

You could do a late extract addition and your IBU's will be higher.

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This is an all-grain recipe. Is there an all-grain trick?

Ahhhh, all grain.....I dont know as I do PM's. Hopefully someone else chimes in for ya.

More boil time won't make up that many IBU. You need to add more hops.

What you can do is brew the low IBU now. Get more hops later. Boil them in a quart of water in a saucepan for however long the original boil was. Add to fermenter. I've done this several times to increase the bitterness and/or aroma of beers that were still in the fermenter.

Going from a 60 minute boil to a 90 minute boil will only increase IBUs by 10%. I'd make up the IBUs with a little NB.

He could have lowered the batch, couldnt him?

Grams of hops = volume in litres x IBU / utilisation / AAU / 1000

Grams = 25 x 37.5 /.2 /.062 / 1000 = 75.6 grams

Just accommodate the hops you have with the right volume for the IBU required . Add more crystal .

Hope this helps