Add my hops at wrong time. Does it really matter? (math inside)

[Cltroutman]

I have been lurking on these boards for the last few weeks and I have got to say there is a lot of very informative threads. Thank you everyone for letting me learn from your mistakes! Anyway I finally hit my first mistake in my fourth batch of homebrew. Sunday I brewed up a 5 gal. batch of Milk Stout from a Brewer's Best kit and added all my hops at the beginning of of my 60 minute boil.

So my questions:
I was trying to figure out how I could added some additional aroma hops, since I missed out on adding them at the right time, and if anyone had a recommendation for what would work? I have been reading Palmer's How To Brew and it appears I can added dry hops to the secondary without increasing the IBUs. Should I just go out and get another .5 oz of Willamette hops and dry hop them in? How does dry hopping change the profile vs. adding them the last 10 minutes of the boil?

I don't think this blunder will effect the final product too much. One, it is a stout so it has a high boil gravity. Two, I am not sure I will reach the kit's IBU range of 31-34. It appears the difference between adding the Willamette at 10 minutes left in the boil and at the beginning of the boil is ~3.5 IBUs (math below). Can someone explain to me if my math is correct?

Recipe:
6.6 lbs. Special Dark LME
.5 lbs Lactose
.5 lb Maltodextrin
8 oz. Carmel
4 oz. Roasted Barley
4 oz. Dark Chocolate
.5 oz Warrior Bittering Hops (Alpha Acid 17.2%)
.5 oz Willamette aroma hops (AA 4.7%)

Boiled in 2.5 gal. of water.

Going through the math:

AAU = Weight x %AA
Warrior .5 oz X 17.2 = 8.6 AAU
Willamette .5 oz x 4.7 = 2.35 AAU

Gravity of the Boil
.lbs LME x 36 / Vboil (my understanding is that 36 is a constant for LME and 40 for DME)
6.6 .lbs x 36 / 2.5 gal. = 95 so OG 1.095

IBU = (AAU x U x 74.89) / Vrecipe

74.89 is a constant for the conversion of English units to Metric
U based off Table 7 - Utilization as a function of Boil Gravity and Time

Warrior IBU(60) = (8.6 x .154 x 74.89) / 5 = 19.8
Willamette IBU(60) = (2.35 x .154 x 74.89) / 5 = 5.4

If done correctly: Willamette IBU(15) = (2.35 x .055 x 74.89) / 5 = 1.9

I calculate my IBU at 25.2 rather than 21.7; both which are not near 31 - 34 labeled on the kit and assuming a 1-3 IBU error margin.

Either way I know at the end of the day all that really matters is that the final product tastes good. But I think understanding the basic principles will only make my beer better.

 

[Kaz]

You can certainly add some Williamette to dry hop. The main difference between adding at 10mins left in the boil and dry hopping is that dry hopping will add very little bitterness or flavor and mostly aroma. Boiling for 10mins would've given you a little more IBU and some flavor. I say go for it and add the .5 Williamette to dry hop for 7-10 days after primary fermentation is mostly done.

 

[badhabit]

It matters but you may not notice...particularly in a stout....also would be good to know final batch size...assume it is 2.5 Gal. You can not correct the bittering....already too late when you added but you can add for more aroma and taste. As noted that can be done as dry hop for notable change in aroma. You can add from about 20 min remaining in boil on to make the changes. Just remember that flavoring from hops reaches maximum utlization at about 20 minutes, aroma maximum utlization is reached at about 7 minutes, all additions contribute to bittering but not as much in the first ten minutes, that maxes out at about 60 minutes but continues to contribute throughout 90 minutes.

 

[Cltroutman]

It matters but you may not notice...particularly in a stout....also would be good to know final batch size...assume it is 2.5 Gal.

Final Batch was 5 gal.

Thanks for the feedback. I am going to dry hop some Williamette and report back.

Can anyone give me some feedback on why my calculated IBUs are so low? The kit says it should be 31-34?

 

[Kaz]

I'm at work so I didn't really have the time to check the math, but a quick plug into Beersmith with your recipe and a 2.5 gallon boil gives me a final IBU of 15.4 with both hops being added at 60mins.