Do I need to adjust for a partial boil?

[TwinIon]

I'm trying out my first recipe that uses some grains, and I just got back from my LHBS with all my ingredients for the dopplebock. I was just looking over the recipe again and I realized that the recipe calls for a 6.5 Gal boil (down to 5). Unfortunately, I don't yet have a setup that can do a full boil. My stove can't keep much more than 2.5 gallons at a boil. The recipe is as follows:

6lbs dark DME
4lbs German Pilsner
2lbs Munich Malt
1lb Crystal Malt 30L
1lb Chocolate Malt

Bavarian Lager yeast

1.5 oz Hallertauer 60 min
.75 oz Hallertauer 30 min
.5 oz Hallertauer 15 min
.25 oz Hallertauer 5 min

I recall reading about hopps in particular needing to be adjusted for full boils vs partial boils. Is this a case where I'll need to adjust something, or will it work out with a 2.5 gal boil? Thanks for any help.

EDIT:
I was reading through some similar threads, and there seems to be conflicting info. I was messing around with Beer Calculus, and something seems off with either their algorithm or (more likely) my recipe.

I put the recipe in with a 5 gallon boil and it comes out as a 16.1 IBU, rather than the ~32 the recipe indicates.

Then I tried to tweak it to get to around the same and I'd need ~8 total oz of hops rather than the 3 oz that are in the recipe. That seems like a whole lot, but I'm pretty new to this.

Even more, to get to the ~32 IBUs that the recipe indicates, I'd need ~ 14 oz of hops. Not only does that seem like a whole ton, that's a decent amount of money. Please tell me I don't need to spend another $50 on hops to make this work.

 

[cshamilton]

I don't know the exact adjustment, but you will get less hop efficiency with a smaller boil. Do the biggest boil you can.

Assuming you are steeping the grains for a while you could throw your 60 min hops in there - either throw them in the water or in a bag separate from the grains. You could also consider a longer boil but that would only help with the bittering.

I think beer calculus will let you play around with these, it should at least give you an idea.

Also you could think about using something with a higher AA% for the first hop addition.

 

[gypsyhead]

search the forums for Late Extract Addition. there is debate as to whether the dissolved sugars or dissolved solids in the wort detract from the hop utilization, but it seems like everyone agrees that waiting until later in the boil (say the last 15 minutes) to add your extract will allow for better hop utilization (ie. fewer hops give a greater effect)

 

[Calder]

That's a big beer. How are you planning on mashing 8 lbs of grain and ending with 2.5 gallons to boil.

My estimate is that is going to come in around 1.100 (assume 80% mash efficiency). BeerSmith puts that around 34 IBUs doing a full boil, using Rager, which is what I prefer to use.

Going down to 2.5 gallons, it gives 22 IBUs. Adding an extra ounce to the 60 minute addition gets it back to 33 using the same recipe assumptions.

14 ozs of hops for $50!!!!!! If you think you are going to use a lot of hops, buy in bulk. 1 lb of Hallertau from Hops Direct is about $11. Add shipping and it's about $20; a lot cheaper than you are getting. Buy lots more and the shipping cost (per lb) goes down considerably. I buy my hops from there and (including shipping) it works out at $0.62 per ounce. ....... I do buy a lot of hops.

 

[Calder]

search the forums for Late Extract Addition. there is debate as to whether the dissolved sugars or dissolved solids in the wort detract from the hop utilization, but it seems like everyone agrees that waiting until later in the boil (say the last 15 minutes) to add your extract will allow for better hop utilization (ie. fewer hops give a greater effect)

No debate; lower gravity = higher hop utilization. Late extract addition will increase IBUs, but it's not that much ..... yes, you can do the calculations, and get different answers for different gravities and times for additions, but it generally works out to around 10%.

 

[Qhrumphf]

Check which scale the recipe is using for IBUs. Beer Calculus defaults to Tinseth. They also calculate "average" boil, so if you can figure out how much boils off, you take the starting volume, the ending volume after the boil, and calculate the recipe based off the number in between (ie if you start with a 5 gallon boil and boil off 1 gallon, you'd base the recipe on a 4.5 gallon boil). Doing it that way, I get within the same general area between Beer Calculus, BeerSmith and BrewMate with all set to Tinseth. I'd also check the AA values on the hops you have. I find there's a lot of variance between what Beer Calculus says the AAs are and the hops I get from the LHBS.