Brewing a Kölsch, low alpha acid hops?

[zackattack784]

I'm brewing a Kölsch this weekend. The recipe I'm following is pretty straightforward with 2 hop additions of german hallertau. Most of the information I can find puts the alpha acids of hallertau around 4%. The ones from my homebrew shop are 2.7%. They're made by hopunion. Should I just adjust my recipe to account for the lower aa rating or am I missing something?

 

[FatDragon]

You'll want to adjust your bittering addition to get the right IBU's, but the aroma addition should generally be done by weight rather than IBU.

 

[zackattack784]

You'll want to adjust your bittering addition to get the right IBU's, but the aroma addition should generally be done by weight rather than IBU.

The recipe I'm following has 2 hop additions, one at 60 minutes and another at 30 minutes. I have Beersmith so I can easily adjust for ibus. Should I adjust the 60 minute addition and leave the 30 minute alone?

 

[FatDragon]

The recipe I'm following has 2 hop additions, one at 60 minutes and another at 30 minutes. I have Beersmith so I can easily adjust for ibus. Should I adjust the 60 minute addition and leave the 30 minute alone?

That's what I would do. You'll get fewer IBUs from the 30 minute than if you were using 4% hops, but you should still get the same flavor contribution, so I would make up the missing IBUs in the bittering addition where it's more economical and shouldn't mess with the flavor as much.