scaling recipes

So I have done around 20 extract kits from northern brewer over the past year. I went from boiling 3 gallons in the kitchen to full boils after about the third kit. I have a question about the hops additions. In beer smith, if I calculate the ibu's for a partial boil, then turn the recipe to full boil the IBU usually jumps pretty high so I have been scaling the hops additions back to drop the IBU to where it should be for the partial boil. Is this correct?

I just finished a brewing the fat tire clone extract kit from NB and I'm going to be doing my first all grain recipe soon. Looking at the same fat tire all grain kit from NB they have the same hops additions for the partial boil as they do for the all grain.

 

Interesting that partial and full would have the same hop contributions and end up the same. Something seems amiss. Hop utilization should be higher with full boils versus partial. Post the recipes so we can take look at them.

 

I would expect the late hops to stay the same, and reduce the bittering hops to get the correct IBUs.
In all honesty it is likely the same hops in either kit for ease of the vendor - no chance messing up and sending the wrong amount of hops if they are both the same

 

1lb DME - light
6lb LME - Munich

Specialty steeping grains - steep for 20 min.
.5 lb - victory
.5 lb - Carmel/crystal 60L

1oz - German perle - 7.1 AA - 60 min.
1 oz - hersbrucker - 2 AA - 15 min.

Plugging this into beersmith with a 3 gallon boil size and 5.1 gallon batch size, the IBU is at 21.44

If you keep the same size and put a 6 gallon boil size with 5 gallon batch the IBU is 31.83. I scaled hops down to .75 oz each to get IBU of 23.87 .

I know its not that big of a difference for this recipe, but I have had IBU difference of up to 50 points on a different kit so I usually scale down battering hops to make up the difference. Sometimes I will add in the extra hops I didn't use during the boil at flameout to get more aroma. It works and I always get great beer but just making sure that this is the correct thing to do.

 

The odd part is if they are advertising the kit as having the same IBU's. It's probably because of the 1oz packets. If you don't cut it back then you'll end with the higher IBU contribution.

However, even at 15 minutes additions there will be still be some IBU contribution.

As stated above though, this is probably why.
Plug it into Beersmith and change the 15 minute addition to 0 and see if it gets you closer and it might get you where you want to be with a little more aroma or you could do a 60 minute bittering addition of .5 oz and another .5 at 30. Either might get you back to the original number. If you haven't actually looked at the AG recipe sheet, they may have the times changed for you.

 

What I was meaning is to leave all the later additions as is so you don't affect the amount of volitile oils in the beer and reduce the initial 60 minute addition down too where the IBUs are correct.

 

I checked both recipes and they both have the same amount of hops and same boil time. Seems weird because its the same beer and you would think that they are going to taste different because of the difference in IBU.

 

Sorry, misunderstood what you were getting at.

I'm sure it would be different due to hop utilization and boil volumes. As stated before, reduce your bittering addition to match your desired IBU's or brew as it calls for and see what the differences are.

 

Thanks for the responses

Cheers and beers