Hop IBU

[cowboy7307]

I am looking at a recipe and its 21Lt i have scaled it to 10lt
hop amount in original is 28g of galaxy 12.3 AA boiled for 40 min to give a ibu of 21.52
On scaled recipe i have put in 6.97g 12.3AA boiled for 40min to give me a IBU 21.6

Does this sound right , seems a large difference in the amount of hops in about half the amount of beer

 

[Minbari]

doesnt seem right to me. I would logically think that it would half the amount of hops for half the beer.

edit: I tried a recipe on my recipe builder (not this site) and 1/2 the beer was 1/2 the hops.

 

[Zambi]

I'm with minbari here, if aa % is the same (like in your example), it should be half the amount.

Just thinking: maybe you put the lower volume down as kettle volume?
And boil off the same?
In that case, your "end" volume will be lower than half the recipe volume and you would need less hop

 

[Brewer #431398]

You can use an IBU calculator, which takes into account the specifics of your brewing setup and the alpha acid utilization, which changes with the volume of the wort https://www.brewersfriend.com/ibu-calculator/ block blast. These calculators often use formulas like the Tinseth or Rager method to estimate the bitterness contributed by hops.

 

[The Brew Mentor]

Did you scale your water too?
I bet you missed that

 

[Minbari]

Did you scale your water too?
I bet you missed that

I don't use this site's recipe builder. You have to scale the water independent of the rest of the recipe?

 

[The Brew Mentor]

I don't use this site's recipe builder. You have to scale the water independent of the rest of the recipe?

I've scaled recipes and the pre boil water didn't change. It's a catch that you have to make when scaling.
It's likely just something on my end and I'm not sure how to fix it, so I just deal with it.
That being said, If you have double the water, the IBU contribution will be significantly different.
Cheers,
Brian

 

[The Brew Mentor]

In 1/2 the size batch, the hops should be 1/2 +/- a gram or so

 

[dmtaylor]

You literally need to use 10/21 as much, or 28 * 10/21 = 13.3 grams. Any calculator that says anything differently is just overly complicating an ESTIMATION tool. If you REALLY NEED to know your IBUs, you would have to measure in a lab. Homebrewers don't usually want to pay that kind of money.

Also... whatever calculator you're using... it doesn't appear to be consistent with the best model either, which is Tinseth. By my calculations, that amount of hops in that amount of beer will give you about 30 IBUs, not 21. Something ain't right with your calculator. Might I suggest... mine? It's a simplification of Tinseth's method that really works, it's accurate against Tinseth within 6 IBUs (so basically plus or minus a hair, since human beings can only perceive differences in IBUs in "packets" or "notches" of 3 or 4 each). Anyone can download and fiddle with it from this location (yes it is absolutely FREE and pretty darn accurate/consistent with Tinseth):

http://tinyurl.com/TaylorIBUCalculator