Efficiency vs IBU's - How they effect each other

[Alphaacid]

If I make a recipe for 75% efficiency and I end up hitting say 90%, how does this effect my IBU calculations? I'm really confused on this. It seems logical that my (theoretical) IBU calculation would go down, do to dilution. Can someone please explain the relationship between efficiency, IBU's, and dry hop weight.

I feel for my dry hop, I'm going to keep the ratio the same .5-.75lbs/bbl so as I have more volume I would increase my dry hop weight. But, I can't go back and reboil hops to get my IBU's up, so how will this effect my final product?

Cheers!

[lhall]

It shouldn't affect your IBUs very much, except that alpha acids are slightly less soluble in higher density wort.

[dick murton]

Sorry to disagree with you Linus (very rarely I ever consider that - but I suspect our two interpretations of the question are different - hence the different answer) but if you are going to dilute your beer to achieve the target gravity / ABV, then your bitterness will drop roughly in proportion to the dilution - very crudely in your example, your bitterness will be 75/90ths of what you were expecting, assuming the hop utilisation is the same. With that degree of increase in extract, you might find a slight drop in utilisation, but realistically, I suspect you wouldn't notice the difference.

Of course, if you simply leave the beer at high ABV, then the bitterness will be roughly the same.

If you are fry hopping, i.e. post fermentation, then your hop rate needs to be calculated based on beer volume, and for greater accuracy, also based on hop oil content. Experience has shown that as regards late kettle hop addition for aroma, that this is the case, and so I assume it is likely to be the same for dry hopping post fermentation. Personally I have never had the small brewery to experiment, and validate or otherwise this assumption. I do know that brewers experienced in extensive dry hopping will base their dry hopping rates and blends on aroma strength and character only.

Cheers

[Alphaacid]

So if I am off by 75/90 efficiency, or a 15% difference does that mean I would have had to add 15% more hops to compensate for the increase in efficiency?

Example: 5pbs of hops @ 75% efficiencent. Or if at 90% efficient increase hops by 15%: 5 x 1.15 = 5.75#'s

[dick murton]

There or thereabouts, yes. Exactly what I used to do when actually brewing for a living, not installing & commissioning plant.

[Stephen Eleven]

Agreed, about all you can do now is scale up your dry hop addition to the volume you collected, and on future batches you can scale up your other additions to compensate for your new expected efficiency.