Why Add Hops at Different Times?

If you've ever wondered why hops are added at different times in the boil kettle the plot below sums it all up pretty clearly. The horizontal axis is the amount of time the hops are boiled while the vertical axis is the amount of the effect obtained from the hop addition. Hops intended to add bitterness to the beer are typically added early so that they are boiled for 60 to 90 minutes. Flavoring hops are added somewhere around 20 minutes before the end of the boil. Aroma hops are added less than 10 minutes before the end of the boil. Oftentimes different hop varieties are used at these different stages since they each have their own individual characteristics.

NOTE: Unfortunately I do not remember where I gleaned this handy plot so I am not able to give proper credit to the originator. So I guess the only attribution I can provide is "Somewhere on the internet".

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