Calculating the Numbers – Late Hop Additions
To use this technique in your own beers, replace all or part of your traditional bittering hop additions with additions at 20 minutes or less left in the boil, increasing the amount of hops to get the same IBUs. Replace all of your bittering hops for an intense hop flavor. Replace a lesser amount to just enhance the hop flavor.
While isomerization is limited during a short boil, hop utilization isn’t linear across the boil time. You don’t need 6 times as much hops for a 10 minute boil as compared to a 60 minute boil. Assuming you’re getting about 30% utilization at 60 minutes, you’ll get around 17% at 20 minutes, 14% at 15 minutes, and around 10% at 10 minutes. So you’ll need to approximately double or triple your hops to get an equivalent bitterness. If you’re already calculating your bitterness with software or some other tool, use the same method to make this adjustment.
It is said that most formulas for calculating bitterness are not as reliable for very late hop additions, but don’t let that stop you. It is quite difficult to detect a 5 IBU difference in most moderately bittered beers and impossible in a highly bittered beer.
In beers with significant bitterness (50+ IBU), you might still want to add a charge of high alpha hops early in the boil. If you don’t, the amount of hop flavor can completely overwhelm some beers.