The practice relies on generous additions of hops in the final fifteen or so minutes of the boil to extract flavor and aroma with only moderate bitterness. If you want to send your homebrew’s hop character into the stratosphere, give hop bursting a try.
Traditionally, a brewer adds a dose of hops to hot wort soon after it begins to boil. The wort then boils for 60-90 minutes for a handful of reasons, one of which is that a long boil squeezes more bitterness from hops than does a short one. In the past, when alpha acid levels (bitterness potential) were relatively low, an upfront bittering charge followed by a long boil was essential for balancing malt sweetness with hop bitterness.
But a beer that might have historically been bittered with hops containing 6 percent alpha acid could achieve similar bitterness from half as much, by weight, of a hop that’s 12 percent alpha acid. So hop breeders began developing high-alpha acid hops that could contribute bitterness with less vegetal matter in the kettle. And because an hour or more of boiling drives off most of a hop’s aroma and flavor, the sensory characteristics of bittering hops are less critical than those of hops that will be added later in the boil.