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.
Along the way, however, our preferences for hop flavors and aromas began to stray from what we historically considered “hoppy.” While so-called noble varieties continue to bear the standard of what hoppy should be in German lagers, American pale ales and IPAs embrace citrus, evergreen, passion fruit, berry, and even dirt-like characteristics.
Many of the hops we prize today for their unique flavors and aromas also have high alpha acid levels that result from such selective breeding for bitterness (Alpha acid percentages sourced from usahops.org and hopunion.com):
- Amarillo: 8-11%
- Centennial: 9.5-11.5%
- Chinook: 12-14%
- Citra: 11-13%
- CTZ: 14.5-16.5%
- Mosaic: 11.5-13.5%
- Nelson Sauvin: 12-13%
- Pacific Gem: 13-15%
- Simcoe: 12-14%
- Warrior: 15-18%
Wort that is heavily dosed late in the boil with such full-flavored, high-alpha acid hops will retain the desirable flavor and aroma compounds while still obtaining the desired bitterness. And some brewers feel that bitterness derived from late hop additions has a smoother quality than bitterness from hops that have been boiled for an hour.
In practice, you should still add at least a small hop addition at the beginning of the boil to help stabilize the wort and keep foam under control. And while a hop bursting regimen can extract significant bitterness in well under an hour, remember that boiling also coagulates proteins, evaporates undesirable compounds, and offers a certain degree of caramelization, depending on the boil time and evaporation rate.
If you’re a hop head, consider increasing the late kettle hops and reducing the initial bitterness charge the next time you brew your favorite IPA. You might just find that it’s practically bursting with hops.