Putting the Bite in Your Beer
When and how you toss the hops into your boil kettle matters. Add them early and you get a blast of bitterness. Add them later and you perfume the brew. How do you know just when to add them and how your beer will turn out? The longer the hops are boiled, the more alpha acid converts to isohumulone.
The additional bitterness comes at a cost; the boiling action drives off or destroys the delicate oils that create the aroma and flavor. Hop additions named “bittering,” “flavor,” or “aroma” describe the goal of the addition, but even “bittering” hops add flavor.
The basic hopping rules of thumb: Boiling hops 30 to 90 minutes adds bitterness. The 15-to-30 minute mark promotes hop flavors. You can capture aroma by adding hops between zero to 15 minutes.
Don't boil hops more than 90 minutes. The hops break down creating strong vegetal favors. If you need more bitterness, add more or stronger hops.
Other Hop Uses
There are more places to hop than the boil, each with different end effects. Each is designed to boost hop presence without boosting bitterness. In order of addition:
Mash Hopping — Brewers can toss a couple of ounces of hops into the mash bed. The actual effect is subtle and may not be worth the extra cost.
First Wort Hopping — An old German technique revived by homebrewers. It involves taking flavor additions (twenty minutes) and putting them in the kettle during mash runoff. The resulting flavor and bitterness rates favorably in blind tasting panels.
Dry Hopping — Widely used to boost hop aroma, dry hopping involves adding fresh hops during secondary fermentation. Over several weeks, fresh hop aroma suffuses through the beer. Dry hopping imparts no additional bitterness.
There are different hop packages that you need to sort out. Each has advantages and disadvantages:
Whole flower — The cones are picked straight from the vine and dried in a hop roast to prevent rot. Many swear by them, but they can oxidize quickly even in vacuum-packed bags and bitter less per ounce than pellets.
Pellet — Most brewers use pelletized hops. Dried whole hops are passed through a hammer mill that crushes the flower and lupulin glands into powder. They are pressed together into tight pellets. They store better than whole hops and bitter more efficiently. Purists contend the aroma is inferior to whole hops. This book's recipes are formulated for pellets.
Plug — A medium between whole flower and pellets, plugs are lightly crushed and compacted into half-ounce tablets. Developed for the British cask beer industry for easy dry hopping.
Extract — The “better living through chemistry” solution of hop oils. Brewers choose a bittering or aroma extract, measure, and add. Before you dismiss the notion completely, several top-flight, award-winning microbreweries use bittering extract to reduce wort loss to hops.
When brewers talk about beer bitterness they talk about “IBUs” or international bittering units. This measure corresponds to bitter compound levels in the beer. The higher the number, the more bitter.
Alpha Acid Units/Homebrew Bitterness Unit
Alpha acid levels change between crop years. When you find a recipe, you must adjust for your hops' different AA levels. Calculating IBUs on the fly is a math headache. To save brain cells, homebrewers devised the “alpha acid units” (AAU) or “homebrew bitterness unit” to scale hop additions of varying strengths. It does not calculate actual bitterness, just potential bitterness.
To find the AAU of an addition, multiply the weight by the AA percent.
AAU = Weight (hops) × AA percent (recipe)
To scale to your current hops, divide the AAU by the new AA percent.
Weight (needed) = AAU / AA percent (hops on hand)
For example: Your recipe uses a half ounce of 8.1 percent AA Cascade. You can buy them at 5.4 percent AA.
AAU = 0.5 × 8.1 = 4.05 AAU
Weight (needed) = 4.05 / 5.4 = 0.75 ounces
With these calculations in hand, you can quickly adjust.
Unless you have access to a spectrophotometer, your actual IBU levels remain a mystery. Small breweries often don't know the true IBU content of their beers. If you have access to a spectrophotometer, look to either the ASBC's methods by Rigby and Bethune or Moltke and Meilgaard.
Several formulas exist for IBU calculation, with different results. For brewers, calculating consistently with the same formula means more than the number. That way you know how 60 IBUs tastes for your system and calculations.
The Tinseth method of calculating IBUs starts with the AAU and a table of hop utilization. The utilization figure estimates how much bitterness you extract. The percentage decreases for whole hops and as the beer gets stronger and as the hops are boiled less. Higher gravities impede the isomerization process, so heartier beers need heartier doses of hops.
IBU (addition) = (AAU × Utilization percent × 7490) / Volume (beer)
Utilization factors can be found in Table C-1 in Appendix C. A constant to scale AAUs calculated by ounce weight is 7490.