As discussed in the first installment of this article, substituting a lesser weight of higher alpha hops for a higher weight of lower alpha hops is one way to tweak the hop profile of your beer. In that case, you could achieve the same IBU rating, but with less plant material added to your kettle. This decreases the volume of beer lost to trub and hop debris in the bottom of the kettle. And, in the case of very hoppy beers, may lower the amount of astringency contributed by the hops (because hops contain tannins as most plant material does). There are also ways to tweak your late hop profile to get more “bang for your buck” from your hops.
Alpha Acids and Oils
Hops contain alpha acids. In brewing, the hops are boiled to extract and isomerize these alpha acids. This creates iso-alpha acids which are the primary source of bitterness in ordinary hopped brews. The longer hops are boiled, the more alpha acids are isomerized. However, the rate of isomerization slows over time. So, in most cases, bittering hops are boiled for 60–90 minutes, with 60 minutes being very common in homebrew recipes.
Hops also contain essential oils, such as myrcene, humulene, caryophyllene, farnescene, and others. These oils are volatile and are extracted quickly from the hops. Further boiling just causes them to evaporate.
Armed with the knowledge above, many brewers practice what might be called “bookend hopping” — they make one hop addition for bittering, then one hop addition late in the boil, often at knockout. The idea is that the bittering hop addition yields as much alpha acids as is practical and the late or knockout addition is strictly for aroma. Adding hops in the middle of the boil yields less bitterness and less hop aroma. In fact, there’s a “vomit zone” in the early middle of the boil where few alpha acids are extracted, but most of the oils have already evaporated. So, having two hop additions bracketing the boil give the highest levels of alpha acids and oils by adding the least amount of hops.
Multiple Hop Additions
Of course, other brewers do precisely the opposite and add at various times during the boil, including adding hops continually through the boil. To reach the same level of iso-alpha acids and essential oils in the wort, more hops are required.
It’s logical to ask which method is better. However, that’s a value judgement, not something that can be measured. “Bookending” saves brewers a little money on hops, and — in very hoppy beers — dials back on the astringency a bit. But, many tasty beers are brewed with hop additions in the middle of the boil, where few alpha acids are extracted and yet most of the oils get boiled off.
If you have the time, and want to tweak your favorite IPA recipe, exploring a couple different hopping schedules is worthwhile. When you do, take note of everything. Of course you’ll want to compare the quality of the hop bitterness and aroma. But also examine things such as clarity, foam, and astringency. In addition, forget all the details that went into the beers and pick the one that speaks to you. You may, for example, enjoy a little astringency in your IPA. For whatever it’s worth, I think that a hint of “roughness” in a very hoppy IPA can be a good thing. But, I also know that a smoothly bitter IPA can be a great thing, too. In the end, your goal is to make a great beer, not maximize numbers on a spreadsheet. And, not everything is known about hops. Maybe adding hops during the middle of the boil doesn’t make sense in terms of alpha acids and oils, but there may be some other reason for adding them. So always let your taste be the final judge when tweaking your beers.
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