Maximizing Hop Flavor and Aroma - The Process of Hop Addition
bittering additions
As we mentioned earlier, big bittering additions aren’t going to get us to our flavour and aroma goal. The essential oils in hops are extremely volatile, and a 60 to 90-minute boil will drive off just about everything that we want. Depending on what we’re brewing, for our bittering addition we usually select a hop with a high alpha acid content so that it doesn’t take much to achieve the bitterness we desire.
intermediate additions
This addition, added with anywhere from 30-10 minutes remaining in the boil, is frequently referred to as a “flavour” addition in recipes; fortunately, many brewers are coming to realize that if they really want flavour, it’s best to skip this addition altogether. It’s counterproductive to add hops for flavour only to have half of the flavour compounds boil off. Studies have shown that an alcohol like linalool, which contributes fruity and floral elements, can be reduced by as much as 50% in as little as 5 minutes of boil time. We’ve taken this information pretty seriously, and seldom waste our hops on the so-called “flavour addition.”
post-boil additons
Since flavour compounds are so volatile, it makes sense to find temperatures that will extract those compounds and make them soluble, while not driving them off. Whirlpool and steep additions have become the standard means of achieving that. Flavour tests have confirmed that steep additions account for far and away the most flavour; they also contribute a significant amount of aroma. Dry hopping, on the other hand, contributes almost exclusively to aroma, at least positively; vegetal and grassy flavours can result from lengthy dry hopping.
Two main concerns remain then for whirlpool or steep additions: temperature and time. We’ve read brewers advocating everything from 96°C down to 60°C (205°F to 140°F). To date, researchers have identified aroma compounds numbering in the mid-400s. Some of these are incredibly delicate and disappear very quickly, while others need heat and time to become soluble in wort. Add to this equation the growing variety of hops, and it becomes clear that a lot of experimentation is required – lucky for us!
In our experience, we’ve had the best results by reducing our temperature to 80°C - 77°C (175°F - 170°F). Typically, we fill the BIAC chilling jacket once and then shut the water off. Depending on ground water temperature, one jacket full gets us pretty close to our steep temperature. This will obviously require some individual experimentation, just be aware that the high-end temperatures come off really quickly, and it’s easy to overshoot and drop too low. It’s also worth mentioning that at this stage, oxygen pick-up can lead to off flavours. Thiols from the hops combined with oxygen can lead to a perceptible green onion profile, so be careful trying to stir temperature out. Once we hit our target temperature, we add our steep hops. This is by far our largest addition and we let these soak for 50-60 minutes with occasional gentle stirring.
dry hop additions
At this stage, take any possible steps to mitigate oxygen exposure. Oxygen is definitely the enemy once the bulk of fermentation has taken place. One of the ways we limit exposure is through a single dry hop addition. As well, we try to time our addition to serve several functions. We dry hop at the same time we perform our diacetyl rest. With a few gravity points left, we begin to raise the temperature incrementally. By adding our dry hop at the beginning of this process, we also help to eliminate the risk of “hop creep” caused by enzymes in the hops converting normally unfermentable sugars to fermentable ones. Because fermentation is still happening, the production and presence of CO2 helps prevent oxidation. Some brewers are experimenting with adding hops much earlier in fermentation to benefit from “biotransformation”; however, there are far more essential oils present from the whirlpool or steep hops than from dry hop additions, and biotransformation will be taking place regardless of when dry hops are added.
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