Hops impart different characteristics to beer. Knowing when, and how, to add hops to the brew gives the home brewer great scope for variety.
Hops contain several classes of chemical compounds. Brewers are interested in two broad groups: resins that add bitterness, and essential oils that add flavour and aroma.
The resinous bittering compounds are known as alpha-acids. Not normally water-soluble, these chemicals require the brewer to boil the hops vigorously for an hour, at least. This causes the chemical structure to subtly change, or “isomerise” into compounds that are water soluble and more bitter.
The essential oils, responsible for flavour and aroma, are more volatile than the alpha-acids. The act of boiling hops for an extended period evaporates these chemicals. So flavour and aroma hops must be added at later brewing stages to avoid this fate.
As such, most home brewing recipes call for hops to be added to the brew at different times, depending on their purpose.
Adding Hops to the Boil
A simple rule of thumb for most beer brewing is to add hops at three stages:
- Bittering hops: Start of boil
- Flavouring hops: After 40-60 minutes
- Aroma hops: After another 10-20 minutes, for 0-5 minutes before turning off the flame
The advantage of this approach is its simplicity. The disadvantage is that certain hop aromas will always evaporate from hot wort, at any stage of the boil.
So the home brewer needs to consider ways of minimising the evaporation, or adding hops once the wort has cooled. A word of caution: while simply putting a lid on the boiler may prevent some evaporation, it may also result in the wort boiling over onto the cook surface.
This technique involves putting fresh hop flowers in a closed vessel attached to the boiler outlet pipe. The hot wort then passes through this vessel, picking up the hop volatiles as would hot water through tea leaves. The enclosed fittings prevent the volatile hop oils from escaping.
There are drawbacks, however. The construction of a hop-back, and pipe & tap connections will require materials able to withstand near-boiling wort, and be air-tight. Another concern is the cooling of the wort once it has passed through the hop-back. The inclusion of another in-line fitting, such as a counterflow chiller, will cool the wort effectively. This, however, is a more advanced brewing technique.
Adding Hops to the Fermenter
Another way to conserve the volatile hop aromas is to add hops to the cooled wort. Many home brewers, and professional brewers for that matter, will add hop flowers to the fermenter. Over the course of the brew, a good amount of hop aroma will be taken up by the fermenting beer.
However, this technique is not perfect either. Beer fermentation is an active process, with the yeast generating a lot of carbon dioxide which bubbles up and out of the airlock. This has the effect of “scrubbing” some of the hop aromas from the beer.
Adding Hops to the Beer
Once primary fermentation has finished, hops can be added at any stage until serving. Many home brewers add hops to the secondary fermenter. This allows a week or two of hop oil absorption into the near-finished beer, while nothing is lost through evaporation.
After bottling or kegging, some brewers will salvage the hops, and use for bittering in a subsequent brew. Of course, these hops will no longer have their aroma oils.
Another approach, similar to the hop-back, is to add an in-line hop vessel through which beer passes before reaching the tap. The best example of this technique is the “Randall”, pioneered and popularised by the Dogfish Head brewery of Delaware. A three-foot glass vessel is packed with hop flowers, and imparts fresh, vibrant flavours to the beer just prior to serving. It also makes an attractive addition to a brewpub’s serving area. Again, this is an expensive and advanced brewing technique, but one that has been adopted by enthusiastic home brewers around the world.