What is dry hopping?
We all know that hops impart both a bitter taste and a wonderful aroma but these characteristics are contributed to beer by different components of the hop cone. The bitter flavour in beer is due to alpha acids which are present in the resin component of the lupulin glands found in the hop cone. The beautiful hop aroma however is due to a whole host of compounds present in the oil fraction in the lupulin glands. The problem in maintaining a full hop aroma in beer is down to the fact that, for a compound to be smelt it needs to be volatile. If you can imagine that an aroma compound present in a liquid needs to pass from the liquid to our nose for us to be able to smell it. Therefore the compound needs to move from being a liquid to being a gas. As such the more volatile a compound the easier this will occur and the easier that compound will be to smell. For a compound to be volatile it needs to have a low boiling point and this is where the problem with maintaining the hop aroma in beer comes from.
Brewers add hops to the wort boiling stage of the brewing process. They do this because the alpha acids in hops are not very bitter. For the alpha acids to become bitter their chemical structure needs to alter, or to use the more appropriate chemistry terminology, isomerised. The isomerisation of hops can be done with chemical agents but in the brewery it is achieved by the application of a lot of heat during the wort boiling phase. The better the boil the more isomerisation occurs and the better the yield from our hops will be. However, the down side of this is that by applying a lot of heat to the wort we are boiling off all those wonderful hop aroma compounds. To counteract this loss of hop aroma brewers will add aroma hops late in the boiling phase, usually in the last 5 or 10 minutes of boiling. By doing this the aroma hops are in contact with the hot wort for a shorter period of time and so less of the hop aroma is lost. This process is known as late hopping and I would guess that all of us as home brewers do this.
This practice is great and does deliver a certain level of hop aroma to the finished beer. However, dry hopping is a process where hops are added to the “cold” phase of the brewing process, which is fermentation and conditioning, to maintain as much fresh hop aroma in the finished beer as possible. By using the process of dry hopping brewers can achieve that really strong hit of hop aroma which many of us absolutely love.
Can home brewers dry hop their beer?
Dry hopping is certainly a technique that home brewers can employ. Certainly full grain and extract brewers can benefit hugely from using dry hopping. In fact I would argue that extract brewers could benefit the most as many liquid extracts are devoid of hop aroma due to the vacuum evaporation employed during their production.
How do you dry hop?
Dry hopping is very simple and there are a number of techniques that you can employ to achieve the desired result. You can use either whole hop cones or pellets, I have used both successfully and encountered no problems. The simplest way of dry hopping is to make a hop bag, a bit like a tea bag, from muslin cloth. You then put your hops into the bag and place directly into the fermenter. I tend to do this just after I have pitched my yeast and give the whole thing a good vigorous stir to allow the wort to fully penetrate the hop bag. As an alternative you can just add the hops directly into the fermenter without worrying about a hop bag. I prefer this technique as I feel you get better contact between the wort and hops allowing for more of the precious hop oils to mix in. However, the hop cones can clog up your siphon tube which can be a bit frustrating.
I am often asked what quantity of hops should be used for dry hopping and my answer is that there is no correct amount. Different hop varieties will impact on the hop aroma in different ways and hop cones behave differently to hop pellets. Furthermore brewers differ in their taste for hop aroma; one brewer’s beer hopped to perfection is another’s hop filled nightmare. Therefore for me the key is to experiment with different amounts until you hit on a quantity that best suits your personal tastes.
Finally there is the important issue of the microbiological stability of beer that has been dry hopped. Although as far as gram positive bacteria are concerned beer is protected by the anti-microbial properties of hops. But take added security from research that was carried out at the University of California at Davis which showed that dry hopping during fermentation or conditioning did not cause any microbiological problems.
Dry hopping is a technique that has been used by commercial brewers to great effect. Certainly the technique should be part of the home brewer’s toolkit if they want to create beers with a great fresh hop aroma.