Dry Hopping Techniques

Hops in a Pint Glass

Dry hopping is essentially a British (and now American) convention. With a couple of exceptions, it is not practiced by German, Bohemian or Belgian brewers.

What's the difference between dry hopping and late hopping? Well, for one, the aroma of a beer that has been dry hopped is preferred over that from a beer that is late hopped (where finishing hops are utilized for aroma). The aroma derived from late hopping is more intense and, since no boiling and thus less oxidation is involved, the aroma of the beer seems to more closely resemble that of the raw whole hops. The aroma imparted by dry hopping is likely to be more stable than when late hop additions are utilized.

As background, here is some basic information on hop utilization. The hops have two basic components: one is resins and the other is its essential oils. The resins are often called alpha acids and are isomerized (or changed) when boiled to yield iso-alpha-acids. It is these iso-alpha-acids which provide the bitterness in the finished beer. The essential oils in hops are responsible for the hoppy "nose" or aroma in the finished beer. These essential oils are very volatile and will be boiled off if they are added early in the boil. For most of the brewing world, aroma is attained by adding the hops late in the boil which allows the oils to be retained in the wort. Late hop additions usually occur from 10 minutes left in the boil to knock-out. For German brewers, they would just as soon not get any aromas from late additions. In fact, the typical flavors and aromas we think of as "Noble" are from early additions of bittering hops to the boil and never late hopping or dry hopping. If you tried to dry hop many German or Bohemian beers, the resulting flavors and aromas would most likely be out of character for the beer. It may be something you like personally, but I don't think the judges at a competition would agree.

There are basically three forms of dry hopping:

  • Adding hops to the primary.
  • Adding hops to the secondary.
  • And adding hops in the keg.
Adding hops at the beginning of fermentation in the primary is discouraged due to the loss of aroma as it is "gassed off" or "scrubbed" with the escaping CO2 formed during fermentation. However, many commercial brewers are more worried about the stability of their beers than slight losses of hopping efficiency. The more oxygen they can keep out of their beer, the more stable it becomes. So, rather than transfer to a secondary, they wait until the beer is almost through fermenting (maybe 4 or 5 gravity points left) and then add the dry hops. Any oxygen will be taken up by the yeast or scrubbed with remaining CO2, they don't have to worry about oxygen ingress into the beer due to transfer to secondary, and they still get plenty of time for the dry hops to work and settle out if added loose. This may be a method that homebrewers might like to try, especially on their beers which will be stored for long periods of time, such as Barley Wines or Old Ales, etc.

Most brewers dry hop in the secondary to get the highest amount of hop aroma for their buck. This is done for three reasons, sanitation, blowoff issues (hops plugging the blowoff tube), and to retain the most aromatics as possible. The problem, as mentioned above, is the possibility of oxidation problems and reduced shelf life down the road.

Dry hopping in the keg is often practiced, but some feel that the length of time the hops are exposed to the beer while in the keg gives it too much of a "grassy" or "oily" flavor. But, there are just as many who have never had any problems keeping hops in their kegs for up to four of five weeks. When using a corny keg, I like to use one of those stainless tea balls and a length of dental floss. The tea ball sinks to the bottom and the dental floss allows you to tie it all off on the outside of the keg but still maintain a good seal on the lid. A week is good when dry hopped warm, or up to three or four weeks when dry hopped at lager temps. Always let your taste buds be the final judge as to when it's time to pull out the hops.

Many homebrewers are worried about contamination issues from adding un-sterilized hops to finished beer. This is unlikely because when the dry hops are added, near the end of fermentation, the alcohol helps keep any possible contamination to a minimum. Plus, since there are not many sugars left in the beer, there is not much for the beasties to eat. And finally, hops are anti-microbial and are therefore are not a very good host for contaminants such as bactiera.

Which hops should be used for dry hopping? For the most part, aroma hops are those with low alpha acid content (less than 6%) and high essential oil content. The "noble" hops fall in this category as do most of the low alpha acid varieties. Some examples include Saaz, Tettnanger, Hallertauer, Goldings, Fuggles, Cascade and Williamette. As with most rules, there are exceptions. Many hops fall into the "dual use" category and have very good aromatic and flavor characteristics as well as good bittering properties. A couple of high alpha acid hops often used with good results for dry hopping are Chinook (12-14% alpha acid content) and Columbus (14-16% alpha acid content). It is usually best to use the regionally specific or traditional hop varieties for dry hopping as well as late hopping your beers. For example, most English beers are dry hopped with East Kent Goldings and most American beers are dry hopped with Cascade.

How much hops to use and for how long is a question often asked. A good rule of thumb for an average amount of aroma is one ounce of hops in 5 gallons of beer for 10 days to two weeks at between 60 and 70°F (16 to 21°C). For homebrewers who like a lot of hop aroma, try using 2 oz per 5 gallons for a moderate hop nose. For bigger beers, try as much as 4 oz per 5 gallons for that "in your face" aroma found in American IPA's or big pale ales. The real answer to the question of how much hops to use is, "as much as it takes to attain the desired outcome." More than 4 oz per 5 gallons may be pushing the upper limit some, but that is what we are famous for here in the US, pushing the limits of accepted practice.

In Britain, brewers typically dry hop for two to three weeks but a lower temperature, typically around 55 to 60°F (13 to 16°C). Commerical brewers in Britain use less hops when dry hopping in the keg, but do not remove the hops from the keg before serving, so it is exposed to the beer for a long period of time.

One alternative method to dry hopping is to make a hop tea. To do this you boil two cups of good brewing water, then remove from the heat and add your hops. Allow to cool and steep for an hour or two, then add the cooled tea to your beer. Adding a minute amount of acid, such as lactic or phosphoric acid, to the water will prevent it from leaching polyphenols from the hops which may cause astringency in the finished beer. Be careful when adjusting acid levels in such a small amount of water. Check it with a meter and stop when it is below 6 pH. Avoid pouring and splashing the tea into the beer. Any added oxygen will offset some of the effort by reducing the hop aroma through oxidation. Try siphoning with the end of the hose below the surface of the beer.

Lagers are generally not dry hopped but get their aromas from late hop additions, but when making a hop forward beer style (primarily ales), try dry hopping next time and see if you like the results.

Some Tips for Dry Hopping Success:

  • Before dry hopping in the secondary, rack off the trub in the primary to remove as much yeast mass as possible.
  • Try to keep your beer as cool as possible while dry hopping. In the low to mid 60's °F (16-20°C) is best.
  • Since we are now past the aerobic phase of fermentation, make sure to minimize the amount of oxidation to your beer. I like to put a layer of CO2 over the surface of my beers when doing any type of manipulation after the primary. And dry hopping definitely falls under the "manipulation" definition. We are not trying to keep oxygen from the beer per say, as much as we are trying to keep oxygen away from the hops. We definitely don't want to oxidize the hop compounds here. Better safe than sorry.
  • Just like you would before you rack from secondary to a serving keg, crash the vessel you are dry hopping in down to between 32-36° F (0°-2°C) to drop the hop mass and get as clear of a beer as possible.
  • You will get better extraction if you can stir the beer (without adding oxygen) to keep the hops in contact with more of the beer in your vessel.
  • To reduce the hop mass, you may want to use a hops bag, especially if you are dry hopping with pellet hops.

References: Information for this article was adapted from the Brew Your Own Magazine article by Donald Million entitled Dry Hopping: Techniques online date of August 26, 2003, the book Homebrewing: Volume 1 Beginner Basics to Creating Your Own Award-Winning Recipes, by Al Korzonas, the paper in Chem. Educator 2000 entitled Beer: An Ancient Yet Modern Biotechnology written by Charles Bamforth, Department of Food Science and Technology , UC Davis and for the dry hopping tips, Brewing Better Beer: master lessons for advanced homebrewers written by Gordon Strong.

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