Dry hopping is the process of adding hops to the primary fermenter, during conditioning, or the cask-conditioned ales to increase the aroma and hop character of the finished beer. Dry hopping greatly enhances hop aroma and flavor, especially when the hops are added after most of the fermentation process is complete, minimizing loss of aroma in the carbon dioxide. Dry hopping adds no bitterness to the beer, and any lingering bitterness will dissipate in a few weeks. This is because alpha acids are only slightly soluble in cold beer. It should also be mentioned that a beer that has been dry hopped is also usually late hopped in the kettle. Some brewers believe dry hopping should not be done during primary fermentation because of the risk of contaminating the beer with microorganisms.
Whole Hops or Pellets
Brewers can use whole hops for dry hopping but there are two potential problems in using whole hops. First, the whole cone hops contain oxygen which require they be flushed with carbon dioxide, nitrogen, or sterile water before adding to the fermenter.
The main challenge of hops introduction is conveying the material into the system without excess oxygen pick-up. Oxygenation negatively affects the chemical reactions that lead to the integration of the essential oils into the beer. To achieve a consistent aroma integration, it is important to prevent oxygen from coming in contact with the product. Typical methods for hops introduction include the following:
During dry hopping, enzymes associated with the hops begin breaking down unfermentable dextrins left behind after primary fermentation into fermentable sugars. In the presence of live yeast, the newly present fermentable sugars can lead to an over-attenuation of the beer, which is commonly referred to by brewers as “hop creep.” Over-attenuation is when beer ferments too aggressively.
Impact of Hop Creep
This over-attenuation can result in higher alcohol and lower residual sugar contents in the packaged product. If beers are dry-hopped after fermentation is complete, hop creep can cause yeast to leave dormancy, yielding higher amounts of yeast-related off-flavors such as diacetyl and acetaldehyde.
Conditions Influencing Hop Creep
Hop creep requires three conditions for it to appear: (1) some amount of unfermentable real extract in the wort or beer prior to dry-hopping; (2) live yeast in suspension; and (3) the addition of hops to fermenting or fermented beer. The longer the hops are in contact with the beer, the more their enzymes will break down the dextrins left behind by primary fermentation.
Prevention of Hop Creep
There are different philosophies around dealing with hop creep. A recent technical brief published by the Brewers Association suggested modifying beer recipes to create a more fermentable wort that is less susceptible to hop creep. Dry-hopping at lower temperatures and after fermentation a total or partial centrifugation will reduce the extent of hop creep and potentially limit the secondary diacetyl spike, but it will not eliminate it completely.
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