Wet Hopping is the process of using un-kilned, hence “wet,” hops in brewing. In the Northern Hemisphere, aroma hops are typically harvested in late August and early September and high alpha-acid hops used for mostly bittering are typically harvested in mid to late September. Wet hops are approximately 80% moisture and this is reduced in a hop kiln right after the harvest to about 9%. Getting the hops dried correctly is critical. If left too dry, hops may oxidize, and there is the heightened risk of warehouse fires. If left too wet, baled hops may “sweat,” become moldy, and develop off aromas. When brewers use hops wet, therefore, they must be loosely packed in cardboard boxes right after picking and shipped via the fastest method straight to the brewery, where they are used immediately. If they aren’t used right away, the hops will deteriorate quickly, becoming unusable for use in wort or beer.
Beers produced with un-kilned hops are referred to as “wet hop” beers, “fresh hop” beers, “green hop” beers, or “harvest” beers. These beers have emerged largely in the past 10 years and are almost exclusively produced by American craft brewers located in hop-growing areas. Because of the high moisture content of wet hops, brewers typically use at least four to five times the weight of wet hops as they would of the same variety in its kiln-dried state. Wet hops, just like kilned hops, can be added at any point in the boil, or into a hop-back. Adding wet hops to cool, finished beer is also gaining in popularity. The reason behind such “wet dry hopping” is the desire to capture the hops’ most delicate and volatile aroma oils in the finished beer. Like traditional dry hopping, “wet dry hopping” captures volatiles driven off during a kettle boil but also those that may be driven off by the hop kilning process. Some beer enthusiasts enjoy the uniquely “green” delicate character of these beers, while others are put off by the distinctly grassy chlorophyll-like aromatics. Regardless, these beers are very unique creations driven by a particular time and place, and therefore represent a fascinating evolution of the brewer’s art.