Ask Mr. Wizard

Freezing Fresh Hops


Sten Regild - Copenhagen, Denmark asks,

What happens when you freeze freshly harvested hops without drying them first? I have been doing this for the last couple of years with part of my hop harvest and then I use 3.25 times more of the frozen wet hops than calculations tell me to use of dried hops for a certain IBU level. I have been homebrewing for 44 years and taste-wise I can’t tell which beer has been made with frozen wet hops. I can understand that frozen wet hops is not a good idea for the industry, but for homebrewers it can make life much easier.


This is a really interesting question about hop storage. Brewers can, at times, be skeptical about observations reported by newer brewers, especially when the observations have to do with changes in flavor. Right or wrong, that’s just the way it is. After 44 years of homebrewing, you are a bona fide old-timer, and I believe your observation when you state that you are not tasting a difference between beers brewed with dried and frozen hops. Now, the skeptical scientist-side of me could ask if you are basing your conclusions on controlled experiments and proper sensory panels, but you get a pass because you come from Copenhagen, the home of one of the most influential brewing science labs in the history of modern brewing!

Hops are typically kiln-dried after harvest and compressed into bales to extend shelf life, reduce storage volume, decrease shipping weight, and make handling during brewing easier. The primary benefit of the hop bale is the minimization of oxygen. However, drying and compressing hops is only part of the hop storage equation; temperature is the other key storage factor, and the cold storage of hop bales is vital to this whole process. Most brewers these days use hop pellets and/or liquid hop extracts in the brewing process because these preparations are much easier to handle and have longer shelf lives than hop bales, but both types of hop products begin as bales.

As you point out, storage volume and shipping weight are really non-factors for the homebrewer who grows their own hops. So simply freezing homegrown hops seems like a good choice. I did some research about this topic and could not find anything specifically related to freezing green hops, so I did some reading about freezing vegetables and about hop quality loss during storage. The two stand-out topics to my eye are oxygen and enzymes.

Oxidation is the main enemy of hop quality during storage, so anything that you can do at home to minimize oxygen is a benefit. Vacuum sealers are the obvious choice, but can be a bit pricy. Freezer bags coupled with squeezing and sealing can make a decent substitute for vacuum sealers. But no matter how much hops are compressed, there will always be some amount of oxygen.

The other stand-out topic related to hop storage is enzymatic degradation. Food scientists have extensively studied this topic because of its relevance to all frozen foods. Clarence Birdseye is recognized as the father of commercial food freezing; the first commercially frozen meat, seafood, and vegetable products sold using Birdseye’s patented processes were sold in 1930 and had a quick and profound effect on commercial food processing. One of the interesting things about frozen fruits and vegetables is that enzymatic reactions slowly continue during frozen storage.

The blanching process is often used to denature fruit and vegetable enzymes before canning or freezing to prevent enzymatic browning; in the case of frozen fruits and vegetables, blanching slows or halts (depending on the process) enzymatic activity during frozen storage. Hop kilning reduces the moisture content of hops, and it also denatures enzymes. Based on what is known about enzymatic activity in fresh-frozen fruits and vegetables (no blanching used), it is reasonable to assume that enzymatic reactions occur in fresh-frozen hops.

You have been successfully using fresh frozen hops for the past couple of years, so if you are happy with the results you should continue what you have been doing. Minimizing the oxygen content, reducing the freezer temperature as much as possible, and minimizing storage time are three things that you probably should be mindful of with these hops. Blanching (short exposure to steam) your homegrown hops is something you may want to consider if you are interested in further developing your freezing process. Skill!



Response by Ashton Lewis.