By Greig McGill
Dry hopping. There’s so much talk about it, and it’s practically de rigueur these days for any hoppy style of beer to be at least dry hopped once, with double dry hopping, and even triple dry hopping becoming more and more of “a thing” in the craft beer arms race for hype and dollars. Does it matter though? What’s the best way to dry hop? And why do we do it at all? Well, grab yourself a pint of something (dry) hoppy, sit back, and I’ll have a rough crack at trying to explain.
Historical Roots and Evolution of Dry Hopping
The practice of dry hopping can be traced back centuries, with historical records suggesting its use in traditional British ales. Brewers in the 18th and 19th centuries (as early as 1700, according to British beer historian Ron Pattinson) discovered that adding hops directly to casks during the maturation phase enhanced the beer's aroma without intensifying its bitterness. They were also used for their “freshening” power - effectively the hops triggering some extended fermentation activity. Today we call this phenomenon by the less positive sounding name of hop-creep. Over time, this method evolved, and dry hopping became a well-established technique in both traditional and contemporary brewing. For the dedicated historian, the aforementioned Mr. Pattinson has a trilogy of historicalposts discussing the original paper from 1893 talking about the freshening power of hops.
Types of Hops and Their Characteristics
The choice of hops is critical in dry hopping, as different varieties contribute distinct aromas and flavours to the beer. The aromatic compounds responsible for these sensory experiences are found in lupulin glands - the small yellow glands located in the hop cone, and my favourite source of sticky hands during hop handling! The main hop varieties used in dry hopping include:
1. Citrus Hops (e.g., Cascade, Centennial): These hops impart bright, citrusy aromas such as grapefruit and orange. They are popular choices for dry hopping in pale ales and IPAs, particularly the older West Coast type styles, adding a refreshing and zesty character.
2. Floral Hops (e.g., Saaz, East Kent Goldings): Known for their floral and herbal notes, these hops contribute a delicate and perfumy aroma. They are often used in lagers and traditional English ales.
3. Tropical Hops (e.g., Nectaron, Mosaic): These hops bring tropical fruit aromas like pineapple, passion fruit, and mango to the beer. They are frequently used in modern hop-forward styles, enhancing the beer's fruity and exotic profile.
4. Spicy Hops (e.g., Styrian Goldings, Tettnanger): Hops with spicy and earthy characteristics are employed to add depth and complexity to the beer. They are commonly found in Belgian ales and certain traditional German styles.
Note that these are not strict categories, and some hops, such as Citra, may overlap - in that case, having both citrus and tropical notes. There are also newer hops such as the Neomexicanus-derived breeds. Sabro is one of these, and is known for coconut (!) aromas as well as tropical notes.
Understanding the flavour and aroma profiles of different hop varieties allows brewers to craft a beer with a specific sensory experience in mind.
Dry Hopping Techniques
Single Dry Hopping
This is the “standard” method of dry hopping, whereby hops are added once to the fermenting/fermented beer, either “just thrown in”, or transferred in by one of several, sometimes proprietary methods. Temperature, amount of contact time, recirculation, and other factors are often unique to each brewery, and opinions are hotly divided among what is the “best” process. I’ll talk more about that later. After the desired contact time has been reached, the hops are usually removed from the beer (with varying levels of efficiency).
Double Dry Hopping
Exactly as above… except performed twice! Sometimes with removal of the first lot of hops, sometimes in addition to them. Again, opinions are divided and verbal battles fought over the “best” technique. I’ll leave you to guess what triple dry hopping might be as I’m sure you get the picture!
Hop Bursting
Not really dry hopping, but often a precursor to it, where huge quantities of hops are added to the (usually slightly cooled to less than 75 degrees Celsius) wort during the whirlpool. These hops are usually left in the kettle before pumping to the fermentation vessel, but I am aware of at least one brewery that pumps all that hop matter across and leaves it in during fermentation.
Hop Stand
Also not really dry hopping, but a pre-fermentation precursor, and very similar to Hop Bursting above. A large charge of hops are added to the wort after flameout, and allowed to sit. This does add some bitterness, but also avoids volatilisation of too many of the delicate aroma compounds that are driven off in the boil.
Dip Hopping
The new-ish kid on the block. This is a hybrid of hop bursting and dry hopping. It involves adding hops to the fermenter, and running in some wort to mix the hops thoroughly, standing for a while before completing the wort transfer. The original development of this technique was way back in 2012 by employees of Japan’s giant Kirin brewery, but it’s taken a while to catch on. The Japanese team used hot wort for the “dip”. Others, myself included, have tried this technique but with cold wort, and I certainly believe there’s something to it. In my own tests, I have achieved a similar effect to a 10g/L dry hop with a 5g/L dip hop. I then dry hopped on top of it because I’m an animal.
Impact on Beer Characteristics
Aroma
As mentioned before, hopping during the boil or even in the whirlpool can have the effect of destroying the delicate hop aromas that most of us enjoy so much in our beer. Dry hopping - adding hop cones, pellets, or other forms of processed hops to our beer is a way of capturing all of that nuance that would otherwise be lost to the steam!
Flavour
As well as the aromatic compounds leading to similar flavour expression - most of what we taste is actually smell - there are certain flavours that are perceived from some (or too much) dry hop. These range from a pleasant grassiness, to a full-on resinous flavour, and even to unpleasant cheesy or vegetal notes depending on hop age, quality, and dry hop technique, particularly contact time.
Appearance
If you are filtering your beer, or have an excellent fining regime, dry hopping won’t have much, if any, impact on the clarity of your beer. If not though, dry hops can remain suspended causing a light dry hop haze. They can also create haze when their polyphenol compounds bond with proteins in the wort from the grains. This form of haze is very stable and often desired in modern “hazy” styles of beer. Finally, hop resins are foam positive, and can really contribute to a beautiful pillowy head. I have found that dip hopping in particular seems to promote this, but this is my own anecdotal finding only and not to be taken as science!
Challenges in Dry Hopping
While dry hopping is a powerful tool for brewers, it presents some challenges
Oxygen
Oxygen exposure is probably the most common reason why brewers are wary of dry hopping, and many techniques have been invented to minimise or prevent it. Commercial brewers have a variety of methods for minimising this, and the simplest is just to ensure the vessel is under slight positive pressure via a very light CO2 feed before throwing the hops in. This is often followed by bubbling CO2 through from the bottom of the tank and “burping” the top to help mix the hops as well as to drive off any oxygen introduced. Others just trust in the yeast still present to scrub any O2 ingress, and I’d suggest care, along with the latter approach to concerned homebrewers. Add the hops as quickly as you can with as little time for oxygen to mix and dissolve, and get the airlock back in place ASAP.
Timing, Temperature, and Technique
Ask ten brewers how they dry hop and you will likely get ten different answers. Leaving out gizmos like hop rockets, torpedoes, and pump recirculation for minimal contact time with maximum contact area, the variation really involves the three Ts. When, and for how long do you dry hop? At what temperature (or range) do you dry hop? And how do you physically get the hops in and out again? I’ll leave out the last one, as it’s usually tied to your particular setup. For example, at Brewaucracy, I only really have two “easy” options. I could make a hop slurry and pump them in from the bottom (probably introducing way too much oxygen) or I can climb my trusty ladder and pour them in from the top (while under positive pressure as described above). Getting them out involves dumping from the cone, and can be an absolute nightmare of lost beer, or clogged up valves with higher dry hopped beers.Timing has historically been the most contentious and divisive factor. Some brewers swear by adding the hops early in fermentation, especially the haze-loving brewers, as it was claimed that this helps with biotransformation, and those “juicy” flavours, as well as stable haze formation. Newer studies have suggested1 that this isn’t true though, and neither factor is increased by an early addition. It’s also been shown that haze can actually be reduced by this method. Personally, I like to dry hop when I’m around 4-6 points from projected terminal gravity. This helps to minimise hop creep while the fermentation isn’t active enough to drive off the delicate aromas. I also do a fairly typical 72 hour dry hop contact time.
Some brewers prefer long and cold, others short and warm, and everything in between. Warm versus cold really comes down to which flavours and aromas you want in your final beer, as the temperature impacts this, but the cooler you dry hop, the longer you will need to extract the compounds you like, risking vegetal and grassy character. I think around 2-3 days at roughly 18-20C is a good compromise.
1 Apologies, you’ll need a log-in for that article, but I present it by way of citation.
Consistency
Hops, being an agricultural product, change annually. From the amount of alpha and beta acids, to the quantity and proportional makeup of the various oils, the properties of this year’s Nelson Sauvin will simply not be the properties of next year’s Nelson Sauvin. And that’s without getting into the fact that different farms, or even different rows on the same farm will produce differing hop qualities. The art of smelling and blending is very important if consistency is a goal, but I prefer to just “let craft be craft”, and not mind that each batch will be slightly different. Storage of your hops is also important. If you can, flush your opened left over hops with CO2 and seal them in an airtight container after use. Keep them as cold as possible - in the freezer is ideal, but below 4 degrees Celsius is a minimum. Oxygen and warmth will speed up the degradation of the delicate hop oils.
Conclusion
Hopefully you now have a deeper understanding of your options when it comes to dry hopping. It’s not always just about “more is better”, and we’re only now just beginning to understand which compounds are extracted, transformed, and expressed and at which temperature, over how much time. While this knowledge will evolve, the reality of how you choose to dry hop will always depend on your tastes and your tastes alone. With the methods I’ve outlined here, and always listening to your own palate, you have the tools to truly do it your way while avoiding the negative factors. But hey, if you like a really grassy, slightly vegetal character in your beer, well, rules are made to be at least bent!
Go forth, and dry hop like beasts!