The Secret to Big Hop Aroma and Flavor

I wrote the bones of this article years ago, not long after a pint of Evil Dead Red with Peter Zien made me rethink most of what I thought I knew about hops. The central idea (that you can shift your whole hop load late and get huge, smooth flavor and aroma) has only gotten more true in the years since. But we have learned an enormous amount about what is actually happening in the kettle, the whirlpool, and the fermenter, and a few things we used to say with real confidence turned out to be incomplete. So this is the original piece brought up to date, with the old advice intact and a good deal of new knowledge layered on top.

Have you recently come across a craft brew with a massive hop flavor and a smooth bitterness that you really loved? If you're like me, you wondered how the brewery created such an incredibly huge, but smooth, hop character. The secret, it turns out, is very large additions of late hops, though late hopping is now just the front door to a much bigger house.

Late hopping is the addition of hops during the latter part of the boil. It is an excellent method for creating hop aroma and flavor in your beer. In general, any additions with less than 30 minutes left in the boil and prior to cooling the wort are considered late hop additions. Although some hop oils are lost during this shorter boil, reactions between the hop compounds and the wort create other desirable flavor-active compounds not found in hops.

Many brewers turn to dry hopping in an effort to get more hop flavor and aroma, and dry hopping does result in a different hop character than boiled or whirlpool hops. While boiled hops have long been characterized as more floral and spicy, Ray Daniels, in Designing Great Beers, noted that late-boil additions tend to read as more floral and fragrant, and less grassy, than dry-hopped ones. That was the conventional wisdom when I first wrote this, and there's truth in it. But it sells dry hopping short by today's standards. We now know that a great deal of what makes a modern hop-forward beer sing (the tropical, juicy, vivid aromas that the old floral-and-spicy vocabulary can't quite reach) comes from dry hopping, and specifically from what the yeast does with those dry hops. Kettle, whirlpool, and dry hop are not competitors; they are three different tools, and the best hoppy beers use all three deliberately. More on the dry-hop side of this later.

Lots of late hops = lots of flavor and aroma

It seems really simple when you think about it: add more late hops and get more flavor and aroma. Most of us, when we started brewing, were told that early hop additions are for bittering only and late additions are for flavor and aroma only. What we were not told is that shifting the bittering load to late in the boil can still provide substantial bittering in addition to a huge hop flavor and aroma. Done right, it can produce some really spectacular results.

While the great brewing scientist Jean de Clerck found late hopping to be wasteful and possibly harmful to beer flavor, professional brewers today are turning more and more to late hopping to get the big hop aroma and flavor that consumers crave. Sure, it costs more, but many brewers find their customers appreciate the results.

I first learned how far some brewers were pushing late hopping while drinking a pint of AleSmith's Evil Dead Red with owner/brewer Peter Zien. This Halloween seasonal ale has substantial malt character, smooth bitterness, luscious mouthfeel, and an almost blood-red color. Yet what really made me take notice was the amazing hop flavor and aroma that is enjoyable from start to finish. When I asked Zien how he got that profile, he replied, "Except for 3 or 4 IBUs, we add all of the hops during the last 10 minutes of the boil." At that time I had never heard of, nor tasted, anything like that, and I was intrigued.

The beauty of this beer is how the components of malt and hops exert themselves separately and substantially, rather than working to balance each other. The trick lies in a heavy load of late hopping, creating a big flavor and aroma profile with only a minimum of up-front hop bitterness. This allows the malt character to remain strong and perceptible even in the face of big hop flavors and aromas.

— Peter Zien, AleSmith

Another brewery that has embraced late hopping is Firestone Walker Brewing Company of Paso Robles, California. Brewmaster Matt Brynildson says, "We practice a lot of late hopping on the majority of our beers. Our main goal with increasing our late hops is big hop aroma and flavor. All of our beers have at least some hops added at the beginning of boil for bitterness, as this also helps to keep foaming and boil over down in the kettle, but these kettle charges are minimal to allow for larger late hopping charges."

Brynildson goes on: "American craft brewers practice a number of different methods of late hopping, with one very popular method being whirlpool hopping. Adding hops late in the whirlpool results in lower isomerization of alpha acids and good uptake of hop oils and flavor components, especially with pellet hops. The fact that there is some isomerization (about 15% in the whirlpool versus 35% in the kettle) means that not only hop aroma and flavor can be achieved, but also some bittering."

Having found out about the increased use of late hops at some of my favorite breweries, I began experimenting myself and encouraged a number of experienced homebrewers to try it. Longtime homebrewer David Sousa brewed an IPA with Columbus hops, all at 15 minutes or later. "The results were as expected and more," he said. "The hop flavor was huge. Another thing I noticed was an increased mouthfeel. The beer had a really nice texture in addition to a very clean hop flavor. And it doesn't make you feel like you need to wait before you take another sip. Dry hopping, by comparison, tends to cling to the palate a bit more."

Sousa's comment on mouthfeel echoed my results and the results of another highly technical homebrewer, Scott Lothamer. Lothamer made a Classic American Pilsner with hop additions at 20, 10, 5, and 1 minute. The result was a huge hop flavor and, compared to another of the same terminal gravity, significantly more mouthfeel. That beer went on to win Best of Show at a homebrew festival the following week.

A word of caution from John Palmer in How to Brew: depending on amount, variety, and freshness, beer hopped at knockout or via a hopback may take on a grassy taste from tannins and other compounds usually neutralized by the boil. I asked Zien and Brynildson about negative effects. Zien said AleSmith hasn't run into any with abundant late hopping; critical factors appear to be fresh, low-cohumulone hops, softened water, and original gravities above 1.055. A lower-gravity beer might show grassiness or astringency with severe late hopping, since the malt can't balance it. Brynildson said the downsides are mostly yield and efficiency: low utilization, lower whirlpool yields, possibly plugging the heat exchanger, "but the bottom line is that it is worth it because it makes excellent beer!"

What about bittering?

Adding more late hops will also increase the bitterness of the beer, so you'll need to reduce the bittering additions to land at the same overall IBU level. When AleSmith brews beers like Evil Dead Red, they get most of the bittering from the late hops, which allows for the maximum late-hop charge and a huge hop flavor.

Moving hops late not only reinforces the flavor and aroma, but some brewers suggest it produces a smoother, less harsh bitterness. Greg Noonan, in New Brewing Lager Beer, writes that beers heavily hopped at the beginning of the boil are more stable but the bitterness is coarser and less pleasant. Several homebrewers have reported a more rounded, less angular bitterness after switching a recipe to all late hops. That said, Brynildson cautions there's no definitive proof of harsher bitterness from early hopping, so the smoother perception may be partly expectation.

Hop selection

Select late hop varieties based on how pleasing the aroma is. Brynildson uses low-alpha aroma varieties and mid-alpha dual-purpose hops: Styrian Golding, East Kent Golding, Cascade, Centennial, Crystal, Mount Hood, US Fuggle. Zien looks for aromatic varieties with good flavor and low cohumulone: Cascade, Amarillo, Tomahawk, Simcoe, Chinook, and Palisade, with the higher-alpha ones used in lesser percentages. Some studies suggest high-cohumulone hops give harsher bitterness, but Brynildson doesn't buy the cohumulone-equals-harsh theory and plans to keep using great-smelling high-cohumulone hops. That skepticism has aged well; the cohumulone-equals-harsh idea has largely fallen out of favor. The practical takeaway hasn't changed: choose late hops for flavor and aroma first, cohumulone second.

What has changed is the palette. When I first wrote this, Cascade and Amarillo were about as exotic as it got. Today the aromatic, fruit-forward varieties that define modern hoppy beer (Citra, Mosaic, Galaxy, Nelson Sauvin, Sabro, Strata, Idaho 7, and others) are easy to get, and they push aromas the old floral-and-spicy hops simply don't have: passionfruit, mango, citrus, wine grape, even coconut. I urge you to smell and taste before you commit. Rub a few pellets between your palms, warm them, and see what they actually give you, because lot-to-lot variation in these varieties is real and a great-smelling lot is worth more than the name on the bag. It is also worth knowing about concentrated lupulin products: Cryo Hops and similar LupuLN2-style pellets, made by cryogenically separating the lupulin from the leaf. You get roughly twice the oil and alpha for the weight, with the green, vegetal bract material removed, which means less grassiness and far less wort lost to a soggy hop mass. For huge late and dry-hop charges, where leaf and ordinary pellets can soak up gallons of beer, that last point alone can make them worth it.

Pellet or whole leaf? The majority of brewers I spoke with use pellets for this technique. They break up quickly and expose the alpha acids for isomerization. Whole hops can be used with a false bottom, but the large mass makes it harder to extract the wort at the end of the boil. Brynildson: "I would always select pellets for late/whirlpool hopping."

Calculating the numbers

To use this in your own beers, replace all or part of your traditional bittering additions with additions at 20 minutes or less, increasing the amount to reach the same IBUs. Replace all of your bittering hops for an intense hop flavor; replace less to just enhance it.

Utilization isn't linear across the boil, so you don't need six times as much hops for a 10-minute boil as for 60. Assuming about 30% utilization at 60 minutes, you'll get around 17% at 20 minutes, 14% at 15, and around 10% at 10, so roughly double or triple the hops for equivalent bitterness. Use whatever software or method you already use. Most formulas are less reliable for very late additions, but don't let that stop you: a 5-IBU difference is hard to detect in a moderately bittered beer and impossible in a highly bittered one. In beers above ~50 IBU you may still want a charge of high-alpha hops early so the flavor doesn't overwhelm.

Two modern cautions on the numbers. First, once you move hops into a temperature-controlled whirlpool below boiling, the usual utilization formulas fall apart almost completely. Isomerization depends heavily on the exact temperature and the time you hold there, and most calculators simply weren't built for it. Treat any predicted IBU from a sub-boiling stand as a loose estimate at best, and dial it in by taste over a couple of batches. Second, and this surprised a lot of us: the IBU number you measure no longer means quite what we thought. In a heavily late- and dry-hopped beer, oxidized alpha acids called humulinones get pulled into solution without ever seeing a boil. They register on the standard IBU test almost like iso-alpha acids, but they taste only about two-thirds as bitter. The upshot is that a modern hop bomb can lab out at a frightening IBU while drinking far smoother than the number suggests. Don't chase a target IBU on these beers. Brew to flavor.

What we've learned since

Everything above still works, and it's where I'd tell anyone to start. But the picture is bigger now. Four developments in particular have changed how the best hoppy beers get made, and none of them were on my radar when I wrote the first version of this. If you only adopt one new thing, make it the first one.

The temperature-controlled whirlpool

Back then we talked about adding hops "in the whirlpool" as if the kettle were still near a boil. The single biggest upgrade since is learning to cool the wort before the whirlpool hops go in. Isomerization (the reaction that turns alpha acids into bitterness) essentially shuts off below about 175°F (79°C). So if you knock out, let the wort drop to somewhere in the 170–185°F (77–85°C) range, and only then add a big charge of hops and hold them there for 20 to 40 minutes, you extract a tremendous amount of oil with very little added bitterness or harshness. This is how modern breweries get those layered, juicy aromas that survive into the glass. Push the stand temperature higher and you'll pick up more bittering and a bit more of that cooked, marmalade hop note; drop it toward 160°F (71°C) and you keep things more delicate and fresh. I like to target the low 170s°F (around 77°C) as a starting point and adjust from there. The one rule that hasn't changed: when the stand is done, chill and get off the hops as fast as you can.

Biotransformation: let the yeast do hop work

For years we treated dry hopping as a purely physical soak: hops in, aroma out. We now know the yeast is an active partner. If you add dry hops while fermentation is still going, roughly the first one to three days while there's a healthy krausen, yeast enzymes go to work on the hop compounds. They free aroma molecules that were chemically locked up and unsmellable in the raw hop, and they convert some compounds into others: geraniol, for instance, gets nudged toward citronellol and linalool. The result is often a brighter, fruitier, more "alive" aroma than the same hops added to finished beer. I'll be honest about the limits: the effect varies by strain and variety, vigorous fermentation can scrub off some of what you're trying to keep, and not everyone agrees it always beats a cold, post-fermentation dry hop. But it costs you nothing to try, and on the right beer the difference is real. Dry hop a portion at high krausen, save the rest for after fermentation, and taste the two approaches against each other. That's how you'll learn what your yeast and your hops want to do together.

Thiols and the tropical frontier

If you've had a recent beer that practically explodes with passionfruit, guava, or white grape, you've met polyfunctional thiols. These are sulfur compounds (3-mercaptohexanol and its relatives) that the nose detects at almost absurdly low concentrations, parts per trillion. Here's the fascinating part: they're mostly not in the hop as aroma at all. They ride in as odorless, bound precursors in both the hops and the malt, and it's the yeast that snips them loose during fermentation. That has opened a whole new lever. Some hop varieties (Talus, Sabro, and certain lots of Citra and Mosaic) are unusually rich in these precursors. There are now thiol-releasing or "thiolized" yeast strains bred or selected specifically to free more of them. And there are precursor products such as Phantasm, a powder made from Sauvignon Blanc grape skins, that you add to boost the raw material the yeast has to work with. This is the genuine cutting edge, and it's where a lot of the most striking new hop character is coming from. You don't need any of it to make a wonderful hoppy beer the old way, but if you want to chase that intense tropical note, this is the door.

Dry hop creep: the catch we didn't know about

One thing the old article couldn't warn you about, because we didn't understand it yet, is dry hop creep. Hops carry their own enzymes, and when you dry hop, those enzymes can break residual dextrins (sugars yeast normally leaves behind) into fermentable sugar. If there's any yeast still around, and there usually is, you get a small second fermentation. That sounds harmless until you realize what it means in a sealed package: the beer keeps attenuating, gravity drops further than you planned, carbonation climbs, and you can end up with gushers or even dangerously over-pressurized bottles. Worse, that renewed fermentation can throw diacetyl, the buttery off-flavor, with nothing left to clean it up if you've already packaged. Tom Shellhammer's lab at Oregon State did much of the work that put a name to this. The practical defenses are simple: dry hop while you still have healthy, active yeast and the beer is warm, give it a few extra days of warm conditioning after the dry hop so the yeast can finish the new fermentation and mop up any diacetyl, and never bottle or keg a freshly dry-hopped beer that's still showing activity. Concentrated lupulin products carry less of this enzyme load, which is one more quiet point in their favor.

Other tips for late hopping

• The time from adding the hops until the wort reaches pitching temperature affects both character and bitterness. Brynildson: "If you throw hops into the whirlpool and then take two hours to cool, you will not get the effect you are looking for." Add late hops at the last possible moment, then cool and transfer as quickly as possible.
• Protect your aromatics from oxygen. This is a newer emphasis and a critical one. The bright hop aromas you worked so hard for are fragile, and oxygen picked up after fermentation will dull and "cardboard" them within weeks. Minimize splashing on transfer, purge your kegs and bottles, and drink your hoppy beers fresh and cold. No amount of late hopping survives a careless cold side.
• Sousa suggests increasing wort volume: you'll lose some wort to the large hop mass, so add an extra quart per five gallons.
• High wort pH emphasizes harsh bittering, so hold off on "Burtonizing" your water with mineral additions.
• Zien's summary: explore your own boundaries; don't be limited by the hop amounts on most recipes. Use the malt bill to create a profile that showcases the hop character you want, and always use the freshest ingredients: taste and smell your grains and hops.