By Greig McGill
There’s been a lot of buzz over the last few years about the supposedly newly discovered phenomenon of hop creep. In fact, hop creep has been a known factor since 1893! But now that we’re using more and more dry hops in our insane IPAs, it’s becoming much more of a problem we need to be aware of and know how to mitigate.
So what is hop creep? Simply put, it’s an extra stage of fermentation caused by enzymes in hops breaking down previously unfermentable longer chain sugars into shorter chain sugars that residual yeast can ferment. The effects of this are drier beer, higher abv, more carbonation (produced anyway, perhaps not retained depending on packaging time), and other fermentation by products such as VDKs like diacetyl.Take a deep breath now, because here comes the longer explanation by way of SCIENCE!
An enzyme is either a protein or RNA, and acts as a catalyst to speed up a chemical reaction. Enzymes, despite those cool washing powder ads in the 80s and 90s, are not hungry, nor even alive. That said, like people, they function only under certain conditions and in certain environments, and can be denatured - de-activated - outside those conditions. The enzymes we’re worried about are diastatic (starch converting) and/or amylolytic (starch-degrading). The former are commonly associated with many bacteria, and also with diastatic strains of yeast. The latter are found in hops. When these enzymes are high enough in number, and come into contact with otherwise unfermentable carbohydrates in the form of long-chain dextrins in your pretty-much-fermented beer, they will break them down into fermentable sugars, and the remaining yeast will attempt to ferment them.
OK, so why is that a problem, it’s just a bit more fermentation, right? Well, that yeast that’s left at this stage simply isn’t equipped to perform a healthy fermentation. Sure, it’ll chew up those sugars and spit out CO2 and ethanol, but it’s tired and beaten up from all that budding and prior fermentation. Its cell walls are thin and scarred. It’s depleted almost all the resources it needs to ferment cleanly and it’s also in a hostile environment, already way higher in CO2 and ethanol (waste products), and way lower in oxygen than it needs to be in order to properly clean up after itself. So sure, you’ll get a bit more alcohol, but you’ll also get lots of bad stuff, primarily VDKs like diacetyl. The end result: your beer will be drier, higher in alcohol, and probably a little (or a lot) buttery. Not ideal!
The subtle and annoying part of hop creep is that it might happen very slowly, giving you a beer at packaging time that tastes great but a few weeks later is a butter bomb. So long as there is live yeast involved, the rate of hop creep is hard to predict or account for.
Why has this only recently become “a thing” then, if we’ve known about it since 1893? I’m sure you can guess, and as I mentioned in the introduction: the hops arms race! Yep, your favourite hazy IPA generally has a huge dry hop load - orders of magnitude more than were ever used in dry hopping in the past. That means a much higher enzymatic load, and much stronger effect from that extra fermentation. Other factors have also contributed, like the rise in popularity of higher enzyme-bearing hops over the last 40 years or so, as well as the proliferation of diastatic positive yeast strains
So what can be done to prevent hop creep? Unfortunately, the short answer is “nothing”, unless you have the ability to completely remove yeast from your beer before dry hopping, or you don’t mind the risky pre-heating of your hops before use, which will reduce their aromatic potential but will denature the enzymes. There are many things you can do to mitigate it though. I’ll start with the least helpful one first… lower your dry hop loads! Yep, OK, that’s a non-starter. But seriously, there’s now research out there that suggests that we’re just not getting much actual benefit from dry hopping at a level above 8 grams per litre. Our friends at Brülosophy tested this and their conclusion supported the research. Many in the industry simply don’t believe the research though, and will continue to push the boundaries of just how much hop matter they can cram into their fermenters. If nothing else, it sounds great on the marketing blurb!
Another option is to fight enzymes with enzymes. Assuming you don’t mind the extra ethanol, and just want to prevent diacetyl formation, you can use ALDC (alpha acetolactate decarboxylase) at the beginning of fermentation in a beer you intend to dry hop. This will inhibit diacetyl production by converting the precursor, acetolactate into a flavourless compound called acetoin.
If you don’t mind doing what the wine industry has been doing for years, you can prevent further yeast activity, and thus limit hop creep, by adding sulfites to your beer before dry hopping. Sulfite (usually in the form of sulfur dioxide - and yes, I am going to spell it like an American) has an inhibiting effect on yeast. Just be aware that while the science currently says that sulfites don’t cause headaches or harm people, they are a known allergen, so it is worth advising people who will drink your beer if you go this route.
If you find that hop creep isn’t too much of a problem, and simply want to do your best to reduce it, you can play around with the various variables. Lower hop loads, less contact time on the dry hop, minimal residual yeast levels, and cooler temperatures will all help to reduce hop creep.
Of course, even if you fear the dreaded creep may still occur, you can slow it right down to the point that hopefully your beer is gone before you notice it. Just ensure the beer remains as cold as possible at all times. You can always let it warm up in your glass if you prefer a slightly more flavourful experience at a warmer temperature. Or do what I always do… pour two - the first for the thirst, the second to savour!