Fine-Tuning Bitterness, Reusing Yeast, Dry Hops in a Carboy, and a Racking Question

Q I’ve often wondered if there is an easy way to adjust bitterness post fermentation. I’ve read about a few techniques (Isomerized hop extracts, boiling hops in a small volume of water/starter wort, adjusting water profile, blending, etc.) and I’ve also read all the reasons why some of these may not work.

I’m mostly interested in adding something to the keg (Hop extracts or boiling a small volume of water/wort and adding it). If my beer did not hit the bitterness, I’m most likely just going to roll with it rather than brew another batch and go through the trouble of blending. I also use a sulfate-heavy water profile for my hoppy beers already so adding more probably won’t get me what I am looking for. I’d love to hear your thoughts on the best ways to go about this.

Mike Figuray
Woodbridge, Illinois

A At times it is helpful to review why some brewing problems are not so easy to fix and discuss how to prevent these problems in the future. Under-hopped beers are an example of a problem that is not so easy to correct after a certain point in the process. You have noted several possible fixes, including the two primary ways to go about adding bitterness post fermentation, so let’s start with these possible solutions and then my suggestions.

Adding a pre-isomerized hop extract is really “the way” to boost beer bitterness after fermentation. While this process is pretty simple, there are a couple of drawbacks. The first is that measuring these extracts is not the easiest thing to do because the addition rate is rather low. For example, it only takes 200 mg of iso-alpha-acids (IAA) to boost the bitterness of 20 L (5.3 gallons) of beer by 10 IBU. Even if the extract is dilute and contains 33% iso-alpha-acids (IAA) by weight, only 600 mg of extract is needed for this addition. Attempting to weigh out this volume of extract is not practical, so the most common method of measuring these additions is by volume. But that is also a challenge because extracts tend to be thick and sticky. Using more dilute solutions makes this process more manageable; this is also true of benchtop trials to determine the addition rate as well as making the addition to your batch.

Another thing about post-fermentation adjustments to bitterness is that you will not be adding much hoppiness to your beer. If you have never adjusted bitterness with an IAA extract you may be surprised by the one-dimensional nature of the change. You will not get any hop aroma or mouthfeel characters from hop polyphenols that often accompany kettle additions. Adding IAA extract simply adds pure and clean bitterness. If that’s what you are after, then this method will certainly work for you.
Your other suggestion about making a hop extract is certainly another option. Although hop acids are partially soluble in aqueous solutions, the solubility of IAA increases as pH decreases (Rudin, A.D. Solubility of Iso-Compounds in Water and Their State in Solution. Journal of the Institute of Brewing, 66 (1960): 18-22.), where the solubility is approximately 600 mg/L versus 900 mg/L in wort. In neither case is the solubility high enough to produce a highly concentrated extract. Increasing the bitterness level of 20 L (5.3 gal.) of beer by 10 IBU (10 mg of iso-alpha-acids per liter) requires 200 mg of IAA; assuming the stock concentration is 900 mg/L, this boost of 10 IBU requires 227 mL of solution. As the desired boost in bitterness increases, so does the volume of dilute hop extract. And if wort is being added to fermented beer, fermentation is required. If the fermented beer to which this solution is added is not cold and has a decent cell count of healthy yeast in suspension, this sort of addition should ferment out without any major problem.

There are quite a few new products in the market for brewers, including less viscous hop extracts, that can be used in multiple ways, from adding bitterness, to boosting flavor and aroma. Photo by Jake Parrish/Yakima Valley Hops

Blending is definitely a viable option if you happen to have some overly bitter beer hanging about that would benefit from mixing with a batch that is low in bitterness. While blending is common in commercial brewing, it is usually used to improve the consistency of already consistent batches. The type of blending where two extremes are blended to yield something in balance is more of a Hail Mary play and the result is not something that is easily brewed again. Similarly, deriving significant bitterness from water salts falls outside of normal practices.

To be honest, if this were my beer I would either add some IAA extract if the bitterness is really low or simply roll with what you have and call it good. Making an extract from water or wort introduces a step that could end up making a marginal situation worse. It’s like making a batch of chili that is too spicy, fixing the problem by diluting, and ending up with a really big batch of mediocre chili! But this is a great opportunity to learn from the problem.

Adding a pre-isomerized hop extract is really “the way” to boost beer bitterness after fermentation.

Beer bitterness is one of those things that has bugged me for a long time because too many brewers and beer consumers talk about IBUs like the numbers really mean something definitive. “Man, I had a beer yesterday that was 60 IBUs and it was like totally not bitter! I don’t know what beer calculator the brewer was using, but the beer was NOT 60 IBUs.” Many of us have probably heard or read this sort of thing. I usually do an eye roll and turn my back to this sort of nonsense because it’s simply not a debate I enjoy having. The problem with these blanket statements is that the sensation of bitterness is not just about the concentration of iso-alpha-acids in beer. Hop bitterness is akin to a spice and is balanced by malt flavors (toast, caramel, chocolate, coffee, etc.), residual extract (sweetness), alcohol, carbonation, and other beer components that factor into complexity. More hop bitterness is generally required to provide balance as the bigness of a beer increases. This is why I have a thing against brewers using IBU levels as an indicator of sensory bitterness. 60 IBUs in a luscious, high-gravity stout is not likely to be perceived as overtly bitter. Put the same hop additions in a Pilsner and the story changes. OK, off of the hop bale.
There are several take-home messages from your current problem. Here are four to consider in the future:

  1. Aiming for a bitterness target requires knowing the alpha-acid content of your hops. If a recipe calls for 20 grams (0.7 oz.) of 10% alpha Magnum hops, and you have 8.5% alpha Magnums, more hops are required to obtain the same bitterness.
  2. Hop acids degrade with aging. This is a complex topic unto itself because oxidized alpha acids are bitter, but they are not as bitter as IAAs. Hop age, oxygen exposure, and storage temperature all factor into the brewing value of hops. Just because a bag of Magnum hops contained 10% alpha when they were harvested does not mean that the hops in the bag haven’t changed since packaging. Be mindful of the age of your hops and how they were stored.
  3. Be consistent with hop calculations and calibrate your brewery’s bitterness scale with itself. It’s more important for you to know that a 30-IBU pale ale brewed on your system has a certain level of bitterness than it does to actually know how your beer compares to someone else’s 30-IBU pale ale. Since few homebrewers ever have their beers analyzed for bitterness, it’s more important to be able to adjust your perceived bitterness using calculations that you use as a guide. The biggest unknown when calculating bitterness is hop utilization. Using the same reference guide and adjusting for gravity is a great way to be internally consistent with your methods.
  4. If you are just starting to formulate your own recipes, keep in mind that the IBU target changes with the type of beer you are brewing. Big, malty beers, like doppelbocks, are often much higher in IBUs than they taste.

Q I have been having an issue with my fermentations when reusing yeast after rinsing. I am not sure if it is sanitation since it only has happened when using 3rd–4th generation rinsed yeast. The yeast in these cases dries out the beer (FG = 1.006 instead of my usual 1.014–1.016) and the beer is not as hazy as is typical (NEIPA). the beer is yeasty with some notes of oxidation. It was a standard infusion Mash at 67 °C (153 °F) and fermentation temperature was 18–20 °C (65–68 °F). Oxygenation rate was 2.5–3 L (2.6–3.2 qts.) per minute for 1 minute and I do it directly with a ½-in. hose (I know that’s risky but I always perform it the same way). I read an article at about wort over-oxygenation when using harvested yeast. What could I do to avoid these issues?

Roberto Caballero
Lima, Perú

A Troubleshooting issues with harvested and washed yeast is difficult without having more information, but you have provided lots of good discussion points. In your case, you are taking yeast from NEIPA fermentations, rinsing/washing your yeast presumably with water, and re-pitching. And your major problems are increased attenuation and less haze, but you are also thinking you may have some oxidized beer flavors.

Let’s start with the increased attenuation levels. Assuming you are brewing similar beers over time, which seems to be your case, the most common cause of this issue is either wild yeast or enzyme contamination. So-called diastatic yeast strains secrete the enzyme amyloglucosidase (AMG), also known as glucoamylase, resulting in the digestion of dextrins in beer into glucose, followed by the fermentation of this glucose by yeast. When diastatic yeasts are present in your pitching yeast, the result is abnormally dry beer. The same sort of thing can occur if yeast is harvested from fermentations where AMG has been added from exogenous sources (i.e., from a bottle). Although dry, light, and brut styles are the beers that come to mind when thinking about AMG additions, high dry-hopping rates are also associated with the problem that has become known as hop creep. If yeast is cropped from dry-hopped beers, AMG enzymes from hops can be carried with the pitching yeast and potentially lead to issues in subsequent batches.

I am speculating about the cause of your increased attenuation with yeast generation, but it is certainly not uncommon for one of the above problems to occur. In the case of diastatic yeast strains, phenolic off-flavors are almost always present. It is more common to see the terms “diastatic” and “POF+” (phenolic-off flavor positive) on yeast data sheets these days because brewers have become increasingly aware of special handling required for these strains. To be clear, many great brewing strains, such as all saison strains, are diastatic and POF+, so there is nothing inherently bad about these strains. As it turns out, many wild yeasts, such as Brettanomyces, are also diastatic and POF+. Depending on how you are handling your yeast and what background microflora you have in your brewery, you may be experiencing low-level contamination from wild yeast. If forced to choose a cause of the increased attenuation, wild yeast would be my pick.

In the case of diastatic yeast strains, phenolic off-flavors are almost always present.

Your next issue is the loss of haze over time. As an old-school brewer, it is really weird to be discussing improvements in clarity with subsequent generations as a problem. Back when I was a kid, we learned that brewing yeast, particularly lager strains, can lose their flocculation properties over time. And setting a generation limit is a common way to prevent the loss of flocculation over time. It also seems, in the case of hazies, that reusing yeast can also lead to overly clear beer!

Not sure what is up with your question about oxidation, but have heard that many brewers who recycle yeast from NEIPA brews are experiencing problems related to yeast health. And beer freshness is something that suffers when unhealthy yeast (i.e., low viability and low vitality) is cropped and re-pitched. Although the problems encountered by many a NEIPA brewer cropping yeast from dry-hopped beers is not related to wort oxygenation, high wort oxygen levels can result in oxidative damage to pitching yeast, and this cellular damage takes multiple yeast generations to manifest itself with poor yeast performance. Don’t know if that is what you are experiencing, but that is the main argument against high oxygen levels achieved using pure oxygen to oxygenate wort, as opposed to using air for aeration with a lower oxygen solubility.

OK, let’s pull some take-home messages from this meandering discussion:

  1. Based on the general description of your observations, I suggest limiting the number of times you re-pitch yeast. Generation count may not be the direct cause of your issues, but there is something that seems to be changing over time. Removing reuse will help you narrow down the root cause of your problems.
  2. Consider reducing your oxygenation rate and using a smaller hose so that you get smaller bubbles (better gas diffusion). I am assuming you are doing 20-L (5.3-gal.) batches, so you can adjust my math if this assumption is wrong, but 2.5 L (2.6 qts.) of oxygen contains about 3.6 grams (22.4 L per mole and the molecular weight of oxygen is 32) of oxygen. If only 10% of this gas dissolves in the wort, that is about 18 mg/L of oxygen, which is a bit on the high side. Most textbook references cite 8 mg/L as the norm (probably because that coincides with the oxygen solubility in cool, 1.048 standard gravity/12 °Plato wort from air).
  3. Review your sanitation practices since you questioned that as a possible issue. Bleach is a great “bomb” if you want to just give your whole kit a severe hit (avoid on stainless steel). Thoroughly rinse, drain, dry, then clean and sanitize as normal before your next brew. Low-levels of Brettanomyces can be challenging to kill and bleach is a good way to deal with hard-to-kill microbes.

Q I have a specific question about single fermentation dry hopping in narrow-mouth glass carboys. I like to dry hop my NEIPA in two stages: One around three days into fermentation and the second addition around day 8. If I don’t want to leave my first batch of three or so ounces (~85 g) of dry hops in my carboy, how can I get them out? Using hop bags is difficult with the narrow mouth of glass carboys. Or is it OK to simply leave the hops in for 10–12 days?

Menno van Burken
Manchester, Vermont

A There are some problems best solved by changing tools. The easiest way to add and remove hop bags to a carboy is to use the types with large openings. Just guessing that’s not the reply you were seeking! Another approach is to put your hop pellets in an over-sized hop bag to allow plenty of room for expansion and movement within the bag; before putting the bag in your narrow-mouth carboy, tie a piece of fishing line to the bag so you can pull the bag out of the beer (and maybe out of the carboy) at the right time. If the bag is too large to easily pull from the carboy, simply tie your line to the neck of the carboy and let the hop bag hang above the beer level until you have racked your beer when it’s easier to wrangle the bag out.

I understand the desire for simplicity, but there are times when investing in new equipment, like a carboy with a wide mouth, or adding another step, like racking from one carboy to another carboy (or keg), is likely to improve your beer. Leaving dry hop additions in contact with beer for prolonged time periods is one of those practices that often results in less-than-stellar beer with grassy/green-tea/vegetative and astringent hop flavors. Method aside, avoiding these flavors in NEIPAs is generally a good thing.

Q I am brewing a saison and after 12 days the fermentation is nearly over, but there is still activity. The thing is that I need to use my fermenter this coming weekend for a new batch and I’m wondering if I can transfer my saison from my Unitank to a FermZilla All Rounder (a PET fermenter) to Finish. Do I transfer all the yeast and beer (via dump valve) or only the beer (via racking valve), as if I were transferring to a keg after crash cooling?

Nici van Nieuwkasteele
Lommedalen, Norway

A Racking beer from your stainless conical to a PET secondary fermenter is a great way to free up your stainless fermenter. If you have yeast in the cone or trub, I would suggest either clearing the bottom and moving all of the beer to your All Rounder, or transferring out of the racking valve if you don’t have to sacrifice much beer for this transfer. Getting beer off of yeast after primary is complete has flavor benefits because prolonged contact between beer and yeast can result in autolysis and accompanying soy sauce/yeast/umami flavors. The bottom valve on your conical fermenter can normally be used for this purpose, and is a very handy tool. There are no major issues with your general plan to free up your fermenter and you should have plenty of yeast in suspension to finish the fermentation.

Issue: January-February 2021