Yeast Viability Over Time

When you buy a pack of liquid yeast, there are two things you should be aware of. One is how many cells are in the pack. For yeasts by WYeast and White Labs, that number is typically about 100 billion cells. For other manufacturers like Omega Yeast Labs, that number is roughly 150 billion. The second thing you should be aware of is the packaging date. The packaging date is important, because conventional knowledge tells us that yeast viability decreases by about 20%-25% a month. So, to calculate proper pitching rates or yeast-starter size, the date is needed to get an approximation of how much viable yeast is available.

Earlier this year, Brulosopher, of BRÜLOSOPHY, posted a short article on his yeast-harvesting method. Basically, the idea is to make a starter larger than you need and end up with roughly 80-100 billion cells in excess so that you can build a new starter from the yeast in the future. This method is cleaner and less time consuming than previous methods, which include washing the yeast from a previous batch and re-using that.

I started harvesting yeast using Brulosopher’s method a couple month ago, not for every batch but absolutely for those that use yeast I plan on using again, like Scottish Ale Yeast from WYeast or The Yeast Bay’s Vermont Ale Yeast. The problem is that yeast is only viable for so long, which is why the packaging date mentioned earlier is important. Now, everything pertaining to yeast cell counts is a gamble. 100 Billion cells is almost never actually 100 Billion cells, but can fit within a range. So, moving forward, we need to operate under the assumption that these numbers are general answers, and not specific case instances. We are also going to assume storage at refrigerator temperatures in liquid cultures.

Why Can’t I Store Yeast Forever?

Yeast is a living organism, and so it can’t just sit forever. As yeast sits, it slowly begins to consume its glucose reserves, weakening its internal structure and eventually resulting in the yeast’s cell walls rupturing, killing the yeast. This rupture is actually what is responsible for autolysis, a factor of off-flavors in beer.

So, if you can’t store yeast forever, how long can you store it?

Yeast Viability Over Time

As far as yeast viability over time goes, there are a few different answers as to the “shelf-life” of yeast. BeerSmith, popular brewing program, uses something like:

1 Month: 75%
2 Months: 59%
3 Months: 46.5%
4 Months: 35.5%

To elaborate, there is a non-linear 20% decrease in viability per month. That means that if you begin with 100 billion cells, then after a month you would have 80 billion cells. After two months, you would have 64 billion cells. So the 20% decrease is not from the initial cell count, but from the cell count at the beginning of the measuring period. This non-linear model is the same model that the blog Homebrew Dad uses in its yeast calculator.

So, obvious flaw, this model would result in always having some semblance of live cells, which isn’t the case. Eventually, all the yeast will be dead (things are getting dark here…). However, I’m not sold on the 20% decrease in viability. This is mainly for anecdotal reasons, but that’s enough for me to start looking.

What’s the Max Amount of Time I Can Store Liquid Yeast?.

Before doing my own research, I turned to people who certainly have more experience than me.

The first  point comes from Brian of Brouwerij-Chugach in his response to /u/UberG33k of Immaculate Brewery. /u/Uberg33k asked if anyone maintained a yeast bank, a collection of yeast to be cultured and used for future batches. Here is Brian’s response.

Basically, he gives some speculative timelines for storing yeast. His assumption for liquid yeast at refrigerator temperatures is one to two years (you absolutely need to use a step-starter to build it up at this point). I think this is a little optimistic, but Brian knows what he is talking about, and my doubt in the 20% numbers gives me enough of a reason to believe there is something to this.

Second point comes from some emails I received from The Yeast Bay and White Labs.

The Yeast BayIf you’re unfamiliar with The Yeast Bay, go ahead and check it out. There is some awesome work being done in making some less-available strains more accessible. Personally, I’ve only used Vermont Ale Yeast, supposedly cultured from the famous Conan yeast. I also plan on using either their Saison Blend or Wallonian Farmhouse Yeast in a Belgian Dark Strong/Imperial Dark Saison I’m planning. In my response, Nick (founder of The Yeast Bay) mentioned that there are a lot of factors that go into yeast viability over time, and that there isn’t a one-size-fits-all answer. Nick says to use a yeast calculator to determine viability, because these approximations are all we have.

White Labs also mentioned there were too many factors to accurately determine yeast viability, however they did mention something that was in line with what Brian said from earlier, that, even under poor conditions and a long period of time, a few cells can remain viable (in theory) to culture more yeast from.

So, what defined “poor conditions” from a time standpoint? Michael Nicholson and Brooke Pearson from Oxnard college seem to think two years. In their piece, Nicholson and Pearson explore yeast viability with old and new strains of dry yeast and liquid yeast. For our purposes, the most interesting parts of their findings are that:

A: If both are fresh, liquid yeast outperforms dry yeast until about 130˚F. Important, because this demonstrates liquid yeast’s vulnerability to temperature, which makes storage temperatures even more important.

B: Old (two years) liquid yeast failed to ferment at all.

So, glad we found a roof on this thing. But two years? That’s the high end of Brian’s estimate, and way beyond the 6 months that a 20% linear depreciation rate would give. So what do the actual numbers look like?

Yeast Viability Depreciation

Obviously, the answers above aren’t specific enough enough. They point to a longer storage period than 6 month, but not to the actual viability of yeast. But it gives me hope. Take a look at this experiment detailed on Beer Advocate. All credit to LeeryLeprechaun.

In this study, LeeryLeprechaun split a starter of WYeast 1056 and tested its viability using a hemocytometer and methylene blue. He got the following results:

Culture Age: 3 Days
Viability: 98%

Culture Age: 10 Days
Viability: 97.75%

Culture Age: 19 Days
Viability: 96.6%

Culture Age: 31 Days
Viability: 81%

Culture Age: 38 Days
Viability: 80%

LeeryLeprechaun decided to restart his tests after this and I haven’t seen any other results. However, his findings are consistent with the 20% depreciation rate, but absolutely blows WYeasts recommended storage time (max two weeks) and the “50% viable after two weeks” number out of the water.

This next article is from Woodland Brew. If you’re interested in the specific details of the article, please give it a read. It is an awesome article.

The 20% decrease equates to roughly a .7% decrease in viability a day. Steven, the author of Woodland Brew, tested seven different yeasts and found an average of .2% decrease in viability a day. This changes the 20% a month depreciation rate to about 6%. This is awesome information, particularly because Steven is clear that his samples are refrigerated and that is what we are interested in. Steven has also posted this on Reddit before, and honestly deserves some more credit for the post.

So, here we have a much smaller depreciation rate, which is fantastic. But should calculator’s change their conditions because of it? Personally, probably not. A 20% depreciation rate means there are less cells available, and so a larger starter (or more step starters) would be recommended, which won’t hurt anything and could result in more cells overall. This could possibly lead to over-pitching, but over-pitching can be a bit difficult to achieve on a homebrew scale.


The point of the findings here is that you can absolutely store yeast for longer than six months, and that 20% depreciation rate is bunk if you are storing yeast under good (not even optimal) conditions. The 20% that Jamil claims is a good rule of thumb, but I think there is sufficient evidence to claim that it isn’t a dead-on number. Maybe not even all that close.

Without a microscope, there isn’t much more I can do in terms of this, but I think there is enough here to warrant more tests. I am going to continue sending emails, hopefully someone with a background in yeast and chemistry finds it interesting and would be willing to conduct the tests. If so, I’ll keep you all updated.

Moral of the story? Your yeast is probably more viable than you think it is, so get that starter going!

So How Do I Store Yeast for a Long Time?

If you want to save some liquid yeast but don’t know when you’ll be able to use it, or if you want to start a small yeast bank, here is what you should do to store your yeast:

  1. Make sure you are storing your yeast in cold temperatures, the ideal temperature range is about 33˚F-38˚F¹. Never let the yeast freeze, try to keep it as cold as possible. I’d aim for 34˚F.
  2. Store it with the same wort you would use for your yeast starter, low OG (1.040)  and no hops.
  3. Store it in a sterile container.
  4. Store it with as little oxygen as possible.
  5. In storage, yeast can still produce Co2 for a while since most refrigerators aren’t cold enough to stop the yeast immediately (and you wouldn’t want ti to be that cold in this case). For this reason, you want to release Co2 from the container every now and then for the first day or so.
  6. Store in sterile plastic, in case the Co2 builds up. Plastic should be more resistant to the pressure. I personally use these test tubes.

Always make a starter, and if you are storing longer than six months I would recommend using a step-starter. Use a yeast calculator. Even though the 20% number is more than likely not accurate, it is a popular rule of thumb and can give you a general idea of how large a starter you should be using. Plus, if you have more viable cells than the calculator thinks, than that’s a bonus.

If you want to store yeast for longer than a year, or want to have a larger bank, you should look into storing yeast on a slant and freezing it.

Hope this was helpful for all of you, it definitely was for me!




Czech Pilsner Planning Post

I have a friend named Evan who is currently teaching English in the Czech Republic. I don’t have too many opportunities to talk to him, but in one of our first conversations he was sure to mention one of his favorite parts of his travels: the beer.

Specifically he enjoys the pilsners. He detailed how light they were, but somehow full of flavor. He likes them because they’re sessionable, delicious, and light. Nothing, according to him, like the beers here in America.

Perhaps I shouldn’t have taken this conversation as a challenge, but I couldn’t see it any other way. I needed to make a Czech Pilsner.

Pilsner Urquell, Plzensky Prazdroj

Some Analysis

For a wonderful, brief write up on Bohemian Pilsners, check out this /r/homebrewing post by /u/NickoSuave311

The Czech Pilsner, or Bohemian Pilsner, is a beer that was born in the western half of Czechoslovakia. The world’s first pilsner, the Pilsner Urquell, is still brewed there today. The pilsner style rapidly spread, and with the advent of modern refrigeration lager brewing became more accessible.

So what makes this beer so excellent? Why is it so different than the light lagers we are used to? Where does all that flavor come from?

Well, for one thing, the water. Water used in the brewing of the Czech Pilsner is incredibly soft, about 50 ppm of dissolved liquids. This water is incredibly distinctive, and brewers attribute the water as the cause of the soft hop flavor that comes through in the Pilsner Urquell.

The grain bill certainly can’t be overlooked here, because it also leads to the incredibly important decoction.  Czech Pilsners use 100% Pilsner malt. Traditionally, this malt is grown locally in the Czech Republic and surrounding area and malted for the beer specifically. This grain is under-modified, because the Pilsner Urquell utilizes a triple-decoction mash. Modern, well modified malt can suffer from a triple decoction. It can result in poor head retention and affect body. However, many brewers swear by the triple decoction, and the necessity for these under-modified malts. Certainly, many breweries still use this method.

Saaz hops are a trademark of the style, and are also typically locally grown. I’m going to stand by Saaz as the nly hop you should be using for this specific style, partially because I like the tradition but mostly because I believe in simplicity, and all Saaz is perfect for that.

Czech Lager yeasts are perfect for this, and there are a lot of options out there. Myself, /u/NickoSuave311, and /u/BrewCrewKevin are planning on brewing Bohemian Pilsners with different yeasts to see how the yeast really comes into play. More on that in the future once we are all finished.

So there we have the basics of making a Czech Pilsner. So how am I going to go about this whole process?

Live Oak Pilz, Live Oak Brewing Company

The Planning


The first thing to tackle is water. My water is relatively tough. I am not one to get really into water chemistry (I probably should) but for this style it doesn’t seem like it can be ignored. I received some wonderful advice from fellow brewers to use Reverse Osmosis water for this, since it is incredibly (almost too) soft.

However, a lot of sources say that using just RO or distilled water isn’t a solid plan, since the water doesn’t contain any of the nutrients necessary for the beer. I will be making a four gallon batch, 90 minute boil, which will require roughly 6 gallons of water. According to How to Brew, this is the water profile for a pilsner. I am tempted to either use a 2:1 ratio of RO water to tap water or use all RO water and actually adjust that water to the profile. I’ll be crowd sourcing an answer later on. But the water is important here, be sure to pay attention to it if you intend to brew a pilsner.

Grains and Mash

I settled on using Floor-Malted Bohemian Pilsner malt, and I am very excited about it. This malt is straight from the Czech Republic and intentionally under-modified so that it can be used in a triple decoction.

Now, as for that decoction, I am only going to do a single. I am not sold on the triple, and I would rather do a single decoction with confidence than a triple and be unsure.

I am also adding 3% Carapils and 2% Acid Malt to the mash, in an attempt to get some head retention and lower the pH a bit. I don’t think the pH will be that different, but since I don’t plan on using lactic acid I figured I may as well give it a shot. In future versions, I may control the water chemistry more, but that will be another post.


All Saaz! I’m going to FWH with Saaz and have a big Saaz 0 minute addition. Should be sufficient! Looking to hit 37.7 IBUs.


Like I said, /u/NickoSuave311 and /u/BrewCrewKevin and I are going to be using a lot of different yeasts. I personally am going to be testing out WYeast 2001 Urquell Lager Yeast and 2124 Bohemian Lager yeast. I’m going to ferment at 48F until FG is stable, skip the D-rest, and lager for four-six weeks at 35F.

So there you have it! The planning post. I will hopefully get around to brewing this on Saturday and I will have a full write up of everything then. Until then, if you have suggestions for the style I’d love to hear them!

Happy homebrewing!


Some Resources

Beer Advocate: Czech Pilsner
BJCP: Category 2B

In Pursuit of Czech Pilsner: Take One

You may remember me talking about a friend of mine in the Czech Republic who is ranting and raving about their Pilsners, and that I took said ranting and raving as a challenge. Now, Bohemian Pilsner is not a style that I have a lot of experience with, which includes drinking them. I’m a dark-beer kind of guy, and so a Pilsner on tap isn’t too exciting for me. I gotta say, researching and brewing this beer has given me a new appreciation for this style, it really is a work of art. Simple complexity, difficult to achieve.

Not that I did, but I am pretty happy with the first attempt, and I think I have some solid foundations to move forward with.

In this post, I’m going to be talking about the differences between two types of yeast, and I still need to send these bottles out to some friends who are going to chip in with their feedback and what they think the differences are. So, I will be using the labels 1, 2, and 3 to refer to the beers here, and the ones being sent out were randomly given the letters A, B, and C. The letters were assigned by a friend, so I have no idea which beer is which letter.


After a few more versions and deliberation with some fantastic brewers, I landed on this recipe:

OG: 1.049
FG: 1.013
Boil: 90 Minutes
IBUs: 37.7
ABV: 4.8%

Floor Malted Bohemian Pilsner Malt (95%)
Carapils (3%)
Acid Malt (2%)

Saaz @ First Wort Hop to IBUs
Saaz @ 0 minutes

2 Gallons with WYeast 2124 Bohemian Lager Yeast
2 Gallons with WYeast 2001 Urquell Lager Yeast

While I was working on this recipe, there was quite a bit of debate about the base malt. My original intention behind using it was because of the idea that it was less-modified than standard base malts, and would be better to use in a decoction mash. Turns out, this is a bit debated as to whether or not this is the case, but either way it turned out to be an excellent base malt so I’m going to stick with it. The carapils was for head retention, and honestly this area was a bit lacking, which could be due to my glassware but I also think is a consequence of my inexperienced decoction mashing skills, so the proteins that benefit head retention didn’t make the cut. I’ll probably increase this to 5% in the next batch. Finally, I used 2% acid malt, but really this is negligible and unnecessary. I also don’t have a pH meter, so I have no way of knowing if this helped. In the future, I’m going to get rid of the acid malt, get a pH meter, and probably either use lactic acid or do an acid rest.
The hops turned out really well, but I think next time I’m going to use an even bigger flameout, and maybe even wait until the wort has cooled to 180°F-ish to add more. The aroma was nice, but not as spicy as I wanted it and so that is something to work on in the future. May even dry-hop.

We will get to the yeasts in a bit, but of course I used a starter for the yeasts, considering this needs to be lagered.

Brew Day

I landed on doing a single decoction mash, since I wasn’t totally sold on the idea of decoction, but since a Bohemian Pilsner essentially screams for that sort of mash I decided to go with it. Plus, there are a lot of sources that advocate for a decoration mash, albeit from anecdotal experience. So since I wasn’t sold, and the LHBS owner wasn’t convinced that a decoction beyond the first one would be useful, I went with a single decoction instead of the planned triple.

I ended up following this schedule from HomeBrewTalk. My plan was a protein rest at 126°F for 20 minutes, a sacc. rest at 151°F for 60 minutes, and then mash out at 168°F.

Mash diagram single decoction.gif

Single Decoction Mash. From:


So, heat the water. I always heat about 10°F-20°F hotter than I need to prime the mash tun, then just wait for the water to be strike temp. The water I ended up using, after a lot of deliberation, was a 6:1 ratio of Reverse Osmosis water to Tap water. My tap water is moderately hard, so really I just wanted some of the minerals for the mash. Next time, I’m going to build a more exact profile, but this was about as soft water as I’m going to get without being totally composed of RO water. Rest assured, it was soft water.

Everything was going surprisingly well at this point, but of course, that’s when the problems start. My decoction ended up not being hot enough, and only brought me to 144°F. I didn’t want to heat more water and add it to the mash, and so I improvised by doing another decoction.

The second decoction ended up bringing me to 152°F, which was fine for the time being. Something to take away from this is to really heat your decoction and probably pull a bit more than you think you need to. You can always wait for the decoction to cool down before adding the rest.

So now that the mash is all finished, I added the Saaz to the kettle and started draining the mash-tun.

After the 90 minute boil, I ended up with exactly the volume I wanted, 4 gallons. Let’s call the Urquell Yeast “1”  and the Bohemian Yeast “2”.


For fermentation, I ended up using Brulosopher’s Quick Lager Method. This method has been tried and proven correct many times, and so I had the utmost faith in it. I know I was hoping to go more traditional on this, and I may end up doing a traditional lager schedule in the next attempt, but this time I was convinced that this method would work. My schedule was:

  1. Pitched at 46°F and let it free rise to 48°F, where it fermented for five days.
  2. Removed the probe from the side of the fermenter and let the ambient temp free rise by 3°F, which I repeated every twelve hours until I was at 65°F.
  3. Let it ferment and clean-up at 65°F for 3 days.
  4. Ramped down the temperature to 34°F. This is the only point at which I separated from the quick lager method. I’m of the opinion that the slow ramp down doesn’t matter so much.
  5. Let it sit at this temperature for about two weeks, longer than I had anticipated but I wasn’t too concerned.

The beers ended up having the exact same Final Gravity, 1.012, which is .001 lower than my expected FG. So, I’d say the yeast nailed it.

Now, pretty late in the game, someone asked if I was blending the beers at all. I wish I had thought of this sooner so I could do a blended yeast, rather than just blending the finished product, but I did end up making a gallon of batch “3”, which is a blended batch.

The bottles were conditioned at around 70°F-78°F for about two weeks, and then they sat in the fridge for another two weeks. So a total of a month of conditioning. Next time, I’d like to get a 3-gallon keg and see if I can store it in a friend’s kegerator, because a few reliable brewing friends recommended drinking the beer fresh, so I’d like to try that in the future.

I also went to the store and grabbed some Pilsner Urquell, my friend’s favorite beer from the Czech Republic, and the original pilsner that we discussed in the planning post. You know, for comparison.

The Pilsner Urquell, note the clarity and that golden color. It has a wonderful malty sweetness in the aroma that I’d imagine is tough to replicate, but there aren’t many spicy notes from the hops which disappointed me a little, I had hoped for them to be a bit stronger. Very clean though, nice sweetness. Taste was excellent, a great beer. The carbonation was perfect, very clean, some smooth bitterness from the hops and a wonderful malt-backbone to hold the whole thing up. Honestly not as complex as I had thought it would be, but still a great beer. Not excellent or something to rave about, but great. Honestly, brewing a beer like this would feel like an achievement.

Beer 1, the batch fermented with WYeast 2001 Urquell Lager Yeast. The aroma was a bit spicy, spicier than the Pilsner Urquell, which was fantastic, absolutely what I wanted. I think it could stand to be a bit spicier. There wasn’t much in terms of the malt aroma though. It was certainly present, but lack the complexity that the aroma from the Pilsner Urquell had. The flavor was also lackluster. The malt profile was simple, present, and lacking in complexity. As you can see, the color was nice but medium-cloudy which is far from what I want. The hops were not too present, but they were noticeable. It was a very “eh” beer. If this was the only result of the work, I would start from scratch next time.

Beer 2, fermented with WYeast 2124 Bohemian Lager Yeast, was the superior of the two beers, by far. First off, right off the bat, head retention was better, carbonation was better. This is my error, had to have been a problem with priming sugar, though I swear I was consistent. The color was a nice, straw-color, almost gold, not as brilliant as the Pilsner Urquell but certainly on the right track. It was also fairly clear, and with some work (or gelatin) I feel like it could be crystal clear. Aroma was sweeter than that of Beer One, and it was even a bit more complex, really happy with the aroma. The flavor was clean, complex, and balanced. It was a big step forward. Again, nothing incredible, but I actually feel like I have something to work with here. A good beer, something I’d share with friends for sure.

Finally, we come to Beer 3 which is the blended beer, post-fermentation. It is exactly what you’d think it would be, a step up from Beer 1 and a step down from Beer 2. We will see what others think when I send them out and hear back, but I really wish I had blended the yeast and fermented a third batch, rather than blending post-production.

So, in my book, the clear victor is Bohemian Lager Yeast. When I try this again, I will be doing some more research into decoction, and possibly looking into melanoidin malt as an alternative to decoction. Either way, I’m really happy with how Beer 2 turned out and I can’t wait to really get this style down!

Have a great pilsner? Have tips and tricks? I’d love to hear them!

Cheers everyone!


Developing a Palate for Off-Flavors

When I first started brewing I had no palate whatsoever. I couldn’t taste the difference between any sort of IPA (I still have trouble with this), all stouts were the same, and every beer I made was “good”. As I continued brewing, my palate developed on its own, I never thought about it. I just tried more and more things, but more importantly I started paying attention. Developing that palate (an ongoing process) has been one of the most critical personal improvements in regards to brewing because it means I can identify flavors in my beer that I enjoy and flavors that I dislike. This has really refined my recipe construction process, and it isn’t something I can relay easily through words. This makes it difficult for me to give criticism, because if you don’t have the palate for “astringent” it is difficult for me to accurately describe. As much as I love words, they are often incomplete and under-erasure, useful but flawed (I just brought Derrida into a conversation about homebrewing, you’re welcome).

Why develop a palate for off-flavors?

Because of this trouble in transferring palate through language, it can be difficult to explain to other brewers exactly what is “wrong” with a beer. It is one thing to read How To Brew and think “oh ok, diacetyl is a butter taste” and a whole other to have a perceptive idea of what that taste is.

I find it incredibly important to develop a palate, and especially a palate for off-flavors. If you want to grow as a brewer, this is a great place to start. Now, why especially for off-flavors? Because they are damn tricky.

Off flavors can be sneaky, they aren’t always in your face “oh man this beer is terrible”, they can hide and come out in a way that you just can’t quite place. Developing a palate for good flavors is fantastic, but making sure there are no off-flavors, in my opinion, is the first step.

So how do we develop this palate? I’ve seen a few people recommend intentionally ruining beers, but I just don’t think that works. Too many factors, and there are other perceptive differences that will interfere. The BJCP also sells an off-flavor kit, but that can run $50 as part of a registered course or $100 for a member of the BJCP. Quite pricey. But I do think their approach is better, add a small vial of off-flavor to a light beer and pick up the differences. This is more exact than trying to intentionally ruin a beer via process where a variety of off flavors may be present. But still, a bit expensive and also for BJCP members.

But this is homebrewing, we are largely a DIY group of people, and so in this blog post I am going to talk about replicating these flavors at home so you can learn to identify them. I’m going to start by going through two 5-Common Homebrew Off Flavors articles from the American Homebrewers Association (Article 1 and Article 2) which list some incredibly common off-flavors. There are more and I may explore them in the future, but for now let’s start with the big 10.


Here is a short list of the ingredients you’ll need to replicate all of the off-flavors:

  • Your preferred Macro Light Beer. I personally used Coors Light. Just don’t use Budweiser since there are reports of acetaldehyde in the beer already. Also don’t use Miller, since they use a modified bittering agent that doesn’t react with UV light. We don’t want to throw your perceptions off, though it won’t matter in the long run since you are adding ingredients to it and contrasting the two samples.
  • 1/4 tsp. of White Wine Vinegar (Acetaldehyde)
  • Small sample of cheap bourbon/raw vodka (Solvent)
  • 1/8 tsp. of Tannin Powder (Astringency)
  • 1/2 tsp. of Butter Extract/Imitation Butter (Diacetyl)
  • Small can of corn (DMS)
  • Sunlight (Skunk)
  • Dish soap (Soap)
  • Small copper pipe (Metallic)
  • Incredibly small thing of sherry (optional, based on replicating the two forms of oxidation’s effects) (Oxidation)
  • 1/4 of a campden tablet [sodium metabisulfite] (Sulfur)

I’ll provide pictures of the side-by-side for each of these, the variable will always be on the right and the control will be on the left.


Basically, to prep for each of these off flavors, you are going to want to pour two glasses of your preferred macro light beer, four ounces of each. Preferably use small glasses that you are able to really get the aroma of the liquid from. One of these four-ounce glasses will be your control, the other is what you will add something to in order to replicate off flavors. Clean your glasses in-between tastings, I recommend a quick dip in star-san as well.

If you want to be really thorough, you can also eat some unsalted white crackers, drink a glass of water, and smell coffee beans/lemon slices to reset your palate.

It also may help you to take notes during this process so you can recall the characters you got during these tests. Not everyone perceives things in the exact same way, so a step in developing your palate is understand how you perceive different flavors (even good ones).

Mix the ingredient in and let the beer warm up to room temperature. Smell and taste the glass without the addition (don’t finish it), pay attention to the flavors, mouthfeel, aromas, everything. Now, go ahead and do the same with the beer that has the ingredient mixed in. Again, note everything from aroma, to flavor, to mouthfeel, to appearance. Have some water, and take another sip of the glass without vinegar (you can go ahead and finish it), pay attention to the contrasts.

The Off-Flavors

Acetaldehyde Acetic

Short Disclaimer: Originally, I had this section written as acetaldehyde, and was corrected. These vinegar flavors are actually acetic, rather than acetaldehyde, which can be replicated (supposedly) with green apple jolly ranchers. I will be trying this out soon, and then I will update this, but for the time being acetaldehyde isn’t in this article, and these notes apply to acetic.


How it is Perceived

Acetic flavors are often described as vinegary, in both aroma and mouthfeel.

What Causes it?

Acetic flavors are most often caused by bacteria, typically from an airborne infection during fermentation.

Replicating the Flavor

Run through your prep and  add 1/4 tsp. of white wine vinegar to one of the glasses.

My Impression

At 1/4 a tsp. in 4 oz, the difference is pretty subtle, but it is absolutely there. I get it more in the nose than anywhere else. I wouldn’t categorize it as green apple, but I can see where that imagery comes from. It is more of an acidic tang, it isn’t even something I would categorize as bad unless I had the control right next to me.

For the sake of really exploring the off flavor, I re-poured the glasses and added 1/2 a tsp. this time instead of a fourth. Way more present now, but roughly the same, except now that tang is taking away from the malt profile that I get in the control. It also leaves an unpleasant flavor in the mouth, right on the back of the tongue.

I absolutely recognize this flavor from my own homebrew, and honestly I’m not sure I associated it with acetic flavors before. It really detracts from the beer, and I wouldn’t even call it a terrible flavor, but it does more damage by masking other characters.



How it is Perceived

Astringency is a strong, dry bitterness. Some people perceive it as a mouth-puckering quality. It has also been noted to have some grainy characteristics, which is a nod in the right direction towards where it typically comes from.

What Causes it?

Astringency comes from tannins, and so a common cause for astringency in beer is sparging or mashing far too hot, over 168°F. It can also be caused by the brown-scum byproduct from krausen being mixed back into the beer, over-milled grains, a mash pH exceeding 5.6.

Replicating the Flavor

Take your 1/8 tsp. of tannin powder and dissolve it in a little bit of water. Pour it in one of your glasses, and be prepared for some foam. That dry, puckering quality like sucking on a used-tea bag is astringency.

My Impression


Aside from the obvious color change, the glass with tannins just smells powdery and dry. On the sip, the flavors are a bit muted and the dry-mouth feeling is incredibly obvious. It lingers on the tongue, exactly like the used tea-bag feeling. I get a little of the puckering quality but not much. An easier way to replicate that, in my opinion, is going to the store and getting a cheap, dry red wine. That puckering, dry sensation is what you are looking for.



How it is Perceived

Diacetyl is often described as popcorn-like, with obvious butter characters. It can also contribute a “slick” feeling to mouthfeel.

What Causes it?

Diacetyl is produced by fermentation, and in some styles it is even desirable in limited amounts. More often than not, diacetyl is eliminated towards the end of fermentation. So fermenting too cool and not having a diacetyl rest can be one culprit, it can also be caused by bacterial infections of pulling the beer off the yeast too soon.

Replicating the Flavor

Go through prep and add the 1/2 tsp. of imitation butter to a glass. Stir it in, prepare to be bombarded with butter-characters and a slick mouthfeel. Familiarize yourself with this flavor though, because it is one of the most common off-flavors out there.

My Impression

Gotta admit, I wasn’t looking forward to this one at all. Intense buttery aroma in the nose. The flavor has a popcorn like quality, buttery, still some malt character. I tasted a little of the butter extract, and it is a surprisingly different flavor when it has been sitting in the beer. All the more reason to be familiar with it. I don’t get much of a “slick” feeling, but I imagine I would have had I used more extract or if this was produced naturally. Either way, not a very good character, but an important one to know.

Dimethyl Sulfides (DMS)


How it is Perceived

Commonly referred to as DMS, dimethyl sulfides are often described as vegetable-like, comparing it to creamed corn, cabbage, and green beans.

What Causes it?

During the malting process, S-methyl-methionine (SMM) is produced. Roasting and toasting reduces the amount of DMS, which is why DMS is often most recognizable in light beers that use more base malts. During the boil of the wort, SMM is converted to DMS, and DMS vaporizes and boils off in the wort. So DMS can be caused by short boil times or excessive amounts of DMS. It can also be caused by cooling too slowly, since DMS can be produced post-boil while the wort is still above 158°F. Finally DMS can be caused by a bacterial infection, but when it is produced by bacteria is has more of a rancid sort of character.

Replicating the Flavor

Go through prep and add some of the juice from a can of corn. This is going to be a bit excessive, but if you want you can add more and less juice to a few different glasses to see how you detect it at multiple levels. It might be easier to start high and go low, since you’ll be pushing your perceptive threshold as you go lower.

My Impression

I think this was my least favorite one, because it just made my beer taste like corn. I used 1/2 a teaspoon of the juice from the can, and it absolutely did the job. Not a complimentary flavor to beer, not at all.



How it is Perceived

Have you ever cut yourself and and sucked on the wound? That iron taste from your blood is a metallic taste, often described as tasting like pennies. It is also perceived as an odd metal-like sensation on the palate, which is more of a nod towards mouthfeel than flavor.

What Causes it?

Metallic flavors are often caused by unprotected metals leeching into the wort. This could be from an aluminum or iron cooking utensil/kettle. Stainless steel will not leech metallic flavors. If you’re getting metallic flavors and you use an aluminum kettle, look into proper cleaning procedures for an aluminum kettle and develop a layer of aluminum oxide. It can also be caused by high concentrations of iron in your brewing water.

Keep in mind there are two primary sorts of metallic flavors, iron and copper. They are distinguishable, but both categorized as “metallic”.

Replicating the Flavor

Go to your local hardware supply store and get a small copper pipe. Sanitize it thoroughly. Prep, let it sit for about a minute, then take the pipe out and sample.

My Impression

Initially I didn’t think I got much from this, but mid sip there was a hint of metal and after that sip I noticed ir more each time. Pennies, blood, a metallic twang.



How it is Perceived

Typically, you will hear people describe oxidation as wet cardboard, but I personally perceive a stale sort of characteristic. This can also taste somewhat like sherry.

What Causes it?

Compounds in the beer being oxidized. This could be from excessive barrel aging (where some of the qualities brought on by oxidation are desirable), or from oxygenating the beer while bottling/kegging/in primary/what-have-you. Point is, it comes from the beer’s excessive contact with and exchange of oxygen, post-fermentation.

Replicating the Flavor

This one if a bit tougher, because we can’t directly add oxidation to a beer that will be perceived the same way. One way to replicate the sherry-like qualities is to, obviously, add a little dry sherry to the beer.

As for the stale quality, pour your small glass of beer and let it sit out (out of sunlight) for several hours. Let it sit. You’ll start to notice some stale notes in the beer.

My Impression

So the aroma with the variable glass, which has sherry in it, isn’t terrible. Some sweet fruit-like notes. The flavor though is recognizably like oxidation. It is a bit difficult to describe. It is a little dry, fruit. Not at all unpleasant in small amounts, but I can see how it could quickly dominate. It is also just a flavor that isn’t acceptable in most styles. I don’t get any cardboard here at all.

The “stale” glass, taste bland, blank, and honestly a bit like cardboard, which I found surprising. I didn’t expect to get any of the character, and there is a bit there.



How it is Perceived

Like it sounds, this off-flavor is often perceived as “skunky”, which isn’t helpful for someone who isn’t familiar with the smell, but it is also a bit tough to explain. In my opinion, the smell is comparable to burnt rubber with a sour sort of character. It is pretty terrible.

What Causes it?

Skunking is caused by isohumulone bittering compounds in hops reacting with certain wavelengths in light, notably UV. To be a bit more specific, the “skunky” flavor in beer is 3-methyl-2-butene-1-thiol, or MBT, and is the same thiol that is found in a skunk’s scent gland. Hence, skunky.

Replicating the Flavor

Pretty simple actually. Pour one prep glass, leave it outside in the sun for a few hours (it won’t take this long, but this is about getting reallynoticeable off-flavors in your beer). Pour another glass and let them both come to room temp, and sample. I apologize in advance for you tasting this.

My Impression

I grew up and live in the midwest, and I’m all too familiar with the smell of skunk. A good friend of mine was once sprayed, and the teacher sent him home. I didn’t think a beer could bring me back to that moment in my life, but here we are.

It also reminds me a bit of family re-unions where my dad would let me sip some of his beer, which had unfortunately been sitting with him in the sun for well over an hour. There is a definite skunky quality in the nose and flavor. No burnt rubber at all, but skunk. Absolutely skunk. Blegh.



How it is Perceived

Soap characteristics are pretty much how they sound, soap-y and detergent like, sometimes accompanied by a puckering-quality.

What Causes it?

The typical culprit is, quite literally, soap. This means the use of soap or detergent to clean your brewing equipment/bottles/glasses and the flavor carrying over. Typically, the drinking glass is the problem. It is also possible to get these flavors from leaving the beer on the yeast too long, and fatty acids in the trub can start to break down, creating soap. This takes a while though, so usually it isn’t the issue.

Replicating the Flavor

This one is a no brainer, add a little soap to one of your sample glasses, mix, and try it. Not much to be said, it isn’t pleasant, and it is something you are probably already familiar with, but it doesn’t hurt to learn to pick it out in beer!

My Impression

Pretty much exactly what I thought it would be, a bitter character with a lot of soap. Not the worst one on this list, but still not pleasant. Thankfully the issue is easily solved! Still valuable to know how to call out the flavor.



How it is Perceived

Solvent-like characters are often described as “hot” or as fusel alcohols. Essentially it is a strong alcohol flavor that can be perceived as intense. A solvent-like character is often perceived through the aroma, flavor, and/or mouthfeel of the beer, and are often harsh.

What Causes it?

High fermentation temperatures, low-pitch rates, and a really young beer. Advice a lot of brewers with a solvent problem get is to “let it age” since these alcohol characters tend to mellow out over time. Not that they necessarily will. Solvent characteristics can also be leeched by cheap plastics used in the brewing process and exposed to high temperatures.

Replicating the Flavor

So besides actually brewing a beer and subjecting it to incredibly high fermentation temperatures (maybe make a half gallon?) there aren’t many products I can advocate for to replicate the perception, because it essentially amounts to huffing solvents like cough paint thinner and rubbing alcohol cough. Sarcastic coughing aside, don’t drink this stuff. Really. If you want to taste something, get some low-shelf bourbon or (even better) some incompletely rectified (raw) vodka. Sip this stuff, don’t pound it, and if you can find a small sample.

My Impression

I couldn’t get raw vodka, so I went with terrible low-shelf vodka, and even that doesn’t have the fusel-y notes I’m looking for like paint stripper. I actually don’t get much aroma from it at all, but the alcohol heat is absolutely noticeable. I think it is worth trying so you can associate yourself with the characteristics, but paint thinner will be your best bet for aroma. But, again, be careful.



How it is Perceived

Sulfur (more specifically we are talking about sulfur dioxide and hydrogen sulfide) is often characterized as rotten eggs or burnt match-like.

What Causes it?

Lager yeast strains are notorious for producing sulfur-like qualities, but these can age out with time. Sulfur can also be caused by autolysis, leaving a beer on yeast for so long that, eventually, the cell walls rupture and impart off-flavors. It can also be attributed to a young beer, so give it some more time before declaring it as ruined. Finally, low pitching rates and unhealthy yeast can cause this to occur.

Replicating the Flavor

Take 1/4 of a campden tablet, crush it up, and dissolve it in 1/4 ounce of beer. Now, using a teaspoon (or smaller), start adding this mixture to one of your prep glasses, mixing, and sampling. Add more as needed until you can perceive the sulfur qualities. Keep in mind that, according to MoreBeer, people with asthma and sulfite-sensitivity/intolerance should not consume this. So you can smell the mixture still and pick up those off-flavors, but don’t drink.

My Impression

I have asthma, and I drank this. I know I shouldn’t have, and for your safety I don’t think you should either, but here we are. I kept an inhaler next to me just in case, for the sake of safety, but full disclosure I went ahead and did it.

The smell was off, but it wasn’t quite “sulfur”. The flavor though definitely had sulfur notes, though not as I initially believed I’d have categorized them. I also had a bit of an asthma issue. Nothing to be worried about, but lungs tightened a bit so be on the lookout for that if you are prone to asthma issues. Not at all pleasant, but not as close to burnt=match as I would like. It could be that I didn’t use enough campden, or that this isn’t quite close enough to really replicate the flavor.

Light a match, blow it out, smell (which means waft, not straight up inhale), and note those burnt-egg characteristics. That is sulfur, and that’s what you should be on the lookout for.


Learn the off-flavors and not only will you be able to give other people more valuable feedback, but you’ll be able to identify the issues in your own beer. The flavors I’ve recommended here are not exact, but they are each a great starting point for identifying these common off-flavors. Special thanks to /u/rayfound of the /r/homebrewing community for this farmhouse amber, great way to remember that there is good beer in the world after drinking all of those samples.

Cheers everyone!


5 Common Off-Flavors and How to Fix Them

5 Common Off-Flavors and How to Fix Them Part II

How to Brew by John Palmer

Off-Flavors from the BJCP

Sulfur Compounds in Beer from MoreBeer

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