Stay at Home(Brew) Off-flavor: DMS

Stay at Home(Brew)
Off-flavor: DMS

During these times where we are at home for an extended period, homebrewing is seeing an uptick. Whether it be former homebrewers picking up the hobby once more, the avid upping home production, or those taking up the hobby for the first time it can be very rewarding. When homebrewing, one must take care to watch out for common off-flavors that could show up on your finished beer that could put and asterisk on your hard work. Let’s talk about DMS.

Dimethyl Sulfide, or better known by the acronym DMS, is a compound characterized by its distinctive creamed corn or cooked vegetable aroma and flavor. In some extreme cases, it may be reminiscent to rotten vegetables or dead shellfish. Very unappealing in those large quantities.

DMS isn’t always an off-flavor, though. In certain beer styles, a slight note of DMS is acceptable, if not welcomed, and sometimes expected to be there. The American lager family and Cream Ale are great examples of that. Other examples include Kölsch, Helles, German Pils, and other styles may also have a slight hint of DMS as well as other similar styles that may fit the bill.

With that said, it is not a required flavor and not all examples have it. It’s not a flaw if there’s a slight corny note in the background of these styles, although it is not necessarily essential. However, a large presence of DMS is always a flaw.

The origin of Dimethyl Sulfide is found in the grain used to make beer, barley. A compound known as S-Methyl-Methionine (SMM), an amino acid formed in barley during the germination stage of malting is the precursor to DMS. Once germination is completed and the barley begins to sprout, it is then heated, or kilned, to remove moisture. From there it can be kilned further to create a verity of malts. The lightest of kilned malts are only heated for a short while at about 170*F. Not enough heat or time to degrade much of the SMM.

The SMM is released into the wort during the mash but is not converted into DMS until it gets into the boil kettle. SMM is thermally liable and, as it turns out, boiling temperatures are enough to convert it into something else. And that something else is -you guessed it- DMS.

Homebrewers beware: During production, the steam created during wort boil caries a ton of DMS. You may experience a large amount of DMS if they cover their kettle to speed up the boil or to make it more vigorous. All the steam condensates on the lid and drips concentrated basically liquid DMS back down into their boiling wort. A long 90-minute boil is highly recommended. Leave your kettle uncovered!

Commercially, this is an important reason why fans and flues are used to carry the steam away into the atmosphere and not allowing it to condense back into the kettle. A broken or improperly working fan or flue causes the same effect as a covered homebrew kettle.

There’s another compound called Dimethyl Sulfoxide (DMSO) that is created when DMS is oxidized usually in the kettle. DMSO is not as volatile as DMS and is not heat sensitive, therefore, it would remain dissolved in the wort even after boiling. DMSO is then reduced into DMS in the fermenter by yeast during fermentation. There have been instances where this can kick-started during dry-hoping, so watch the oxygen exposure.

Since top-fermenting (ale) yeast usually produce a vigorous fermentation, the production of Carbon Dioxide (Co2) literally scrub away some of the DMS compounds out of the fermenter via the blow-off valve or airlock. On the other hand, bottom-fermenting (lager) yeast work much slower. More of the DMS created from DMSO during fermentation can remain in the beer because the Co2 production is not as energetic. This is yet another reason why pale lagers tend to have elevated levels of DMS compared to other styles.

The use of six row barley also tends to increase the production of DMS as well as some bacterial infections if sanitation becomes an issue. The addition of adjuncts such as flaked maize or corn sugar may enhance or confuse the perception of DMS in a finished beer. So that’s something else to keep in mind.

Support local homebrew shops:

Windsor Homebrew Supply Co.

743 Baker Street, Suite D, Costa Mesa

1045 N Armando, Suite E, Anaheim

Phantom Ales Pub & Home Brew Shop

1211 N Las Brisas St., Anaheim

O'Shea Brewing Co.

28142 Camino Capistrano #107, Laguna Niguel

Brewers Hardware (for large production)

5692 Buckingham Drive Huntington Beach

Cheers and happy homebrewing!

-Gilbert “Charlie” Perez, Advanced Cicerone®

The "D" Word: Diacetyl

Remember when we were young and we were taught never to say bad words? I apologize in advance for all the obscene language I'm about to say.

In the beer world, there's no greater profanity than saying the "D" word. And even worse is putting that "D" in your mouth. (Get your mind out of the gutter! ...That's not what I meant!)

I am referring to Diacetyl.

Pronunciation aside (die-ASS-a-teel, DIE-a-see-till, or die-assa-TEEL), this compound causes a movie popcorn, almost rancid butter-like flavor and aroma in beer. Although Diacetyl is produced by all yeast strains during normal metabolism, its quantities are greatly affected by many factors. The main factor is the amino acid Valine and how much of it is present in the wort. Regardless of this, Diacetyl is always produced at some rate during the first few days of fermentation.

*Warning! Chemistry up-ahead!*

2, 3-Butanedione (AKA: Diacetyl)

During the initial stages of fermentation, the yeast cell creates Valine as part of its metabolism cycle. Along this pathway to create the amino acid, the compound α(Alpha)-Acetolactate is also produced. A non-enzymatic oxidative decarboxylation of α-Acetolactate (I know, right?) occurs outside the yeast cell and is converted to 2,3-Butanedione, the compound we know as "Diacetyl."

The presence of Valine is directly related to the amount of Diacetyl produced because the enzyme that produces α-Acetolactate is deactivated when the wort contains high quantities of Valine. We know Valine is an amino acid and amino acids are the building-blocks of proteins. In turn, we can assume the high concentration of proteins in wort should significantly reduce the amount of Diacetyl produced. High protein levels could cause some other problems in the finished beer, so large protein quantities is not a viable solution to control Diacetyl.

Another compound called 2,3-Pentanedione is created via an separate pathway. This compound is also sent outside the yeast cell and will end up in the finished beer if not properly reduced. 2,3-Pentanedione is believed to have similar buttery flavor and aroma properties (sometimes described as honey-like), however this compound is not produced in very high quantities as 2,3-Butanedione is.

For you chemist out there, these two compounds are Vicinal Diketones. "In chemistry-speak, 'vicinal' essentially means 'adjacent', and 'diketone' means that there are two ketone functional groups (a ketone is an oxygen double-bonded to a carbon in the middle of a carbon chain)." (Beer Sensory Science)

As fermentation wraps up, most of the previously produced 2,3-Butanedione and 2,3-Pentanedione is reabsorbed by the yeast into its cell. Through more enzymatic activity, they are converted into 2,3-Butanediol and 2,3-Pentanediol, which have a much higher threshold for us humans. In other words, Diacetyl is turned into something we can't taste.

For you brewers out there, this is typically referred to as a "Diacetyl Rest." Brewers usually aid the reabsorption of these compounds by raising the temperature during the last day or two of fermentation. This rise in temperature excites the yeast and can more easily and vigorously convert Diacetyl into the non-flavored compound.

If Diacetyl is detected in your beer, it is usually an indicator of rushed production or improper fermentation practices.

Another common contributor to Diacetyl is a bacterial infection. The most likely culprits are the little bugs called Pediococcus and/or Lactobacillus. Both of these lovely bacteria create lactic acid and can produce Diacetyl as part of their fermentation products. While they may be a welcome addition to some wild ales and artisanal sour beers, it is quite unpleasant when found in dirty draft lines that haven't been maintained or cleaned sufficiently. Infections can also occur in many stages of the fermentation process, but dirty draft lines seem to be the biggest contributor for Diacetyl via bugs.

One more discovery is Diacetyl production during beer aging. Although the levels of Diacetyl in aged beer may be undetectable because of low levels or hidden behind the veil of oxidation compounds, Diacetyl could be nonetheless present.

In very small quantities, Diacetyl can be a contributing factor to the overall flavor and aroma profile of certain styles. Most English and Irish beers tend to have some detectable levels of Diacetyl adding a pleasant buttery undertone. An interesting fact is Diacetyl is one of the differentiating characteristics between a German Pilsner and a Czech Pilsner (Czech Pilsners are expected/accepted to have low levels of Diacetyl). However, in high quantities this compound can impart a butterscotch, movie popcorn, or a rancid butter flavor and aroma.

Another interesting fact to point out is while a great number of beer drinkers might be able to detect Diacetyl with ease, there are an equal amount of us that are completely blind to it. On that same note, some are very sensitive to Diacetyl while others will only find it detectable in extremely high quantities. Should you fall under any of these parameters, it is perfectly normal since it is simply genetics.

I think that's enough foul language for one lesson. I need to go wash my mouth out with some beer... Er, soap. And put a coin in the tip jar... Er, swear jar.



Class dismissed,

-Gilbert "Charlie" Perez, Certified Cicerone®




Photo Credits:
A big thank you to BeerAndBaking's Jessica Rice McNew for her amazing photography in this article!!

Resources:
-Beer Sensory Science
-Janux Chemistry of Beer Course Materials
-White Labs
-Oxford Companion to Beer

*Beer Education - Ale vs. Lager*

Ale and lager. Which of the two is better? Before we can even begin to think about how to answer this question, we must first have a clear understanding on the differences between ales and lagers. The answer is not as clear-cut and dry as one would think.

Perhaps the question we should ask is: What is an ale and what is a lager?

The short answer is... nothing! Well, that is if we consider only the end product, which is still beer. But if we dissect this, there are only a few differences. The main few are yeast species, fermentation temperature, aging temperature & duration, and fruit character.

Yeast

This is the only real physical difference between ales and lagers. There are two types of yeast that brewers choose from. Ale yeast (also known as "top-fermenting" yeast) is called Saccharomyces Cerevisiae. This species of yeast has many different strains. Lager yeast (also known as "bottom-fermenting" yeast) is called Saccharomyces Pastorianus. As with ale yeast, this species also has many different strains. They both act the same in terms of basic fermentation metabolism and end product. Reasoning for distinguishing them as bottom or top-fermenting seems to correlate with the amount of kräusen found at the top of the fermenter.

FYI: Kräusen is the fluffy stuff that develops at the top of the fermenter that is made up of yeast and proteins and other materials frothed up as a result of yeast metabolism.

Fermentation Temperature

In general, ale yeast is usually slated to ferment at higher temperatures (65°F to 70°F, on average with some strains reaching even higher) and thus results and a vigorous, relatively quick fermentation and development of a large cap of kräusen. Lager yeast typically ferment at cooler temperatures (48°F to 58°F, on average). Because of this cooler temperature, fermentation is less violent, takes much longer, and there is less kräusen.

Aging Temperature & Duration

Ales are generally not aged for very long and are usually cold crashed (significant drop in temperature to about +/-40°F) after fermentation to allow the yeast and proteins to drop out. Dry-hopping (adding hops into the fermenter after fermentation is complete) is done at this time. Typically, an average ale is ready in as little as two to four weeks.

Lagers ferment at cooler temperatures and therefore take longer to complete. Fermentation can last a few weeks and up to a couple months in some cases. Once fermentation has finished, lagering can start. The word "lager" is the verb "to store" or put away in German. Combined with cool fermentation, lagering at about 33°F helps to further clarify the beer and allows the flavors to round out. Lagers can take many months to complete, from brew-day to packaging. Depending on the beer, lagering alone can last upwards to 6 months to a year, although 3 months is average.

Fruit Character

The aforementioned items are production-based distinctions. All of those aspects result in the one piece of evidence we can detect in both flavor and aroma: Fruit character. Ale yeast produce many fruity esters due to the quick fermentation, generally higher temperatures, and short aging. This is acceptable and desirable. Lagers on the other hand, are clean and show no fruit character. The slow fermentation caused by low temperature and long lagering times result in a malt and hops focused beer.

There will be more explanation further below, but the same can be true with beers fermented cold with ale yeast strains, which will produce very little esters. Interestingly enough, lager strains used to ferment beers at ale temperatures will indeed produce more fruit esters than they would usually do if fermented cold.

Bonus: Myths About Ales and Lagers

"Lagers have lower alcohol than ales." ...FALSE!

Being an ale does not necessarily indicate a higher ABV. True, the high-alcohol beers are usually an ale of some kind, there are also lagers available that can reach ABV's above 10%. Eisbock is one example.

"Ales are dark." ...FALSE!

Cream Ales and American Blonde Ales are quite pale in color.

"Lagers are always light in color." ...FALSE!

Doppelbock, Dunkle, American Dark Lager, and Baltic Porter are examples of lager beers that are dark brown to almost black in color.

"Lagers have more carbonation." ...FALSE!

Have you ever popped opened a bottle of Duvel? That's a Belgian Golden Strong Ale. Try to pour it without a producing a foam head at least 3 fingers high. Just try it.

Curveballs

This is probably the most important part of this article. We have hybrid beers out there to throw us a off-course and shows off how far we have come in our understanding of what used to be a clear line between ale and lager. These hybrid beers are a blend of ale and lager, usually using lager yeasts fermented at the lower end of ale temperatures and/or often involve lagering for a period of time regardless of yeast strain or species. Examples of these hybrids include Cream Ale, California Common, Kölsch, and Altbier.

California Common and  Cream Ale use an adapted lager strain to ferment at the low-end of ale temperatures (too high for some lager strains) and results in clean lager characteristics. This is historically true for Cream Ale, but is currently not that common. Kölsch and Altbier are examples of an ale yeast strains fermenting at the high-end of lager temperatures (too low for some ale stains) used to produce lager characteristics. They also go through a period of cold conditioning although the duration varies by style. Those are some examples of styles which create clean, lager-like beers using non-traditional methods.

A word on lagering: It is not uncommon for a beer fermented with ale yeast to undergo a cold-conditioning phase or for a "bottom-fermented" beer to be aged at room temperature. The resulting beer may differ from the traditional expectations, but could still be enjoyable if done correctly.

Other cuveballs are beers fermented with other organisms and/or wild yeasts. These organisms and wild yeasts (such as wild Saccharomyces, Brettanomyces, Lactobacillus, Pediococcus, and Acetobacter) all have their own properties in regards to optimum fermentation temperatures. However, most of the beers we see inoculated with any type of "bug" or "wild" yeasts/organisms are typically kept at room temperature (68°-72°F) or higher. So, by the explanation above, these wild and sour beers are widely accepted as ales.

And there you have it!

To recap, ale yeast (Saccharomyces Cerevisiae) and lager yeast (Saccharomyces Pastorianus) is the only physical difference between them. The flavor differences between lagers and ales are small, but noticeable. Lagers are clean, little no no yeast character with and no fruity esters, fermented a cool temperatures, and are submitted to extended lagering. Ales tend to have fruit character, fermented at higher temperatures, and not aged as long by comparison. There are exceptions with hybrid's using lager strains at low ale temperatures or ale strains at high lager temperatures.

Hope you learned a thing or two. Thanks for reading!

Cheers,

Gilbert "Charlie" Perez, Certified Cicerone®

Beer Science: Skunk!

"This beer tastes like a skunk!!!"

Do I have your attention? It should because this is possibly the only recognizable off-flavor and aroma that's easily identified by the novice beer drinker and expert alike.

I’m sure a lot of us don’t really care if a beer is in a clear growler or a green bottle. That’s fine. But, in case you want to know why you get the whiff of an overly in-love cartoon character, then read on for some clarification.

How does a beer become skunked, anyways? Well, I’ll explain this in two ways: the simple way and the scientific way (between the sets of ** below).

The short answer is as follows: Your beer will be Light-Struck, or “skunked,” when visible blue or UV light comes in contact with the hop acids in the beer. The acids are broken down, rearranged, and transform into something called 3-MBT. In other words, the hop acids become skunk spray! Well, something very close to it.

When exposed to light, this process begins to take place instantaneously. If you’re drinking your beer outside, it may not be perceived until the end of your pint, if at all, but it WILL happen.

**

Warning: Chemistry explanation begins here. Scroll down to the past the ** below to skip.

Ok, here we go. I hope you’re sitting down for this one.

First, let’s start by identifying what is needed to skunk a beer:

1. Isomerized Humulone Alpha Acids,

2. Riboflavin.

3. Light, including the Visible Spectrum and Ultraviolet.

1. Hops contain Alpha Acids (known as Humulone(s) communally) that need to be Isomerized (transformation of a molecule into another while keeping the same number of atoms) in order to provide the necessary bittering properties to beer. This is accomplished when hops are boiled in the brewing process. These Isomerized Alpha Acids become Isohumulones. On a side note, Isohumulones add antibacterial properties to beer.

2. Riboflavin is a B-Vitamin naturally produced by the vast majority of Saccharomyces Cerevisiae (Ale Brewing Yeast) strains during fermentation. The higher the malt content, the higher the Riboflavin present in beer.

3. Visible light and UV with wave lengths between about 350 and 500nm is of concern here.

Now that we have the suspects in custody, let’s recreate the crime.

When visible light strikes beer, the Riboflavin is agitated and takes an electron from the Isohumulone, changing the chemical structure of the molecule. The Riboflavin then reacts with an amino acid containing sulfur to create a sulfhydryl radical. This radical then combines back to the already modified Isohumulone molecule to create “3-methylbut-2-ene-1-thiol,” or 3-MBT. This is what gives the “skunky” flavor to the beer. Its structure is basically the same to that of skunk spay. Yum!

The threshold of human detection for 3-MBT is surprisingly low (easily perceived at about 4PPT in beer) and is one of the most recognizable off-flavors in beer. We've all had beers out of clear or green bottles at some point, right?

**

I’m not taking sides or trying to prove anyone right or wrong, I’m simply stating the facts. You have a clear growler of fresh beer? Fine, just keep it away from light as much as you can. We can’t help the marketing decisions some establishments make. All we can do, as craft beer enthusiasts, is do OUR best to enjoy the beer as the brewer intended.

Obviously, clear or green bottles/growlers allow for easy formation of 3-MBT while brown bottles provide just about enough protections. Kegs and cans (yes, cans!) are the way to go since they block 100% of light, preventing this issue all together... Until you pop it open and pour it out under the sun. You’re on your own, there.

Bottom line, know what to expect and the real possibilities of some off flavors if you have a beer in a clear glass or in sunlight. The odds are you will have a skunked beer at some point. However, the hop content may be low enough that you might not even notice or you’ll finish your beer before it becomes really noticeable. Take the proper, simple precautions and you’ll be fine.

In the end, it's all about enjoying your beer. So do just that, however that may be.

Cheers!!

-Gilbert "Charlie" Perez, Certified Cicerone®

Source/More Info: http://beersensoryscience.wordpress.com/2011/03/17/lightstruck/