Beer Sensory Skills 101 | Malt | DMS

The Chemistry:

Dimethyl sulfide (DMS) is a sulfur-containing compound that can contribute to vegetal-like off-flavors in beer. The chemistry behind DMS begins with the precursor compound S-methyl-methionine (SMM), which is naturally present in malted barley and malt extracts. During the malting process, precursor compounds like SMM are formed as part of the biochemical reactions that occur in germinating barley grains. When malted barley is mashed and boiled during the brewing process, SMM is released into the wort. Under heat, SMM undergoes thermal decomposition, leading to the formation of DMS. This process involves the cleavage of the S-methyl group from SMM, resulting in the release of DMS. The chemical reaction can be represented as follows:

S-methyl-methionine (SMM) → Dimethyl sulfide (DMS) + Other Byproducts

Once formed, DMS is volatile and can evaporate from the wort during boiling. This is why it's crucial to achieve a vigorous boil during the brewing process, as it helps drive off DMS vapors and reduce their concentration in the finished beer.

After boiling, DMS levels can continue to decrease during fermentation and conditioning, as the compound is further volatilized and expelled from the beer. Proper fermentation conditions, including temperature control and yeast health, can help minimize the risk of DMS-related off-flavors developing during this stage.

Overall, understanding the chemistry behind DMS formation is essential for brewers to effectively manage its presence in beer and ensure a clean and flavorful finished product. By following best practices during brewing and fermentation, brewers can mitigate the risk of DMS-related off-flavors and produce high-quality beer.

DMS in Extract Brewing:

Dimethyl sulfide (DMS) can be an issue in extract brewing, although it is generally less common compared to all-grain brewing. In extract brewing, DMS is typically produced during the hot-side brewing process, particularly during the wort boiling stage. It is formed from precursor compounds called S-methyl-methionine (SMM), which are present in malted barley and malt extracts. During boiling, SMM is converted to DMS, which is then vaporized and removed from the wort.

Please keep in mind that DMS is not an issue with most of our Coopers/MRB hopped malt extract kits, recipes, and refills because they do not require a boil, nor do they contain the precusor compounds that form DMS. However, if you are brewing a recipe that uses an extended boil, supplementary grains, or non-Coopers/MRB malt extracts, it is still essential to understand this off-flavor, how it is formed, and how to prevent it. This is also important if you plan on moving beyond extract brewing into the world of all-grain brewing.

To minimize the risk of DMS in extract brewing, it's essential to follow best practices during the brewing process:

• Vigorous Boiling: Ensure that you achieve a vigorous rolling boil during the wort boiling stage. A vigorous boil helps to drive off DMS vapors and reduce their concentration in the finished beer.

• Extended Boil: Consider extending the duration of the wort boiling stage to further reduce DMS levels. A longer boil can help ensure complete conversion of SMM to DMS and enhance DMS volatilization. Just be sure to take evaporation into account and add extra water, if necessary.

• Covered Boil: It is recommended to boil the wort with the kettle partially or fully uncovered to allow DMS vapors to escape.

• Chilling Quickly: After the boil, rapidly cool the wort to pitching temperature to halt enzymatic activity and prevent the formation of additional DMS. A rapid chill helps lock in the desired flavors and minimizes the risk of off-flavors.

• Fermentation: Ensure proper fermentation conditions, including temperature control and yeast health, to minimize the risk of off-flavors developing during fermentation.

While DMS can be a concern in extract brewing, following these best practices can help mitigate its impact and ensure a clean and flavorful finished beer. Additionally, using fresh, high-quality malt extracts and maintaining sanitary brewing practices can further reduce the risk of off-flavors in extract brews.

Dimethyl Sulfide Molecule

Aroma:

• Cooked Cabbage: At high concentrations, DMS can produce a distinct cabbage-like aroma, reminiscent of cooked or boiled cabbage.

• Cooked Corn: DMS can create an aroma reminiscent of cooked or canned corn. This aroma is often described as sweet and slightly vegetal, resembling the smell of boiled or steamed corn kernels.

• Vegetal: In addition to cabbage and cooked corn, DMS can produce vegetal aromas similar to boiled or steamed vegetables. These aromas may include notes of cauliflower or green beans.

• Sweet Corn: At lower concentrations, DMS can contribute to a subtle sweetness and richness reminiscent of fresh corn on the cob. This aroma may be perceived as pleasant in moderation but can become undesirable at higher levels.

• Sulfur: In some cases, DMS may impart a sulfur-like aroma to beer, similar to the smell of rotten eggs. This sulfur character can vary in intensity and may be perceived as unpleasant or offensive.

Flavor:

• Cabbage-like Undertones: At times, DMS may impart a distinct cabbage-like flavor to beer, reminiscent of cooked cabbage. This vegetal note adds to the complexity of the beer's flavor profile, but excessive levels can be undesirable.

• Corn-like Sweetness: DMS can lend a flavor reminiscent of cooked or canned corn, presenting a sweet and somewhat vegetal taste similar to boiled or steamed corn kernels.

• Vegetal Notes: DMS can contribute vegetal flavors akin to boiled or steamed vegetables, with hints of cauliflower or green beans.

• Subtle Sweetness: At lower concentrations, DMS may add a subtle sweetness and richness to beer, resembling the taste of fresh corn on the cob. While this flavor can be pleasant in moderation, it may become undesirable if too prominent.

• Sulfur Undertones: In certain instances, DMS might contribute sulfur-like flavors to beer, reminiscent of rotten eggs or cooked cabbage. The intensity of these sulfur notes can vary and may be perceived as unpleasant or off-putting.

Overall, the flavors associated with DMS in beer encompass a spectrum from sweet and subtle to pronounced and vegetal, influenced by various brewing factors. Careful management of DMS levels during brewing is essential to achieve the desired flavor profile in the finished beer.

Sensory Training:

• Aroma Identification: Familiarize yourself with the aroma of DMS by sniffing samples of beer known to contain the compound. Look for beers with a cooked corn or vegetable-like aroma, as these are common descriptors for DMS. You can also create a reference sample by intentionally contaminating a small amount of beer with DMS for training purposes.

• Conduct Comparative Tastings: Conduct side-by-side tastings of beers with varying levels of DMS to train your palate to detect differences in aroma and flavor. Start with a beer containing low levels of DMS and gradually increase the concentration with each sample. Take note of the intensity and character of the DMS aroma and flavor in each beer.

• Aroma Training Exercises: Engage in aroma training exercises using common household items or food ingredients that share similar aromas with DMS. For example, sniffing cooked corn, cabbage, or canned vegetables can help reinforce your olfactory memory and improve your ability to recognize DMS aromas in beer.

• Tasting Grids: Create tasting grids or scorecards to systematically record your observations during beer tastings. Include categories such as aroma, flavor, intensity, and overall impression, and use descriptive language to document your sensory experiences with DMS.

By employing these techniques and incorporating regular practice into your beer-tasting routine, you can enhance your ability to detect and identify DMS in beer without relying on external feedback from other individuals. Consistent practice and self-guided exploration are key to developing and refining your sensory analysis skills over time.

While dimethyl sulfide (DMS) is generally considered an off-flavor in beer, there are some beer styles where its presence may be acceptable or even desirable, depending on the brewing tradition and flavor profile of the beer. Cream ales, for example, are known for their smooth and balanced flavor profile, which may include subtle corn-like sweetness. A hint of DMS can complement the malt sweetness in cream ales, adding depth and complexity to the beer's flavor profile. Here are a few beer styles where DMS may be more tolerated or intentionally incorporated:

It's essential to note that the acceptability of DMS in beer can vary widely depending on regional preferences, brewing traditions, and individual taste preferences. While DMS may be tolerated or even embraced in certain beer styles, excessive levels of DMS can still detract from the overall quality and enjoyment of the beer. Brewers should strive to manage DMS levels carefully and balance its presence with other flavor components to achieve a well-rounded and harmonious beer.