This Month’s Question: My beer sometimes has a corn-like sulfury smell. What can I do about it?
Answer: A corn-like smell is usually due to a specific chemical compound called dimethylsulfide, or DMS for short. DMS forms in the malting process and in the boiling process while brewing any beer. It is the result of a thermal degradation of sulfur-containing amino acid in the grain called s-methylmethionine. This amino acid is present in all malts. Hence, all beers have some amount of DMS.
DMS is a highly volatile compound. This makes it an easily detectable compound in aroma, even in trace quantities. Fortunately, the volatility makes it fairly easy to scrub out of your beer.
The amount of DMS in your finished beer depends on a number of factors. First of all is the amount of s-methylmethionine in the grain. High protein malts such as six-row have higher amounts, hence more DMS. Some of the DMS is driven off by heat in the kilning process. Hence, the paler malts kilned at lower temperature have more. These two factors combined contribute to the fact that pale lagers (made from pale six-row malt), often have high levels of DMS. Not surprisingly, corn also contains a lot of s-methylmethionine. These characteristics are a hallmark of lager beers. A lager without DMS tastes rather bland.
The second factor that affects the amount of DMS is how much is removed from the wort during the boil. Every bubble of steam that comes out of the kettle will carry some DMS with it. Hence, longer boiling times and a more vigorous boil tend to reduce DMS levels. For best results, you want to keep the boil rolling for the whole time. Don’t simmer your beer! Read more