The distinct scent of the sea or the strong aroma of cooked cabbage might seem unrelated, yet a single chemical compound is largely responsible for both. Dimethyl sulfide, or DMS, is a naturally occurring organosulfur compound that plays a role in various smells encountered in daily life.
Characterizing the Odor of Dimethyl Sulfide
Dimethyl sulfide possesses a multifaceted odor profile that varies significantly with its concentration. At higher levels, it commonly presents as a pungent, sulfurous smell, often described as resembling cooked or rotting cabbage. As its concentration decreases, the perception shifts, revealing nuances of creamed corn, asparagus, or even a general sweet-corn character. Humans have a remarkably low detection threshold for DMS, meaning even minute amounts can be perceived. This sensitivity allows us to detect its presence in diverse settings, influencing our sensory experience of many natural and processed substances.
Natural and Anthropogenic Sources
In marine environments, DMS is a breakdown product of dimethylsulfoniopropionate (DMSP), a compound produced by microscopic ocean algae called phytoplankton. When these phytoplankton are consumed by zooplankton or undergo cell lysis, bacteria in the seawater convert DMSP into DMS gas, which then escapes into the atmosphere, creating the characteristic “smell of the sea.” DMS also naturally occurs in other settings, such as marshes and soils, due to bacterial activity, and is a volatile component found in truffles.
DMS contributes to the aroma of numerous cooked foods, including corn, cabbage, asparagus, beetroot, and various seafoods. This compound also forms during the fermentation processes of certain products, such as beer. In brewing, DMS originates from precursors like S-methyl methionine (SMM) and dimethyl sulfoxide (DMSO) found in malt, which are converted during heating and microbial activity. Beyond natural occurrences, industrial processes like the Kraft process, used in paper pulp mills, release significant amounts of DMS. These emissions, along with those from some food processing plants, contribute to the compound’s presence in the atmosphere through human-related activities.
The Role of Dimethyl Sulfide in Ecosystems
Certain seabirds, including petrels and albatrosses, utilize the scent of DMS as a foraging cue. These birds have evolved to detect DMS plumes rising from the ocean surface, which indicate areas where phytoplankton are being grazed by zooplankton. This chemical signal guides them to rich patches of their prey.
DMS also influences atmospheric processes and potentially global climate through its role in cloud formation. Once released into the atmosphere, DMS undergoes oxidation, forming sulfur-containing compounds like sulfuric acid. These sulfuric acid particles can then act as cloud condensation nuclei (CCN), serving as microscopic “seeds” around which water vapor condenses to form cloud droplets. An increase in these nuclei can lead to more numerous and brighter clouds, reflecting more sunlight back into space and influencing the Earth’s radiative balance. This proposed feedback mechanism, known as the CLAW hypothesis, suggests a link between oceanic biological activity and atmospheric conditions.