Why Does The Sea Smell Like The Sea?

A microbiologist explores the distinctive odors of a day at the beach.

Sea Smells

Victor Kerlow

As I took a deep breath in, a familiar scent filled my nose: slightly sulfury, with just a pinch of green, and a briny finish. It was the smell of the seashore, but I wasn't actually at the seashore. On the contrary, I was standing in a cheese cave in the frozen northeast kingdom of Vermont, it was December, and I had my nose in a Petri dish full of yeast.

At that moment, separated from the physical seashore by 150 miles, I began to ponder what actually accounts for the telltale flavors of the sea. People often describe the taste of uni as a meaty, in-your-face beach flavor. Nori has that green sea taste. And oysters are best when they append the bright brininess of their growing environment with their own sweet butteriness. What are the chemicals that actually create these ocean flavors?

No single chemical compound can really be pinned down as quintessential ocean essence. A diverse mix of molecules contribute to that seemingly singular seashore flavor that you smell at the beach, and that you taste in many of the foods harvested from the ocean. Here’s an overview of three of the more widespread marine molecules, brought to you by death, sex, and fish food.

Dimethyl sulfide

Seashore funk

One of the most common and best-understood components of seashore aroma is dimethyl sulfide, or DMS. Food scientists use a variety of descriptors to characterize the flavor notes of DMS, including green, sulfur,_ clammy_, boiled cabbage, and creamed corn. This stinky sulfur compound puts the funk in everything from nori, to truffles, to beer. It's also abundant in farts.

In the ocean, DMS is produced in large part by bacteria that eat dying phytoplankton—microscopic organisms that use light from the sun to make their own energy. The phytoplankton use a precursor to DMS known as dimethylsulfoniopropionate (DMSP) as a sort of sunscreen to protect themselves from the stresses of being phytoplankton (it’s rough out there!). When the phytoplankton die, they burst open and the bacteria make DMS from DMSP as they digest the phytoplankton. Seabirds and other ocean animals use the smell of DMS to identify areas rich in phytoplankton, which are also usually packed full of tasty fish.

For a clearer idea of what DMS smells like, visit a salt marsh. The flooded soils of salt marshes release a whole bouquet of sulfur smells, and one is DMS. Barring that, your local artisan-cheese counter is one of the best places to get a nice hit of DMS. Microbes such as the bacterium Brevibacterium and the fungus Geotrichum that grow on ripening cheeses can produce high levels of DMS as a consequence of decomposing cheese proteins. If I had to guess, I'd say that DMS played a part in producing the ocean aroma I encountered from that cheese sample in Vermont.

Dictyopterenes

The smell of seaweed sex

Sex has a smell, even for seaweed.

In the 1960s and ’70s, scientists isolated chemical compounds from numerous seaweeds that had a strong “beach odor.” When they started trying to figure out the role of these compounds, they noticed that the seaweed eggs were producing a lot of these volatile compounds and seaweed sperm were highly attracted to them. With all of the various species of sperm swimming around in the ocean, it’s good to have a chemical calling card to lure in compatible mates.

Dictyopterenes, a type of these aromatic sex pheromones, also contribute to the aroma profiles of edible seaweeds. I've never actually smelled a purified version, but most reports describe it as smelling like—surprise!—dried seaweed. Limu lipoa (Dictyopteris plagiogramma), a seaweed commonly eaten in Hawaii, is packed with dictyopterenes, and lends a wonderful ocean spice often used in stews. A perfect dish to get you in the mood.

Bromophenols

Fish are what they eat

The brininess of wild seafood, including fish, mollusks, oysters, clams, shrimp, and crabs, comes in large part from a class of compounds called bromophenols. In low concentrations, these chemicals are described as smelling sealike, fishlike, and crablike. In really high concentrations, they come off as a harsh chemical smell, similar to iodine.

Seafood biologists suspect that most of these animals don’t produce these compounds on their own, but acquire them from the foods they eat, especially marine worms, algae, and other bottom-feeders. Wild-caught seafood tends to have higher concentrations of these compounds and more oceanlike flavors compared to their farm-raised counterparts. Some fish species, like Pacific salmon, which split time between the ocean and fresh water, exhibit high levels of bromophenols when they’re caught in the ocean and almost none when landed in fresh water.

In order to re-create the flavor of ocean-faring fish, some farmers have attempted to add bromophenols to the diets of farm-raised seafood. They’ve had mixed success. One challenge with this approach is striking the delicate balance between a hint of ocean flavor and the overbearing metallic tang of iodine. You can take a fish out of the ocean, but it’s hard putting the ocean back in the fish.

Benjamin Wolfe will be an Assistant Professor of Microbiology at Tufts University starting in September 2014. He can't decide what to wear on his first day of school. Twitter: @LupoLabs

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