Why
Does The Sea Smell Like The Sea?
A microbiologist explores the
distinctive odors of a day at the beach.
By Benjamin
Wolfe in Popular Science magazine
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.
Lucky Peach is a quarterly journal of
food and writing. Each issue focuses on a single theme, and explores that theme
through essays, art, photography, and recipes.
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