Modernist-Cuisine-Vol.-1-Small

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For more on proper freezing techniques for fish,
see Freezing, page 186.
Tapeworms, also called
cestodes, have sucker-like parts
on their heads that they use to
anchor themselves to the
intestinal walls of their hosts.
trichinellosis and the cooking temperature
needed to prevent it. Such overstatement may
have arisen from good intentions, but at some
point misleading recommendations become
irresponsible.
Freezing also kills trichinae in pork. For this
reason, virtually all pork and pork products sold in
the U. S. have been frozen, even if they are labeled
“fresh” at the store. Unfortunately, freezing is no
surefire way to eliminate trichinae in wild game.
Bears, for example, hibernate in the winter, so
their muscle cells contain special proteins that
prevent the formation of ice crystals, and some
health authorities fear that those proteins may also
protect encysted Trichinella larvae from low
temperatures. As a result, freezing may not be
a reliable means of killing the worms in bear meat.
A separate family of parasitic worms, known as
nematodes or anisakids, includes species such as
Anisakis simplex and Pseudoterranova decipiens
(which is also listed under the genus Terranova or
Phocanema). These worms follow a life cycle that
resembles that of trichinae but in a marine
environment.
Adult anisakids infect marine mammals such as
whales, dolphins, and seals. Eggs in the animals’
feces pass into the ocean, where the newly hatched
larvae infect copepods, or tiny shrimp-like
crustaceans. Fish or squid then eat the infected
copepods, other marine mammals next eat the fish
or squid, and the cycle continues.
Humans who eat fish provide the anisakids with
a ready stand-in for marine mammals. The human
gut is, however, sufficiently different that the
worms cannot mature, so they generally die after
a week or so in the human body. Such an infection
can, in the meantime, generate quite a stomachache,
with symptoms so severe that physicians
sometimes misdiagnose the condition as appendicitis.
A strong allergic reaction to the worms,
although less common, could culminate in
anaphylactic shock.
Raw fish poses the biggest risk of infection
because cooking fish to an internal temperature of
60 °C / 140 °F or more for at least one minute kills
the worms. Several food safety guides assert that
15 seconds at an interior temperature of 63 °C /
145 °F will also do the trick. Those temperatures,
however, are high enough to overcook the fish, at
least to many people’s taste.
Not surprisingly, sushi-loving Japan is the
epicenter of foodborne anisakid infections, also
known as anisakiasis. Tokyo alone tallies about
1,000 cases annually, most of which are from
home-prepared sushi and sashimi. Only rarely are
sushi bars with professional sushi chefs implicated.
The U.S. reports fewer than 10 cases a year.
Anisakid infection occurs more frequently in
certain fish species that fishermen catch near the
shore, such as salmon, mackerel, squid, herring,
anchovies, and rockfish, than it does in other
species. Coastal fish are more likely to eat infected
copepods that regenerate in seals and other
marine mammals. Farmed salmon do not eat
copepods and are therefore generally anisakidfree,
as are wild tuna and other deep-ocean
species.
Wild salmon, however, are especially prone to
infection. In 1994, for instance, an FDA study
found anisakids in 10% of raw salmon samples
that were obtained from 32 sushi bars in the
Seattle area. Despite this alarming statistic,
human anisakiasis cases are still relatively rare
because most ingested larvae die or pass harmlessly
through the intestinal tract.
The technique traditionally used by chefs to
detect worms requires them to hold fish fillets up
to a light and inspect them visually, a procedure
called candling. Master sushi chefs say they can
feel the worms with their fingers. And although
some chefs can indeed find a few worms through
candling or handling, studies suggest that others
may be easily missed, especially in salmon or
mackerel. No matter how experienced the sushi
master, then, neither method is fully reliable.
Freezing kills anisakids, and in this way the
food industry ensures that worms pose no health
risk in fish that is served raw. For commercial
retailers, the FDA recommends freezing and
storing the fish in a blast freezer for seven days at
−20 °C / −4 °F, or for 15 hours at −35 °C / −31 °F.
Most sushi is, in fact, frozen before it is served; the
1994 FDA study found that all but one of the
anisakid worms spotted in the Seattle sushi were
dead or dyingcasualties of the freezing process.
If done improperly, however, freezing can negatively
affect the taste and texture of the fish.
Other notable nematodes include the giant
intestinal roundworm, Ascaris lumbricoides, which
can grow to 41 cm / 16 in. It causes ascariasis, the
most common parasitic worm infection in the
world. Investigators have linked ascariasis to
cabbage and other raw produce that was grown in
contaminated soil and to improper food handling
in tropical regions and rural parts of the southeastern
United States. The roundworm migrates
through the lungs to the small intestine, where it
can live for up to two years.
Flukes and Tapeworms
Among foodborne parasites, flukes don’t get a lot
of public attention. But concern about species such
as Fasciola hepatica has grown among public
health authorities throughout western Europe
especially France, Spain, and Portugalas well as
in the Americas. Commonly known as the sheep
liver fluke, the leaf-like worm counts sheep, goats,
and cattle among its principal hosts, although it
can also make its way into humans through the
fecal-oral route.
One of the larger parasitic worms, F. hepatica
can grow to 2.5 cm / 1 in; its aptly named cousin
F. gigantica can reach lengths three times as long.
As part of the fluke’s complicated life cycle,
embryos that are released in egg-laden animal
feces infect freshwater snails, in which they
develop into mature larvae before dispersing again
as cysts that glom onto aquatic vegetation.
Humans who eat raw or undercooked watercress
or food that has been washed with contaminated
water can accidentally ingest these cysts
and contract a potentially serious invasive
infection known as fascioliasis. Immature worms
first migrate through the liver, causing fever,
inflammation, and abdominal pain as they go.
Eventually they make their way to the bile ducts,
where a progressive buildup of the parasites can
in time block the ducts. Other species of liver
fluke are endemic to Asia and Eastern Europe,
Tapeworms can persist in raw,
smoked, and dried foods but are
killed by freezing (for 48 hours at
−18 °C / −0.4 °F), by hot-smoking
(for 5 min or more at 60 °C / 140 °F),
or by using standard cooking
recommendations.
A live anisakid emerges from a piece of
halibut we bought at a reputable, high-end
organic grocery store near Seattle.
122 VOLUME 1 · HISTORY AND FUNDAMENTALS
MICROBIOLOGY FOR COOKS 123