How We (Usually) Don’t Get Sick From Raw Sushi

Here?s the difference between delicious sushi, and dangerous undercooked chicken or hamburger

I certainly did not write this article just so I could share all these incredibly cute animations by Marcus Gestr and Brikk studio? Source.

It?s almost anathema for me to admit it, living in the Bay Area, but it took me some time to come around on sushi.

Part of this uncertainty came from growing up in the Midwest, where there wasn?t much opportunity to really enjoy fresh fish. After all, any salt water fish, like tuna or salmon, will have to travel quite a ways to get to Minnesota ? and does anyone really want to risk dodgy, gas station sushi?

It wasn?t until I started graduate school, out on the West Coast in California, that I started trying really good, really fresh sushi ? and I was hooked. The good stuff is fresh, with a great flavor; it?s not ?fishy? in the same way as cooked fish, but has a milder flavor that pairs great with the umami of soy sauce and wasabi.

(Don?t even get me started on the first time I tried wasabi, by the way. You know the story, I?m sure you?ve heard it before ? thought it was some sort of avocado-based paste, like guacamole, put way too much in my mouth, and then spent the next several minutes gasping and gulping water.)

But there?s still a little part of me that finds it weird, eating raw fish. When I was a child, it was drilled into my head that we don?t eat any meat that isn?t fully cooked. Yet somehow, sushi is the exception to the rule?

Raw chicken? Wash every surface that it touches, to avoid spending several days incapacitated with salmonella.

Raw fish? Go ahead, put it in your mouth!

And even among fish, it seems like there are some hidden, inscrutable rules. Why is it okay to eat tuna and salmon when raw, but why not pike, or tilapia? What makes these few fishy examples okay to eat raw?

Two Threats, Two Methods of Neutralizing Them

There?s two big concerns when thinking about parasites in meat ? the bacteria, and the other types.

First off: the bacteria. There?s a whole host of different, potentially toxic bacteria that live in the animals we eat, mostly in their digestive systems. This includes pathogenic (disease-causing) strains of Escherichia coli, various species in the Salmonella genus, and others.

These bacteria aren?t found in the muscle tissue of these animals ? that is, not in the stuff that we eat. Instead, they?re located almost entirely in the lower digestive tract, everything that comes after the stomach.

The challenge here comes when preparing the meat ? in less squeamish terms, when slaughtering the animal. When fish are harvested, they?re gutted early on, removing the digestive tract and keeping the meat fairly free of these bacteria.

On the other hand, in most slaughterhouses, the bacteria from the intestinal tracts of the killed animals end up being spread over the rest of the meat, which is why that chicken breast from the store is likely contaminated with Salmonella ? even though there was no Salmonella on that part of the bird while it was alive.

The second danger, when it comes to eating meat, are pathogens of a different sort. These are larger, multicellular, and can have complex life cycles. These larger pathogens include nematodes (flatworms), roundworms, or even Cnidarians (multi-celled parasites, distantly related to sea anemones).

These organisms, unlike the bacteria, aren?t confined to the intestinal tract. Instead, they live out a complex life cycle, where different stages of growth take place in different hosts.

In the case of fish, the parasites will burrow into the muscle of the animal, where they?ll form cysts (little fluid-filled pockets). Sometimes, this cyst contains eggs; more often, it?s where the adult parasite hangs out and waits for the fish to be consumed by a predator ? leading the parasite to the next stage of its life cycle.

The bad news about these parasites? They?re nasty, sometimes hard to diagnose, and the tiny, difficult-to-spot cysts in the muscle tissue can be smaller than a grain of rice.

The good news? We?ve got a great way to kill them ? freezing.

When you eat ?fresh? sushi, you?re almost certainly eating frozen fish ? and that?s a good thing.

That?s right. Unlike bacteria, which just go into hibernation when frozen, these parasites can?t stand the bitter cold. When frozen, their cells burst, and they go from dangerous parasite to harmless bit of popped cells in the fish.

And this freezing isn?t just a suggestion. In the United States, the FDA mandates that all fish served to consumers ? even, and especially including sushi ? must be frozen at some point, in order to get rid of any parasites that may be lurking in that fish muscle.

The FDA says that fish may be frozen in any one of the following ways:

-4F (-20C) or below for 7 days (total time)
-31F (-35C) or below until solid, and storing at -31F (-35C) or below for 15 hours
-31F (-35C) or below until solid and storing at -4F (-20C) or below for 24 hours

Most of the time, this freezing happens even before the fish reaches the shore; on the fishing boats, the fish are flash frozen at -40 degrees Fahrenheit so that they can be preserved and stored until the ship reaches the shore. When you eat ?fresh? sushi, you?re almost certainly eating frozen fish ? and that?s a good thing.

Unfortunately, there?s one big issue: the FDA has this as a guideline, but does not enforce this requirement.

This means that, in some cases, restaurants assume that suppliers have handled the freezing, while suppliers assume that the distributors will do the freezing, while distributors assume that the restaurants will do it?

This has led to some regions, like New York City, implementing laws that require the fish to be frozen before being served ? and for proof to be provided. And in turn, this led to some uninformed sushi consumers getting upset that their fish might have to be frozen ? not realizing that it?s happening already, and it?s a good thing.

Blind taste tests have shown that frozen fish doesn?t taste worse than fresh ? and it may even be better. Flash freezing, right after the fish is caught, helps to lock in the flavor and ensure that you get a fish that doesn?t taste like it?s been sitting around in transit for weeks.

Better taste, and parasite free? Sign me up for flash-frozen sushi.

So, why can we eat raw fish, but we can?t eat raw hamburger or chicken?

The first reason is microbial: when we clean raw fish, it?s easier to remove the bacteria-filled intestines that could otherwise contaminate the meat with pathogenic microbes. (Note that easier doesn?t mean that there are never microbes that contaminate the meat; outbreaks of Salmonella have been traced to sushi.)

The second reason is parasitic: the ?fresh? sushi that you eat has often been through flash freezing, which kills larger parasites, like nematodes or roundworms, that may have formed cysts in the muscle tissue of fish. All sushi should go through this flash freezing process to kill any parasites that may be lurking within ? it doesn?t impact your enjoyment, or the taste, of the fish.

One last note: what about beef tartare, or a rare steak? It turns out that, while salmonella can permeate the meat of chicken (reaching the inside), the E. coli that can be found on beef tends to stay on the surface. This allows for beef to be consumed mostly raw, with just a sear of the outside, while chicken needs to be cooked thoroughly to eliminate lingering bacteria that have burrowed into the interior of the meat.

Image for post Once again, Brikk deserves all recognition for these super-cute dancing, smiling sushi.