Sushi: Why Such a Short Shelf Life?

Packaged sushi on sale at the supermarket commonly has a "sell-by" date of the following day or even the same day.  How long can you keep it?  It sometimes scares me by starting to turn brown by the day after purchase.  So I asked the scientists on our site's Advisory Board to discuss the hasty spoilage and possible dangers that might be associated with one of my favorite ethnic foods. 

Note: Food scientists make a distinction between "spoilage"-- greatly diminished quality (bad taste, odor, texture, etc.)-- and the presence of pathogens that could cause illness.  Either can be caused by bacteria.  Either can adversely affect sushi.

Are there health risks associated with common sushi ingredients such as raw fish, seaweed, and/ rice (this last being much under attack these days)? Our research has been reassuring. Still, there are precautions consumers should take when handling sushi. Let's find out what they are.

Definitions and Distinctions

Let's begin with clarifying information from Snopes.com: "Contrary to popular belief, sushi does not mean raw seafood.  Instead, the word refers to the vinegared rice that can (but may not always) be paired with raw seafood." Snopes goes on to explain that the raw fish is called "sashimi," and the pressed seaweed paper is called "nori." Sashimi can be combined with vinegared rice and, sometimes, nori to make one type of sushi.  However, sushi can also be made with cooked seafood, for example, crab, shrimp, or octopus. 

Snopes also defines maki and nigiri. "Maki" is rolled sushi; the ingredients are placed upon a sheet of nori.  The product is then rolled into a log, which is sliced into round pieces.  (Temaki, one type of maki, is similar but served in the shape of cone.)  "Nigiri "gives the diner only one main ingredient, which is placed upon a finger of rice.  When eating nigiri, the fish should be removed, dipped in soy sauce, and then replaced on the finger of rice. 

Accompanying sushi, there is always "wasabi," the green horseradish paste, and gari, thin slices of pickled ginger root. 

Sushi Shelf Life

In general, shelf life information is about quality, not safety.  However, when the food in question is sushi, the shelf life answer may concern both.  If the sushi contains sashimi (raw fish), the shelf life is shorter than sushi with cooked fish.  However, in both cases, sushi is best if eaten immediately after it's made. That's fine if you're ordering it in a restaurant, but you may be wondering how long you can keep the packaged sushi you pick up in the grocery store or the sushi you make at home. Here are some answers from experts, two members of the Shelf Life Advice Advisory Board and other reliable sources. 

Food process engineer Dr. Timothy Bowser: "I think the shelf-life of sushi is relatively short because of the nature of the food. The sushi (makimono or gunkan-maki sushi) that is wrapped in seaweed (nori) may have a very brief shelf-life because the nori can become moistened by the rice or other ingredients and lose its texture and flavor. I don’t think the cooked rice is dangerous in itself, because it should essentially be pasteurized during the cooking process. Vinegar is traditionally added to the rice used in sushi, increasing its shelf life and adding flavor. If the rice is mishandled or contaminated by another ingredient, it may become dangerous."

Food scientist Dr. Catherine Cutter: "Sushi made with a raw product should be eaten within a day or two."

The website Eat by Date:  This site recommends that sushi and sashimi made with raw fish be consumed within 24 hours of preparation.  It points out that the following types of sushi, not containing raw ingredients, can be held for a day or two beyond preparation: California roll (made with cooked crab meat), Philadelphia roll (made with smoked salmon), and tempura shrimp roll (made with deep fried shrimp).

Health magazine: In a recent article entitled "Is that Sushi Safe?" the magazine responds with a qualified "Yes." The magazine says that, generally, refrigerated raw fish is considered safe for 3 days.  However, the article also recommends not eating sushi past the sell-by date--which usually gives you 1 whole day!  The article also says that sushi made with cooked fish and/or vegetables can be consumed up to a week after preparation if it's been in a refrigerator set at 40° or below.  Well, it may be safe to eat a week later, but the quality could be disgusting.  If it smells bad, discard it.

Sushi Storage

Eat By Date website:  If you're not going to serve the sushi immediately after preparing it, wrap it tightly in plastic, then place it in an airtight container, and refrigerate it promptly.

Dr. Cutter:  "Sushi does not freeze well."

Dangers: Raw Fish and Risky Rice

RAW FISH:

Remember, sashimi contains raw fish.  The FDA recommends that people with reduced immunity-- due to cancer, AIDS, or other diseases--avoid eating sashimi. 

It's also recommended that pregnant women avoid raw fish. In an article advising expectant mothers about their diets, the FDA says the following: "Foods made with raw fish are more likely to contain parasites or bacteria than foods made from cooked fish. Don't eat raw or undercooked finfish or shellfish (including oysters, clams, and mussels)."  

Since sushi makers in restaurants deal with raw fish, Dr. Cutter raises this question about sanitation: "I wonder how the restaurants clean those bamboo mats the sushi is usually prepared on."

Health magazine quotes Dr. O. Peter Snyder, president of the food-safety consulting group Hospitality Institute of Technology and Management.  He says that (aside from a rare outbreak from sushi containing scrape tuna) raw fish hasn't caused problems with E. coli and salmonella as have occurred in burgers and chicken.  He says that sushi is more likely to become unappetizing from spoilage than to become contaminated with dangerous pathogens.  (Fortunately, spoilage often causes us to throw out food before dangerous pathogens can take hold.)

According to the FDA, the process of heating raw fish sufficiently to kill bacterial pathogens is also sufficient to kill parasites. However, if you're preparing and serving sushi with raw fish, you want to be sure that it was frozen long enough and at a cold enough temperature to kill parasites such as nematodes and tapeworms, which are a health hazard. 

The FDA recommendation is for  freezing and storing at -4°F (-20°C) or below for 7 days (total time), or freezing at -31°F (-35°C) or below until solid and storing at -31°F (-35°C) or below for 15 hours, or freezing at -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for 24 hours.

The FDA's Food Code recommends freezing conditions listed above to retailers who provide fish intended for raw consumption.  Home freezers are usually kept at 0°F, so you want fish that has been kept in an industrial freezer (which should be -15°F or lower) for  one of the specified times listed above. This is commonly referred to as "sushi-grade fish."

These conditions will kill parasites but not necessarily bacteria, Dr. Bowser points out.  For more information about parasites in fish, click here.

RISKY RICE:

Rice can also be a health risk, whether it's in sushi, mixed with other food, or served by itself as a side dish.  Recently, there has been much public concern about the amount of arsenic in rice.  For more information on this topic, click here.  The matter is still being investigated by the FDA. Meanwhile, don't binge on rice.  Don't eat rice cereal for breakfast, chicken rice soup for lunch, marshmallow rice treats for a mid-afternoon snack, and sushi for dinner.  It's easy to consume a lot of rice in different forms without even noticing it.  Instead, the FDA suggests, vary your diet and eat many types of grains.

Another possible problem with rice: white rice frequently contains inactive bacteria called Bacillus cereus.  These may form protective spores that survive the high temperatures of cooking.  If rice is heated slowly or cooled slowly, these spores may grow and produce a toxin that causes vomiting.  Reheating rice will not inactivate the toxin, nor will it kill all the bacterial cells.  Therefore, it's important to heat rice quickly, keep cooked rice hot, and, if you have leftovers, cool these quickly.  If you handle rice properly, you need not fear bacterial contamination.  Rice can be cooled quickly by placing the container into a larger container of ice water for a few minutes before refrigerating it.  ABC Health and Wellbeing recommends discarding uneaten rice after it's been in the fridge for 3 days.

Yes, you can enjoy sushi and still protect yourself from food-borne illness.  But keep in mind that this delicacy is fragile.

For information about the shelf life of various types of rice, click here: http://shelflifeadvice.com/grains-pasta-and-cereal/grains-and-pasta/rice

At the left margin, you'll find links to many Q/As about rice. 

Source(s):

Timothy J. Bowser, Ph.D., Oklahoma State University, Dept. of Biosystems and Agricultural Engineering

Catherine N. Cutter, Ph.D., Pennsylvania State University, Dept. of Food Science

Health "Is That Sushi Safe?"  September 2012.

eatbydate "How Long Does Sushi Last? How Long Does Sashimi Last?"

http://www.eatbydate.com/proteins/seafood/how-long-does-sushi-last-shelf-life-expiration-date/

straightdope.com "Is homemade sushi dangerous?"

http://www.straightdope.com/columns/read/1580/is-homemade-sushi-dangerous

ShelfLifeAdvice.com "What Put Salmonella in the Sushi?  Mystery Solved"

http://shelflifeadvice.com/content/what-put-salmonella-sushi-mystery-solved

Snopes.com "If You Knew Sushi"

http://www.snopes.com/food/ingredient/sushi.asp

abc.net.au   "ABC Health and Wellbeing "Will cooked rice give you food poisoning if not stored in the fridge?"

http://www.abc.net.au/health/talkinghealth/factbuster/stories/2009/01/27/2475255.htm - .UI1UUrRQ0yE