Just so you know: Canned sardines are kosher.

This judgment would appear to be definitive, based on DNA evidence. Genetic testing by a parasitologist at the American Museum of Natural History has confirmed that the recent discovery of small worms in canned sardines does not render them treyf, or unkosher. It may render them unappetizing, but that judgment is up to the consumer (more on that later).

The museum got involved last March when rabbis from the Orthodox Union, which certifies as kosher hundreds of thousands of products across the world, sought scientific help in resolving a question that arose when they began finding the worms, or nematodes, in cans of sardines.

Talmudic debates can turn on fine distinctions, but this was relatively straightforward. The presence of worms could have been a sign that, during the preparation of the canned sardines, muscle from the fish had been improperly handled and allowed to mix with intestinal contents of the sardines, rendering them unkosher.

The issue was important because it “could have led to sardines losing certification as kosher,” said Dr. Mark Siddall, a curator and professor in the invertebrate department of the museum, who conducted the testing. Many consumers, including non-Jews, look for the certification label as a sign of quality assurance in food preparation.

The rabbis brought their samples of sardina pilchardus — the Mediterranean sardine — to the museum, where Dr. Siddall conducted so-called “DNA bar-coding” to analyze the species of the worms. Their DNA was isolated and two variants of the cytochrome oxidase gene — which is different for every animal species, as unique as a fingerprint, Dr. Siddall said — revealed that the type of worms in the samples reside only in the flesh of sardines. “This meant that there was no evidence that the intestines and the flesh had been commingled,” Dr. Siddall said.

The Orthodox Union also discovered evidence of worms in cans of orange capelin roe, and Dr. Siddall’s testing confirmed that the worms, as well, were not intestine-dwellers. The analysis of Dr. Siddall and his colleagues has been published in The Journal of Parasitology, and the union has formally ruled that both the sardines, and the capelin roe, are kosher. (The entire paper can be read below.)

In 2004, a similar Talmudic tempest involved a tiny crustacean known as a copepod, which was discovered swimming in New York City’s tap water, spurring debate among the observant about whether it rendered city water unkosher. Many contended that the crustacean was a distant relative of shrimp and lobster, shellfish that cannot be consumed because they lack fins and scales. The Orthodox Union recommended that city water be filtered before using it for drinking and cooking. That prompted restaurants to install filters, some costing more than $1,000, to remove the interlopers.

As for worms in sardines or in any fish, Article 81 of the New York City Department of Health Code has long required that “aquatic animals, fish or molluscan shellfish” be cooked, rendering such parasites harmless — unless customers assume some risk by asking for raw fish, as in sushi. The best sushi masters constantly examine the fish for evidence of parasites.

“The notion that there are worms in fish flesh is not new,” Dr. Siddall said. “As long as they’re cooked, or frozen first, they’re perfectly safe.”

Yes, but if the sardines are both safe and kosher, are the worms themselves — which are barely visible and look like thin whitish threads — disgusting?
“It is up to the individual’s aesthetic as to whether that is ‘yucky,’ ” Dr. Siddall said. “I’ve eaten worse. Curdled goose blood. Rhino beetle larvae. Both yummy. But that’s another story.”

Journal of Parasitology paper

Read more:
DNA Results Are In: Canned Sardines Are Kosher