The Kashrus Of Pickled Herring

Have you ever noticed that when herring is served at a kiddush or during shalosh seudos, not only does the herring not have fins or scales, it often doesn’t even have its telltale skin? What identifies the herring as kosher fish? The answer is, of course, that originally there was a skin on the herring, and fins and scales were there too. The story of how herring sheds its scales, and other kashrus events in the life of processed herring, are a bit unusual. It begins far off the coasts, deep in the night…

Our story begins far off the coasts, deep in the night. That’s when fishing for herring is done because that is when herring rise to the surface of the ocean to feed on rising phytoplankton, and they are therefore most accessible to the fishermen’s net. Using sophisticated sonar equipment, fishermen can locate herring even in the pitch black. After they  have located the herring, fishermen can catch an entire school in one fall swoop using a traditional fishing method called “purse-seining.” A seine is a rectangular net with a sinker, or weighted bottom, on one long end of the net, and buoyant cork on the parallel end. The net is dropped vertically, and then drawn around the school like a curtain. A large boat holds one end of the net. A smaller boat, called a skiff, pulls the free end, wrapping the whole school of fish (see Figures). Next, a string at the bottom is pulled to lock in the catch, much like drawing the strings of an old-fashioned purse – and hence the name: purse-seining. While the net is slowly pulled onto the larger vessel, the fish are forced together towards the bottom. At this point the fish are either pumped onto the fishing boat directly from the net, or are removed by “brailing” – pulled out with small hand-held dip nets called brails.

Amazingly, most of the scales fall off the herring as they are being removed from the water. Most remaining scales are removed by fishermen using a process called vacuum harvesting. Even these shed scales have some economic value: fishermen sell them to cosmetic companies who grind them and use them in make-up!

By the time these fish are brought to the processing plant, they have almost no remaining scales. If a representative from the kosher certifying agency is not right there on the boat with the fishermen (which is not likely) how does the kosher certifying agency know that the fish are kosher? After all, the Torah requires that one identify kosher fish by their snapir v’kaskeses, fins and scales, and those scales are no longer present?

One answer can be found in comments from the Darchei Teshuva (Yorah Deah 83:1) who notes that, although scales may no longer be present on a fish, someone familiar with a kosher fish based on its skin can still identify that fish as kosher (a concept known as tevias ayin). This line of reasoning is accepted by the preponderance of kashrus agencies that certify herring. Other suggestions are also offered by Poskim for finding scales on a fish that apparently no longer possesses them. One can carefully check behind the gills, behind the fins (especially the dorsal fin), or by the tail, where one will likely find a remaining scale. Another suggestion is to wrap the fish in a cloth and check for scales in the cloth (Remah, Yorah Deah 83:1). These methods for identifying a fish are only applicable while the skin is still present. .

When the herring catch is brought to the processing facility, plant personnel remove any by-catch, which is the term used by the industry for species that were incidentally caught in the fishing process. Among the different species that can be found as by-catch are small sharks, and therefore it is the responsibility of the kashrus agency to monitor that one hundred percent of the non-kosher by-catch is removed.

Once sorted, the herring will be “dressed”, which has nothing to do with tznius! Dressing means the herring will have its head, viscera (guts), and tail removed. Often this process is done by machine, although some producers, especially smaller ones, still dress fish manually. If the dressing is done manually, the kashrus supervising agency must confirm that the workers do not take the knives used to dress the fish outside of the processing area. This is because of a concern that the workers might use their knives to cut, say, a delicious shark sandwich for lunch.

Much of the herring served these days is skinned herring. The processing facility removes the skins of the fish at this point, after the herring have been dressed.

Since kashrus agencies rely on the presence of the skin to identify herring as herring (following the Darchei Teshuva cited earlier) the fact that the skins are removed forces kashrus agencies to contend with the question of a skinless herring. In the language of chazal, skinless fish are called kirvei dagim (literally the inner part of fish). Kirvei dagim are assur d’rabonon (rabbinically prohibited) because of a chashash d’oraysoh (potential Torah prohibition) that the fish being represented as kosher is actually a dag tamay (non-kosher fish). Once the skin of the herring has been removed, how can one know that the fish is in fact a kosher herring?

Some agencies will simply require on-site supervision (hashgocho temidis) from the time the skin is removed. They would require the on-site supervisor to place a seal, or siman, on the containers holding semi-processed fish before he leaves the facility. He would also need to be present whenever the herring is being processed, until the product is bottled. Other agencies recognize the distinctive silver-blue flesh layer underneath the herring’s skin as being a siman muvhak (literally an absolute sign of identity). This opinion maintains that since no other fish shares this distinctive quality, merely having the silver-blue flesh layer is enough to guarantee the kosher status of the fish. Yet another opinion is to evaluate the nature of a manufacturing plant’s business. If the plant manufactures kosher fish exclusively, and has no financial benefit in trying to substitute a non-kosher fish for herring, an agency would certify all products made in the facility as kosher. The halachic justification for this opinion is based on the shas klal of u’man lo mareh umnaso (a professional does not wish to damage his reputation). These agencies require a mashgiach to be yotzei v’nichnas to confirm that the plant continues to produce kosher fish exclusively.

Additional concerns arise later in the processing, and will be treated in next week’s edition.

Part 2

Last week’s Kashrus Kaleidoscope dealt with the supervision of herring preparation until the herring is cut and skinned. The next step in processing of herring is called curing. Curing is, in layman’s language, the pickling stage. Salt, glacial acetic acid (a petroleum-based ingredient) and vinegar are used to preserve the herring (the saltiness of the salt and acidity of the glacial acetic acid or vinegar creates an environment hostile to bacteria, which are responsible for decay of foods). Besides preserving the herring, these ingredients help the herring taste better.

Although glacial acetic acid and salt are free of kashrus concerns, vinegar can be derived from non-kosher wine, and therefore it is necessary that a hashgacha has secured a kosher source of vinegar. Because most herring facilities receive vinegar in bulk shipments (in tanker trailers, for example), the kashrus agency must set up a protocol at the plant to guarantee that only properly certified and approved vinegar is received.

Herring is generally cured in barrels, and after the curing the process the barrels are sealed. For those agencies that require hashgacha temidis on the preliminary stages of the herring preparation process – the dressing, skinning, and curing steps – the rabbi who oversaw those steps would put a distinctive seal, or some other form of siman kashrus, on the barrels. When the barrels are opened, a rabbi must therefore be present to open the barrel as well and confirm that the seal is intact.

After the containers are opened, the herring is dumped into steel tanks where it is washed from the brine that it was pickled in. The washing process is called “desalting”. The tanks into which the herring is dumped must be used exclusively for kosher fish or has been koshered. The reason is that herring, before it is desalted, is a davar charif and therefore can rapidly pull out the bliyos of a container it is placed in. While normally bliyos are not transferred through “kvisha” in under 24 hours, dvarim charifim pull out bliyos in only minutes.

After the herring is washed, plant personnel will mix various brines, sauces, and spices into the herring before bottling. Herring in wine sauce is a fixture in the product line of herring companies, and the wine used in the wine sauce is the most sensitive of the ingredients used in this stage. Incidentally, the amount of wine used in herring in wine sauce is invariably minute. Usually, wine sauce really consists mostly of adding more of the petroleum-based glacial acetic acid that was also used in the original curing stage. Some herring companies use the same 750milliliter bottle of wine for months! Nevertheless, because non-kosher wine can easily be purchased, a hashgacha agency must see to it that only kosher wine is used.

Onions are used in most herring products. The people that cut the onions may be inclined to remove the knives from the production floor and use them for some other purpose. A system must obviously be in place to make sure that these knives are used exclusively under hashgacha. An additional kashrus consideration regarding peeled onions will B’EH be discussed in a future article

The tasty, well-preserved herring is finally ready to be pumped into the glass jars that we see in the market. The machine that pumps the herring into the jars is called a bottling machine, and it fills the jars with herring and brine to the absolute top of the jar. These filled-to-the-top jars move along a conveyor belt to a capping machine. The capping machine is a steel box with a conveyor belt running through it. A constant jet of steam shoots through the steel box. The force of the steam displaces a small amount of product brine before the machine applies caps to the jars.

The steam that is captured inside the jar cools rapidly and condenses to water. Steam occupies more space than water, and so the condensation of the steam to water has the effect of collapsing the space between the herring and the cap. That collapse pulls a safety button on the cap down and creates a vacuum seal.

Occasionally, the capper machine is splattered by the herring sauce that was displaced by the steam injection. Before a kosher herring run, or a pareve herring run after a dairy run (herring in cream sauce), it is critical that the capper be cleaned. There is a potential for non-kosher or dairy zeyah from the splattered residue to make its way into a kosher or pareve product. Some capping machines use a belt, instead of steam, to wipe off excess product from the top of each jar before capping. The belt must be confirmed to be clean between dairy to pareve or from non-kosher to kosher production runs.

One final step in the process must be considered. Herring is sealed in clear glass jars. These glass jars can contain non-kosher product. A kashrus agency must set up systems to guarantee that a label bearing its kashrus symbol is used for certified product only. If there is any concern about mislabeling in a facility, an on-site mashgiach will control the usage of the label until the kosher production is over. He will collect any unused labels and remove them from the facility or leave them at the facility only when secured under a special seal.

So, while you’re enjoying the wine sauce, cream sauce, or just the traditional herring in onions, remember to appreciate the complexities that herring presents and the measures taken to guarantee that it is kosher.

Halachic Insights/Fish FAQs

Q: How do we identify a kosher fish?
A: The Torah 1 says that the simanim of kosher fish are “snapir v’ kaskeses”. However the Gemara 2 tells us that all fish that have “kaskeses” have “snapir”, so in practice, all one needs to determine that a fish is kosher is that it has kaskeses!

Q: So what exactly is kaskeses?
A: “Kaskeses” is generally translated as scales. Nonetheless, not all scales are considered kaskeses. This is because the Ramban, in his commentary on the Torah 3 tells us “kaskesesare scales that can be easily removed by hand or with a knife without tearing the skin. Scales that are embedded in a fish (or are not visible to the naked eye 4) are not “kaskeses”. The Ramban’s definition is universally accepted, and in fact the Rema 5 rules that those scales that cannot be easily removed (according to the parameters that will be discussed below) cannot be called “kaskeses”.

Q: I heard there a several different scientific classifications of scales. Which are kaskeses?
A: Though scientists categorize scales by certain characteristics, the Torah is only concerned with whether or not a scale can be easily removed without tearing the skin, irrespective of its shape, color or size6. From the Torah’s perspective, the various scientific classifications of scales are irrelevant.

Q: What are some examples of fish with scales that are not kosher?
A: Sturgeon definitely has scales7 , but it is not kosher. Its scales are classified as “ganoid”, which means that they are covered with ganoin (similar in texture to fingernails) and cannot be removed without tearing the skin. Burbot has cycloid scales (one of the types often referred to as “always kosher” ) yet because they are embedded, this fish is not kosher. Sand lances may have tiny scales, but since they are not visible, this fish is not kosher.

Q: How can I know if a fish is kosher?
A: To check if a fish is kosher, one must ascertain that its scales could be properly removed8. Scales are attached on the side to the fish on that side of the scale which is closer to the head and are not attached on the other side of the scale which is closer to the tail. To remove the scales, one must grasp that side that is not attached and gently pluck it off from the side of the fish9. If removing the scale did not damage the skin, then the fish is kosher.

Q: My local fish store is not under Rabbinic supervision, and it sells fillets without skin. How could I tell if the fish they are selling are kosher?
A: You cannot! Even if the fish is halibut, whitefish or carp (all kosher fish), once the skin is removed it is impossible to identify, and it cannot be assumed to be kosher. In determining the kosher status of fish, identifying the species is critical.

There are two ways to identify a kosher fish:
1) By removing a kosher scale from the skin.10
2) By recognizing the fish as being from a kosher species. One can only recognize a fish species if the skin is still intact. It is generally impossible, even for a “maven”, to identify fish without skin. The exception to this rule is that the Orthodox Union accepts salmon and red trout fillets without skin, as there is no non-kosher fish whose flesh resembles that of a salmon or red trout.

For example, let us say that you want to purchase tilapia.11 You heard that tilapia is a kosher fish, and the friendly counterperson assures you this scale-less fillet is tilapia. You simply cannot rely on this person, unless he is both observant in Torah and mitzvos and is familiar with the laws of kosher fish. Now let us say that a tilapia-eating friend (who is halachically reliable) comes to the store with you and recognizes a fish in the display case whose scales have been removed (but the skin is still intact) as tilapia. Even though its scales are not present, you may eat this fish because a halachicly reliable person has positively identified it as kosher. Therefore, one can only purchase skinless fillets from a store under reliable Rabbinic supervision.

Q: What if only a patch of the skin is left on a fillet?
A: If you can have someone (halachically reliable) confirm the identity of a fish based on a patch of skin, this would be sufficient.

Q: Why is it so difficult to publish an accurate kosher fish list?
A: The reason is that “common names” are a highly inaccurate way of describing a fish. For example, there are several fish known as “red snapper”. Who can say for certain that every fish called “red snapper” is in fact kosher, when “red snapper” could be referring to so many different fish? Another instance that we have found common names to be misleading is in the case of “Escolar”. Escolar could refer to Ruvettus pretiosus (kosher) or Gempylus serpens (non-kosher). Yet another is “Ling” which could refer to 6 different species of fish most of which are in fact kosher. However when the OU examined a sample of one of these “Ling” fish whose Latin name is Lota Lota (also called Burbot, Freshwater Cod, Eelpout, Lawyer and other names) we found it to be not kosher.

Latin names are more accurate. It would be possible to create a list of kosher fish by Latin name. The problem is that fish sellers never refer to fish by Latin names, and have generally no knowledge of the correct Latin name for a fish! In one case, we asked a kosher fish store the Latin name of a certain (kosher) fish and the Latin name provided was that of a completely different, non-kosher fish!!!

Though your mother was right, and you should not judge a book by its cover, you should most certainly judge a kosher fish by its cover… its scales and identifying skin!

The Halachic Insights was reprinted from a longer article published in The Daf HaKashrus, the OU’s newsletter for Mashgichim.


1 Vayikra 11:9.

2 Chullin 66b.

3 Vayikra 11:9.

4 Aruch HaShulchan 83:15.

5 Yoreh Deah 83:1

6 Rabbi Y. Ephrati wrote this in the name of Rabbi Y. Elyashiv in a Teshuva dated the 11th of Elul, 5763).

7 More precisely scutes, which are technically defined as “enlarged scales often containing one or more bony projections.” See Peterson’s Field Guides Freshwater Fishes, 1991, Drs. Lawrence Paige and Brooks Burr.

8 Teshuvos She’vas Tzion #29 cited by Pischei Teshuva 83:1, states that it is necessary to actually remove the scales and not merely rely on the rov (i.e. majority) that most scales are easily removed.

9 I have not found this procedure explicitly, though this is simply the way to check the kosher status of a fish. Though the Nodah B’yehudah permitted a fish similar to sturgeon whose scales became removable only by soaking it in an alkaline solution, the Pischei Teshuva rules like the Teshuvos She’vas Tzion (cited above) who does not allow it.

10 The consumer need not personally remove the scale. The consumer only needs to see the scale removed and that the skin did not rip from having the scale removed. He must additionally be sure that the scale being removed was in fact attached to the fish before removal (and not that it was actually a scale from another fish which merely was stuck to this fish.)

11 The U.S. Food and Drug Administration (the “FDA” ) officially lists 7 different tilapia that are marketed in the U.S, though there may be more. It is not possible for the Orthodox Union to ascertain that all species of tilapia are kosher.