The saying, "All Halal is kosher, but not all kosher is Halal," is a truism one can witness being repeated over and over on social media. It usually comes from well-meaning individuals trying to highlight how "Jews and Muslims are not so different," and therefore, we should get along.
Wonderful sentiment, but it shouldn't come at the expense of truth. The actual reality is that:
"The vast majority of Kosher products are considered Halal, but Halal is never considered kosher."
Before you protest, "but I've seen products with kosher and halal labels on them!" I am not saying it's impossible for something, once it has been declared halal, to be kosher, or that once it's declared halal, it loses its kosher status.
What this means is that there is no situation where, lacking a kosher certification, a Jew who upholds the laws of Kashrut can replace a product requiring Kosher certification (henceforth hechsher) with something Halal instead.
Indeed, certain food items do not require a hechsher. It's entirely acceptable to buy them as such, so one could find himself in a situation where a product is kosher without a hechsher but does feature a halal stamp. However, the halal symbol is entirely irrelevant as to whether the food is considered kosher. It would be with or without its halal status.
Kosher labeling (and the laws of Kashrut) carry weight in Sharia and are especially important for Muslims in countries where Halal food is hard to procure, but the reverse is not true. Sharia and Islamic dietary laws are not considered in any way whatsoever when it comes to Kashrut.
When Kosher is Halal
All solid food items that Halacha permits are permitted under Sharia. All liquid food items that Halacha permits (bar one) are permitted under Sharia.
Regarding all non-animal (or non-animal-derived) and non-alcoholic products, everything kosher is de facto considered halal for Muslims.
There are only two areas where Sharia conflicts with Halacha: Animal meat/byproducts and alcohol. And only alcohol is the one that is outright forbidden for Muslims, the other highly dependent on circumstances.
Still, even though they are permitted for Muslims, certainly the more observant Muslims will often tell you that between the choice of a product certified Halal and one only certified Kosher, you should go with the former even if it is cheaper or of lesser quality.
When Kosher is not Halal
The only universal prohibition of kosher products agreed upon by all Islamic schools of jurisprudence is kosher alcohol. It's not simply a question of kosher wine; any kosher foodstuff that includes a significant amount of alcohol would be forbidden for Muslims to consume.
A significant quantity would be defined as something that could either be detected by taste or lead to intoxication.
When Kosher is questionably Halal
The central object of contention regarding the permissibility of Kosher products for Muslims is meat. The issue lies in the Islamic concept of tasmiya. Tasmiya is the recital of Allah's name at the time of the slaughtering.
For the minority school that does not require any tasmiya before a Muslim slaughters an animal, it obviously would not require it from a non-Muslim either, and as such kosher meat (where the name of G-d is pronounced before the shochet slaughters it) would be entirely permitted.
The argument here lies between those who say that a tasmiya declaration must be made before every animal is slaughtered, in contrast to those who do not require it before every animal but once every few animals are permissible.
Jewish law is extremely stringent on regarding saying G-d's name without purpose. This is why in a case of a safek beracha (where it's unclear whether a beracha is required), we do not say/repeat it versus taking the risk of saying G-d's name in vain. When we do multiple mitzvot requiring a beracha, we usually recite a single beracha that will cover all of them. For example, before one puts on all of the mezuzot in his house, he will recite a beracha on the first mezuzah that he installs, bearing in mind that it will cover all the other mezuzot. As long as there is no significant interruption between the actions, he does not have to repeat it. The same applies to a shochet who will slaughter multiple animals.
This is very Islam and Judaism wildly diverge, and it becomes problematic for those requiring tasmiya for every animal. Those who permit one tasmiya for many, on the other hand, will qualify kosher meat as permitted as a result, while those who don't, won't.
This Sharia ruling will also have ramifications for kosher products that contain animal derivatives, such as gelatin or enzymes. Those who require individual tasmiya will abstain, while those who don't will be allowed to use kosher animal-derived byproducts.
However, even those who are stringent in this regard would still permit kosher meat if there's a sure way to ascertain that the shochet made a beracha before he slaughtered the animal.
Why Halal is not kosher:
Halacha is far more stringent than Sharia, something Muslims themselves admit (and the reason why they rely on Kashrut). Some domains where this is easily noticeable:
What's permitted versus what's forbidden.
Kosher versus halal slaughter rules.
Utensils, cooking, packaging, supervising, etc.
This is ultimately why halal can never be considered kosher; it does not fulfill any of the Halachic requirements in the first place. Not that Muslims would be offended by the idea. In fact, according to the Quran, they consider that it was a punishment for Jews not following Islam:
"For the wrongdoing of the Jews, We made unlawful for them certain good foods which had been lawful for them." [an-Nisa 4:160].
There is only one area where Sharia is more "stringent" than Halacha: the consumption of alcohol. As mentioned earlier, no kosher product containing a significant amount of alcohol is permitted for Muslims while, for Jews, well… lechaim!
Sharia permits far more than Halacha does.
The vast majority of Sharia jurisprudence schools permit the consumption of the nerves, fats, and body parts forbidden under Halacha. Jews are not allowed to eat kidney fat, tail fat, digestive system fat or abdominal fat, the sciatic nerve, the cheek, maw, or foreleg reserved for the Kohanim, etc. Only the Maliki school bans some* of them; otherwise they are wholly permitted for Muslims. They also allow some animals, such as camels, zebras, or rabbits, that Halacha forbids.
Sharia is divided on sea animals. Shia Islam believes all fish with scales and certain crustaceans like shrimp are permitted. Non-Hanafi Sunni Muslims can eat a wide variety of seafood, such as sharks, shellfish, crustaceans, etc. This means that prawns, oysters, shrimps, lobster, crab, catfish, swordfish, monkfish, cusk, blowfish, eel, and hagfish are considered halal by the majority of Islamic schools of thought. The Hanafi school permits only "fish" and includes species heel and hagfish. Halacha, in contrast, only allows for fish with both scales and fins, for starters.
Many types of birds are permitted under Sharia while they are forbidden under Halacha, such as ostriches, emus, peacocks, parrots, pigeons, swallows, sparrows, nightingales, or weaver birds; in essence, any bird without talons and a canine tooth.
Meat and milk, a very severe prohibition under Halacha, is non-existent under Sharia.
All milk from Halal animals is considered halal, which makes all kosher milk halal but not vice-versa. Regarding cheese, Muslims are far more lenient, and only minority opinions would forbid cheese made from non-Halal rennet, while in Judaism, cheese made from non-kosher rennet is prohibited.
Fruits and vegetables would be another area of difference, where Halacha is extremely stringent that no bugs be eaten, and as such specific types of vegetables (or parts of them) are de facto forbidden for Jews as they cannot be koshered adequately. There is no equivalent in Sharia. While they forbid bugs, it is not to the extent that Halacha requires.
*I have not found a list to ascertain precisely how close they are to Kashrut.
Shechita vs. Halal Slaughter.
Both Halacha and Sharia have a common set of requirements:
The animal needs to be alive before being slaughtered (therefore, stunning is not allowed)
The animal needs to be killed with a sharp knife (blow to the head, nail gun, electric shocks, etc. are not allowed)
The blade has to cut the neck arteries but not so deep it would sever the spinal cord
The blood must be drained
The animal cannot suffer unnecessary pain
However, there are major differences as well:
Slaughterer: Sharia allows for anyone of any age to slaughter, and not only Muslims but Xians and Jews too. As far as Halacha goes, only a Jewish man above the age of bar mitsvah and who has been explicitly trained to do the job is allowed after an extensive apprenticeship under a professional shochet.
The knife: Halacha requires a perfectly sharp and perfectly smooth blade. If there is any nick or imperfection whatsoever, the knife is not permitted to be used for shechita, and an animal slaughtered with it is considered treif. The blade also needs to be perfectly straight; depending on the animal, the length of the blade also matters. In Sharia, if the knife is sharp, it's entirely satisfactory if there are some nicks or abrasions as long as it does its intended job. A curved or straight blade is irrelevant, as well as its length.
The slaughtering itself: Halacha requires the animal to be shechted in one smooth motion without stopping for even a moment as the trachea, esophagus, jugular arteries, and carotid arteries are severed. Anything other than this, the animal is considered treif. As far as Sharia goes, multiple strokes wouldn't render the animal Haram as long as they are done in quick succession. Some Sharia schools require less than Kashrut regarding what needs to be severed, though the more stringent ones do require the esophagus, trachea, arteries, and jugular to be severed.
Stunning: Halacha says that a stunned animal would be considered treif if slaughtered in that state, while Sharia would say that it's a problem but still wouldn't it consider it haram if it was killed like this after the fact.
Spinal cord: if the spinal cord is severed during the shechita, the animal is now considered treif. While it optimally shouldn't be cut off as far as shariah goes, it still doesn't render the animal as haram according to some/most authorities.
Inspection: Halacha requires internal organs to be inspected after the slaughter, and if specific defects are found, the animal is considered treif. Even minor imperfections would be enough to make the meat merely kosher instead of the higher standard of glatt kosher. Other types, even negligible, would render the meat entirely non-kosher. There is no such concept in Islam.
Blood: According to Halacha, the animal's blood has to flow onto the earth (or the ground) after the slaughter. Once the animal is butchered, the salting process, melicha, must take place to ensure that all of the blood is out. This is crucial in the case of specific organs like the heart or the liver, which also require extra steps. Sharia cares neither about where the blood flows nor about salting the blood still extent in the meat or veins after death, aside from the blood that comes out of the animal's throat after it has been cut.
Without question, there is simply no situation where halal meat would ever be considered kosher.
Utensils, cooking, packaging, etc.
Muslims are not particular regarding how food is prepared, the utensils, or what goes on in the factory; the ingredients are what truly matter. A quick demonstration:
Say someone eats a cheeseburger with pig bacon on a ceramic plate.
The Muslim cleans it and can use it again immediately. The Jew throws it away because it's impossible to kosher it.
What about the metal forks and knives?
The Muslim cleans them and can use them again immediately The Jew would have to wash them thoroughly, wait 24 hours, then immerse them in a pot filled with rolling boiling water. Only then would they become acceptable again.
For Jews, there is the question of Bishul Akum vs. Bishul Yisrael as far as what a non-Jew would be permitted to cook or heat and it would keep its kosher status, versus what would become forbidden, something that does not exist by Sharia. A non-Muslim could cook kosher meat in a pot used an hour before cooking pork (as long as it had been thoroughly cleaned), and it would be perfectly halal. A non-Jew cooking halal meat in a non-kosher pot would break Halacha in at least three different ways.
To receive kosher certification, a qualified supervisor (Mashgiach) must be present to inspect the entire process. It is not so with halal food.
There are multiple concepts or parts of the Kashrut process that do not exist in Sharia, including but not limited to the following:
Chalav Akum vs. Chalav Yisrael Pat Akum vs. Pat Yisrael Agricultural laws (Kilayim, Chadash, Orlah, Shmittah, Maaser, and Terumah) Rules related to wine & grape juice Immersion of new utensils Kashering of utensils Meat vs. Dairy vs. Parve Bitul
I am not going to go into further details, but I think it should be crystal clear now why Halal food simply is not kosher.
Non-Jewish Vegan Restaurants
Now that we've dealt with the dietary requirements of one religion, let's turn to another: veganism. Shouldn't it be, logically, permitted to eat in a vegan restaurant even though it does not have a hechsher?
While, at first glance, it would seem to be the only non-Jewish place a Jew could eat without encountering problems, far from it. Amongst the issues to take into account:
Non-kosher appliances and utensils
Bishul Akum
Agricultural Laws
Bugs
Wine & grape juice/products
It is ubiquitous, especially for newly launched restaurants, to buy their equipment second-hand from other restaurants that declared bankruptcy or closed for one reason or another. There's, in fact, an entire market for it. It is quite possible that those appliances or utensils now in the vegan restaurant were previously used for non-kosher products and, thus, would need to be koshered. Even if they had not been used for treif food, once they are used in a situation of bishul akum, the pots and utensils would become treif, and so would the food cooked in them. It's also possible that grape juice or wine is used as a part of the recipe even if they are not offered on the menu, which constitutes a grave Biblical prohibition.
Only raw, uncooked vegetables? How do you know that some of the produce is not from Israel and, if it is, does not violate the prohibitions mentioned earlier? Even in a nigh-miraculous situation where none of the problems I've listed so far have been encountered, there is the question of bugs. It is impossible that a non-Jewish vegan restaurant would follow the guidelines of Kashrut as far as how to make sure no bugs are present. While it sounds like it should be easy, it is a very time-consuming and complicated process.
In conclusion, though some things might seem intuitively true, it’s necessary to take a closer look. It’s often going to lead to the realization that things are far from what they might seem.
Lechaim!