Have the laws of Kashrut changed?

The halakha does not change, but it seems that the invention of soap changed reality. All the foundations of hilchot keilim remain in place, and only in laws that actually depend on absorption of flavor, has the law changed.


Rabbi Eliezer Melamed

Judaism הגעלת כלים בירושלים
הגעלת כלים בירושלים
פלאש 90

The Basis of the Mitzvah of Kashering Utensils

Three years ago, I shared with the readers the explanation of an important and complex halakhic issue that arose in the past generation, and now I will briefly summarize it with its main halakhic conclusions.

After Israel defeated Midian and captured their spoils, they were commanded to kasher the vessels as they were used – “k’bolo kach polto” (in the same manner a utensil absorbs, it also releases what it has absorbed). In other words, utensils used for cooking – their kashering is done by hagalah (immersing in boiling water), and utensils used for roasting or baking – by way of libun (kashering with direct fire until the vessels becomes red-hot), as the Torah says: ” This is the rule that God commanded Moses: As far as the gold, silver, copper, iron, tin and lead are concerned, whatever was used over fire must be brought over fire and purged… that which was not used over fire need only be immersed in a mikveh” (Numbers 31: 21-23).

At the basis of the mitzvah, our Sages explained that the taste of a food cooked in a utensil is absorbed in its walls, and if after cooking a treif (non-kosher) food in a pot, kosher food is cooked, the treif flavor is released from the walls and is absorbed in the kosher food. And our Sages instructed that since we do not know how much taste is absorbed and stuck to the walls, and what strength it has, the walls must be considered as if they are filled of the prohibition. Since the pot contents are almost always not sixty times the thickness of the walls, it follows that whenever a dish is cooked in a pot that has absorbed a forbidden taste, everything that is cooked in the pot will be prohibited. The same applies to a pot in which milk was cooked and then meat, that since in the meat dish there is not sixty times the thickness of the walls that absorbed milk, the meat dish is forbidden. In order to be able to cook in a treif pot, it must be kashered as it is used – “k’bolo kach polto” (Avodah Zarah 74b; 76b).

The halakha goes according to Rabbi Shimon, that if the treif pot had not been used for twenty-four hours, be’di’avad (after the fact), the dish cooked in it is not forbidden, because after a period of twenty-four hours the taste absorbed in the utensil is pagum (defective), and a taam pagum (defective taste) does not make the dish forbidden. But l’chatchila (ideally), it is forbidden to use the utensil without kashering it (S. A., Y. D. 122:2).

The Big Question Nowadays

In recent generations it has become clear beyond any doubt, according to the experience of many people who have examined it in their home kitchen, as well as scientific research, that metal vessels, similar to glassware, do not absorb flavors and consequently, also do not emit them. In other words, if milk is cooked in a pot, and afterwards the pot is thoroughly cleaned, and then meat is cooked in it, the meat will not have any taste of milk. And if treif meat was cooked and then the pot was cleaned well, and immediately afterwards a vegetable dish was cooked in it, the vegetables will not have any taste from the treif meat.

Ostensibly, since the obligation to kasher a utensil is to remove the flavors that have been absorbed in it, after it has become apparent that metal and glass utensils do not absorb flavors – the Torah’s commandment to kasher them after treif has been cooked in them, is null and void. On the other hand, however, we have learned explicitly in the Torah that it is a mitzvah to kasher metal utensils?

Have Metals Changed?

At first, I speculated: perhaps metals have changed and in the past they were less solid and impervious and therefore absorbed flavors, similar to earthenware and wood utensils. However, it turns out that metals of various types are common substances known not to have changed, and unlike clay and wood that have pores through which taste-bearing materials can penetrate into the thickness of the utensil, flavors cannot penetrate metal-bearing materials because the taste molecules are far larger than the spaces between the particles from which metals are made.

If so, the question remains: How is it possible that our Sages said that metal utensils emit flavors from the previous dish cooked in them, but today we do not taste it at all?

The Change Comes From the Invention of Soap

After further study, I discovered that the change that has taken place in recent generations is in our ability to clean utensils. Only a little over two hundred years ago (1790), Nicolas Leblanc, a French chemist, discovered the method used to make detergent, the basic substance of soap, which can dissolve and remove fats and grime. In a gradual process, the use of soap became common, until about 100 years ago, liquid soap, which in time was used worldwide, also began to be produced in Germany.

In other words, in the past, although utensils were washed well, and materials such as ash and burr which work similar to soap were used, almost always particles of food cooked in utensils remained stuck to their sides. These tastes were called “absorbed flavors”, since they became one with the sides, and secondary to them. In addition, metal surfaces are covered with tiny holes (which can be seen with a microscope) and taste-bearing materials can enter them, and may be considered as actually absorbed in the metal, even though they do not penetrate into its thickness. In earlier times, metal utensils were often coarser, and the holes in their walls were larger.

Nevertheless, as long as soap was not used, even after serious cleaning, there was almost always a thin layer of residue food leftover on the side of the utensil which transferred tastes. And because the liquids in this layer evaporated, the taste-bearing materials remained there in a high concentration, to the point where our Sages hypothesized according to experience that sometimes their taste was equal to that of the thickness of the walls. And since it is a thin layer exposed to air, an accelerated biochemical processes of decay would have occurred, to the point where our Sages hypothesized that if the utensil was not ben yomo (over 24 hours had passed), it was already clear that the taste that stuck to, and absorbed in its walls, were pagum.

Evidence from the Poskim

After understanding this, with the help of Rabbi Maor Cayam shlita, I found that in essence, this is what emerges from the words of the Rishonim, who explicitly wrote that at the time utensils undergo hagalah, the filth and grime emitted from the utensils into the water becomes very thick. Thus, they were speaking about the fats that were stuck to the sides of the utensils which the boiling water had melted until they mixed-in with the water. Consequently, Rabbi Aharon Halevi (Ra’ah) wrote that many utensils should not be immersed in the same water, for fear that “there will be a lot of zohama (filth), and consequently, the power of the water (to extract the tastes) is nullified, and the water changes its form…” (Bedik HaBayit 4: 4); and thus wrote Ran, that many utensils should not undergo hagalah “to the point where the water changes its form due to emitted material from the utensils, for it is as if one immersed a utensil in sauce…” (Chulin 44a, in dapaei Rif), and as explained by many other Rishonim.

Today, the water does not change form because utensils are cleaned with soap.

The Obligation to Kasher Remains

In light of this, the obligation to kasher metal utensils used with treifre mains in place, since even in the past, metals did not actually absorb tastes within them; thus, the obligation to kasher them is because when they were used with treif, the tastes stuck to their sides. And just as it is obligatory to kasher treif utensils after twenty-four hours have passed, even though the taste-bearing material stuck to them is already considered pagum and not prohibited, similarly, it is also obligatory to kasher utensils after removing all the remnants of food with soap.

If we delve into the words of the Rishonim, we find they differed whether the obligation to kasher after cleansing, similar to the obligation to kasher a treif utensil after 24 hours passed, is from the Torah or of rabbinical ordinance. According to those poskim who believe that “ta’am k’ikar d’Rabanan” (‘a taste is like the entity itself’ is of rabbinical ordinance) (Ramban, Rambam, Ra’ah, Ran, Nimukei Yosef, Ritva, and others), since the tastes that were absorbed and stuck to the utensils are not prohibited by the Torah, thus, the obligation to kasher utensils from the Torah also applies to tastes that became pagum or were removed, or as Ramban wrote that the kashering of utensils is for “a virtuous reason,” similar to the mitzvah of immersing utensils that a Jew bought or received from a non-Jew in a mikveh(Ra’ah, Bedek HaBayit 4: 1). And in the opinion of those poskim who believe that “ta’am k’ikar D’oreita” (‘a taste is like the entity itself’ is from the Torah)” (Bahag, Tosafot, Rabbeinu Tam, Terumah, Ra’zah, Raavad, Rosh, and others), after the taste is removed or is pagum, the obligation to kasher is of Rabbinical ordinance.

The Halakha in Laws Dependent on Taste

According to this explanation, all the fundamentals of the laws of kashering utensils remain in place, and only in laws that actually depend on taste, has the law changed. For example, if one made a mistake and cooked kosher food in a treif pot, just as if 24 hours had passed since the treif was cooked in the pot the food cooked in it is kosher, similarly, if the pot was cleaned with soap, even though 24 hours had not passed since the treif was cooked – the food cooked in it is kosher.

However, if it was done be’zadon (maliciously), in other words, one knew that the pot required kashering, and nevertheless he cooked kosher food in it, from Divrei Chachamim (Rabbinical ordinance), the food cooked is forbidden for anyone who it was cooked for, even though in practice, the pot did not emit forbidden tastes into the cooked food. There are, however, some later poskim who were lenient even for someone who cooked it be’zadon (Tiferet Le’Moshe, Maharam Shick, Iggrot Moshe, and others), but in practice, one should be machmir (act stringently), as many Rishonim and Acharonim wrote (among them, Rashba, Ritva, Radbaz, Knesset HaGedolah, Pri Migadim, Beit Shlomo, Zivchei Tzedek).

Cooking Parve Food in a Basari Utensil (Nat-Bar-Nat)

As well known, the Rishonim differed on the question of whether it is permitted to cook parve food in a basari (meat) pot in order to eat it with chalav (dairy), or vice versa (this law in Hebrew is called “nat-bar-nat d’hetera“).

In accordance with the words of the Rishonim, three minhagim (customs) were established:

1) the minhag of some Sephardic Jews, who hold that l’chatchila (ideally), one is permitted to cook in a ben yomo basari pot (a pot that 24 hours have not passed since meat was cooked in it) a parve food in order to eat it with chalav.

2) The minhag of most Sephardi Jews is that, l’chatchila, one should not cook parve food in a basari pot to be eaten with chalav, but if the basari pot is not ben yomo, one can cook a parve dish in it, in order to eat it with chalav.

3) For the minhag of Ashkenazic Jews, even b’shaat ha’tzorech (time of need), parve food cooked in a basari pot that is ben yomo cannot be eaten with chalav, and only be’di’avad (after the fact), if it got mixed in, it may be eaten. And if the basari pot is not ben yomob’shaat ha’tzorech it may be eaten with chalav.

According to what we have learned, all this is intended for earthenware utensils that absorb flavors, or metal utensils that have not been thoroughly cleansed with soap. However, in a metal utensil that has been cleansed with soap, members of all ethnic groups can act according to the lenient method.

The Law Concerning Charif

Similarly, the Rishonim differed as to charif (sharp, or spicy) food. Some poskim are of the opinion that the spiciness of the food enhances taste, therefore, if one cooks or cuts a charif food in a basari pot, the cooked dish becomes basari, and the minhag is to take into consideration their opinion (S. A. 91: 1).

However today, when pots and pans are cleansed with soap, the lenient opinion should be followed, namely, if one cooked or cut a charif parve food in a clean basari utensil made of metal or glass – the food remains parve, and may be eaten with chalav, or vice versa.

This article appears in the ‘Besheva’ newspaper and was translated from Hebrew.