Throughout all of Yoreh Deah Chelek Alef and Hilchos Pesach (and perhaps other places in Shulchan Aruch as well) we see the idea of "blias" ("absorptions") by celim. That is to say there is a "taste" that is left in a pot or pan after cooking in it. Therefore if someone would cook meat in a pot, then within the same day cook milk in it (even though there is no meat in the pot now), still there is a "taste" of meat that was left inside of the pot walls when it was first cooked. That taste will now come out of the pot when cooking milk in it and will prohibit the milk.

This is all true of a metal pot. However, a glass pot, according to the Machaber, doesn't take in any taste at all. On the other side of things, if one has a pot made of "cheres" (earthenware), he would never be able to expunge taste from it once it was cooked in (not like a metal pot which one could kasher by making ha'galeh on it).

I'm having a difficult time understanding how this din (rule) is still relevant to today's pots. Is there really a taste left inside of a metal pot? Once upon a time a metal pot that was cooked in over time would slowly become dirty, grimy, filthy, covered in black, clearly used. One could look at this and understand that there is a "taste" left in the walls of the pot. However, I don't see how this is true of a normal metal pot in today's market, which is smooth, finished off, and more or less retains it's original color and look and stays clean over time. Where is the "taste" in the walls of this pot? If someone would cook milk or meat in it and then cook water in it, would the water have any taste to it (assuming the pot was cleaned in between)? While I don't see any posek (halachic decisor) using this argument even as a "tziruf" (argument in combination with other leniencies) to be lenient in a question of issur v'heter (forbidden combinations), still, I'm looking for any poskim that perhaps spoke about this or entertained the possibility. Maybe today's "metal" pots are more like a glass pot, which the poskim say doesn't retain any taste of what's cooked in it.

  • Thank you to @msh210, who addressed my first concern. On my second concern, I still think pans might be different from pots (assuming you are correct). Frying definitely leaves behind something you can see over time, at least with metal pans; Teflon® might be different.
    – Seth J
    Commented Feb 14, 2013 at 15:04
  • Incidentally, Yehoshua, the Rema (and therefore, Ashkenazim) hold that glass is like חרס. Glass would certainly show a visible absorption, if what was visible was the concern. At least for the Rema, it would seem that visibility has nothing to do with it..
    – HodofHod
    Commented Feb 14, 2013 at 15:59
  • @HodofHod Some Achronim only apply that Rama for Pesach. Also, it seems from the wording of the Mordechai that he quotes that the issue is a gezera one, not real blios.
    – Double AA
    Commented Feb 14, 2013 at 17:16
  • @DoubleAA Where is the Mordechai? Where is this quoted? (doesn't seem to be the Rema in SA. Maybe the Darchei Moshe in Tur/Beis Yosef or is this somewhere else?
    – Yehoshua
    Commented Feb 16, 2013 at 22:18
  • @hod can you grab the link from chat
    – Double AA
    Commented Feb 17, 2013 at 17:51

3 Answers 3


From a Kosher Spirit interview with Rabbi Chaim Cohn:

KS: Can you share a unique experience that you had while working at the OK?

RCC: I once had an argument with a plant engineer concerning whether or not stainless steel can absorb or not. He maintained and brought extensive documentation to prove that stainless steel can’t absorb anything and therefore should not need kosherization. I told him, your proofs are impressive but the Rabbis decreed 2000 years ago that metal needs kosherization and I do not have the authority to go against them. We agreed to differ.

Approximately a year later, I was in the process of supervising the kosherization of a 1000 gallon reactor and after the workers had meticulously cleaned it we brought it to a boil. There was about a quarter of an inch of scum on the top of the pot. The engineer was passing by and I called him over to look at it. I said, “This was a completely clean pot.” I turned to the workers and asked, “Right?” The workers nodded their heads vigorously up and down. The engineer looked at it and said, “ I can’t argue with empirical evidence,” and walked away.

Six months later I got a call from the engineer. He said, “Rabbi Cohn, I now understand.” “Great,” I thought, and asked, “You now understand what?” He answered, “I understand why a stainless steel vessel will absorb.” I asked, “Why?” He answered, “You have to understand, when it leaves the factory it can’t absorb anything, however, when it is heated it expands and contracts and it will produce micro fissures. Your Rabbis were right, you can’t measure this and therefore have to assume the worst-case scenario that the entire volume has absorptions in it.”

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    But Maasim BeChol Yom that I clean a pot with soap and water and cook other food in it without the slightest fear it will affect the taste. If anything is absorbed it's next to nil.
    – Double AA
    Commented Feb 14, 2013 at 17:41
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    Blias by a metal pot is only a gezera?
    – Yehoshua
    Commented Feb 14, 2013 at 18:18
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    @DoubleAA - according to the story, the reason could indeed theoretically apply to your stainless steel chicken pot. Not that it will happen every time with every person and every pot, but the possibility does exist.
    – Dave
    Commented Feb 14, 2013 at 18:26
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    @Yehoshua - I would say more like a universal chashash. Just as when you use a treif pot 100 times, all of the food becomes treif even though the absorbed issur is not enough to affect that large combined volume, since the issur could have been released during any single act of cooking.
    – Dave
    Commented Feb 14, 2013 at 18:30
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    Eh. I respect your sourcing this, but I completely disagree with the metziut then. I heard orally in the name of R ShZ Aurbach that indeed there is no real reason to kasher certain keilim which are obviously clean, but we do it anyway because of a minhag avoseinu of equivalent level to minhag avoseinu of electricity on shabbat. I have also heard from different people that R H Schachter has joked a number of times about how all the rabbis should just get together and permit stainless steel as kosher. Even if there are blios in the pot, it seems they are so small to be halachikly negligible.
    – Double AA
    Commented Feb 14, 2013 at 18:53

Rabbi Dov Lior of Kiryat Arba made a ruling "in principle" saying that modern stainless steel cookware does not absorb flavor at a halachiclly significant level.

Apparently two Avrachim from the Torat HaChaim yeshiva tested the amount of absorption of stainless steel and found it to be one part in 170,000 of the volume of the fluid cooked in the pot. In response to this test Rav Lior wrote:

"זוהי בליעה מזערית ביותר, ולכן נראה בפשטות שכלי נירוסטה הוא ככלי זכוכית"

This is an extremely insignificant amount of absorption, and thus it seems plainly that stainless steel pots are like glass.

Further, a letter was later published in the Makor Rishon newspaper in which he says:

"בשעתו אמרתי שאם יתברר בוודאות שיש חומר כלשהו שאינו בולע, דינו יהיה ככלי זכוכית, שלדעת ה'שולחן ערוך' אינו בולע ולכן אינו טעון הגעלה לפסח ודי בשטיפה"

At the time I said that if it will become certain that there is any substance that does not absorb, his law will be like the law of glass, that according to the Shulchan Aruch does not absorb and thus does not require "hagala" for Pesach and it is sufficient to wash it.

Rav Lior concludes:

"אף לדעת הרמ"א, המחמיר בכלי זכוכית, הדברים אמורים דווקא בכלי זכוכית שתחילת יצירתם מחול ולכם דינם כחרס. אולם כלי נירוסטה, שאינם בולעים כמעט כלום ונעשו ממתכת ולא מחול, מותר לבשל בהם בשר, לנקות היטב ואחר כך לבשל חלב באותו היום, והן להפך".

Even according to the opinion of the Rama, who is stringent with glass utensils, saying that since they are initially made from sand their ruling is like earthenware. But stainless steel utensils, that don't hardly absorb anything and are made of metal not sand, it is permissible to cook in them meat, to clean well and after to cook milk the same day, and the reverse as well.

In his letter to the two avrechim he says:

"מכיוון שדין זה עלול להתפרש כדבר חדש, בקשתי היא שיסכימו איתי עוד שני פוסקים ויצטרפו להיתר זה"

Since this ruling might be interpreted as something new, I request that two other poskim will agree with me.

All this according to Rav Ratzon Arusi.

Here is a video in which Rav Bar Chaim from Machon Shilo discusses his support of Rav Lior's ruling and his belief that it would also apply to forbidden substances. He mentions the above reported by Rav Arusi and also discusses a conversation with a Rav Dr. Moshe Antelman a PhD chemist who worked in industrial chemical engineering who joked with him that the absorption was, "approximately three atoms". In seriousness he said it was clear to him that there is no halachiclly significant absorption.

Rav Bar Chaim goes on to point discuss the 1/60th rule and how there was a machloket whether or not it applied only to earthenware pots or if it also applied to metal pots. He brings Rambam הלכות מאכלות אסורות יז to support that this is only regarding earthenware and points out that Ra'avad agrees with Rambam in this case as does the Rashbah and the Ran and list the sources.

קדירה של חרס שנתבשל בה בשר נבילה, או בשר שקצים ורמשים--לא יבשל בה בשר שחוטה באותו היום. ואם בישל בה מין בשר, התבשיל אסור; בישל בה מין אחר, בנותן טעם. [ב] ולא אסרה תורה אלא קדירה בת יומה בלבד, הואיל ועדיין לא נפגם השומן שנבלע בקדירה; ומדברי סופרים, לא יבשל בה לעולם. לפיכך אין לוקחין כלי חרס ישנים מן הגויים שנשתמשו בהן בחמין, כגון קדירות וקערות, לעולם, ואפילו היו שוועין באבר; ואם לקח, ובישל בהן מיום שני והלאה--התבשיל מותר.

A pot of earthenware in which the meat of a nevilah ( non-kosher meat ) was cooked, or the meat of bugs or insects -- don't cook in it kosher meat on the same day. And if he cooked the same type of meat in it, the cooked dish is forbidden; if he cooked a different type of meat then it is according to if it improved the flavor. And the Torah only forbid a pot on the same day, because the fat that has been absorbed in the [ earthenware ] pot has not yet gone bad; and our Sages forbid cooking in this pot forever. Thus, we do not take old earthenware pots from gentiles who have cooked hot in them, such as pots and bowls, ever, and even if it was [ something I can't translate ]; and if one took, and cooked in it from the second day on -- the cooked food is permissible.

He points out that the majority of Rishonim agree with the statement from Avot that glass does not absorb and that he agrees with Rav Lior's statement that stainless steel is like glass and that regular cleaning with soap is sufficient, i.e. that hagalah is not required. He further points out that according to his opinion washing with soap causes any matter that might remain on the surface of the pot to become "pagum", no longer considered food.

A side note of interest is that according Rambam's method, in specific cases where transfer of flavor is the criteria used ( and it's not used in all cases ) then it only applies if there is a trusted gentile physically present to taste the food for you and tell you if flavor has been transferred. Otherwise, transfer of taste is not applicable and you go by the 1/60 rule ( or 1/100 or 1/200 depending on the particular substance involved ). Another thing to point out is that transfer of flavor doesn't apply if the flavor transferred is a unpleasant or bad flavor. For example if a mouse where to be found in a barrel of wine it wouldn't make if forbidden because it doesn't improve the flavor of the wine.

Here's a list of the properties of stainless steel on wikipedia.

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    "שוועין באבר" means "coated with lead". It refers to the earthenware kunya vessels mentioned in 'Avoda Zara 33b.
    – Fred
    Commented Feb 20, 2020 at 8:21

A kashrus inspector told me the following "Very little, if any, perceptible ta'am exists in modern equipment. For most production, even a minimal washing (not heat sensitive) is considered adequate. Equipment used for flavor and flavor chemical production will sometimes be steam cleaned for days to ensure no residue of the prior flavor. Also, only glass is considered to be 100% impenetrable, metal are considered to allow some penetration through them."

I heard in the name of an unnamed great rabbi that when Moshiach comes, he is going to make some big changes in halachos like this. The halacha assumes the entire volume of the pot's walls and base are full of absorbed taste and therefore the volume of food inside the pot can never have 60 times the volume of absorbed taste in the walls. That was never possible even with the oldest pots and even more unrealistic today but I have never heard of a posek using any of your observations to be lenient.

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    Which Hashgacha, so I can avoid it :) Commented Dec 11, 2013 at 18:00
  • @ShmuelBrin, what is the problem with the statement? (If it means "considered adequate" from a production perspective - a company won't care to do more if not for Kosher requirements).
    – Yishai
    Commented Dec 11, 2013 at 19:52
  • @Yishai I understood it to mean that the Hashgacha won't kasher equipment (as it doesn't absorb) Commented Dec 11, 2013 at 20:01
  • ShmuelBrin, I understood it like @Yishai.
    – David Wave
    Commented Dec 12, 2013 at 20:59
  • "but I have never heard of a posek using any of your observations to be lenient." That would not be a reason that the halakha isn't valid. We have brains and we are expected to use them according to haRambam to the best of our ability to determine the halakha in the event that the Bet Din HaGadol has not ruled on the matter.
    – J J
    Commented May 26, 2017 at 12:21

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