Is there a scientific explanation for the concept of "blias issur" absorption of taste in pots. Like for example if since heat expands materials maybe the taste creeps in.

(I'm not asking about whether today pots and pans absorb, rather I am asking if the concept has a scientific explanation)


3 Answers 3


Repost from Dave

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.”

  • 7
    ...and then the engineer converted to Judaism and his descendants taught Torah in Benei Berak?
    – Double AA
    Jun 24, 2015 at 19:51
  • 1
    I would like some authoritative sources quoted, scientific or halachic. this is just, as @doubleAA touches on, is just a nice fluffy story that makes you feel warm inside Jun 24, 2015 at 20:00
  • whats wrong with a little fluff?
    – user9478
    Jun 24, 2015 at 20:01
  • @mokay fluff or not, it's not sourced authoritatively which is what I'm looking for. Jun 24, 2015 at 20:10
  • 1
    I'm not sure I'd call it "fluffy": I'd call it too neat to be credible.
    – TRiG
    Jun 25, 2015 at 1:19

As far as I know (from experience around the industry) this is a generally recognized phenomena. Consider Flavor Scalping, where the packaging absorbs the flavor of the contents and vis-versa. Now, I'm sure in the details the Halacha is way more strict in many cases beyond a scientific understanding of the situation, but the basic notion is certainly well known in the food industry.

Yes, food engineers generally don't think stainless steel absorbs, but stainless steel is a modern invention not discussed in Chazal. Other materials have different characteristics.

Wood barrels are used in some alcohol making specifically because they want the flavor transfer into the food product. The transfer isn't only one-way, and that itself can be reused to make other alcohol after the absorption has occurred.

All of the above more speaks to Kavush - leaving materials at rest over a long period of time. But part of the effect is kinetic (as described in the source of the first link), and the rate of diffusion increases under heat.

All of the above is for polymers, primarily, but the idea that this diffusion happens with some other materials is recognized in the industry, as far as I understand.

  • My problem is not so much your answer being that empirical evidence can qualify as a scientific proof to some people. But I think it's ridiculous that Chazzal and Rishonim and achronim all discussed this phenomenon and its reality is questioned until some random guy on the internet named Yishai (whom we all love) says that he has experienced this, and now it is accepted as truth. Oy lanu.
    – user6591
    Jun 25, 2015 at 13:43
  • @user6591, I have no idea what you are trying to say?
    – Yishai
    Jun 25, 2015 at 13:49
  • Really? I don't think I could restate it any clearer, sorry. This is not a tayna on you, it's a tayna on people who think this is an answer. Think Gal Shel Atzamos.
    – user6591
    Jun 25, 2015 at 14:15
  • 1
    Oaked Sherry => Sherry cask whiskey => Whiskey Oaked beer. All we need is Beer Barrel sherry to complete the Circle of Alcohol... Jun 25, 2015 at 14:29
  • @user6591, you totally lost me ...
    – Yishai
    Jun 25, 2015 at 14:45

Surprisingly enough, proteins (such as those found in food, especially in meet) have a great affinity in binding to steel surface layer. On top of this, proteins also tend to affect the chemical composition of the stainless steel surface, by selectively releasing metal ions from the stainless steel alloy.


The following article delves into some details regarding the effect of albumin (a protein commonly found in milk and blood) on stainless steel vessels:


  • 1
    Adsorption would not explain why we need to measure the entire volume of pot walls and its bottom when deciding if there is sixty or not.
    – user6591
    Jun 25, 2015 at 2:04
  • 1
    @user6591, that is not going to be explained scientifically (nor do I think it really needs to be - it is an estimation technique, the original idea was to have someone taste the food).
    – Yishai
    Jun 25, 2015 at 2:45
  • @Yishai what I meant is that we are obviously dealing with absorption in these halachos which is starkly contrasted to adsorption in that first link. Adsorbtion only has to to with surface level. Nothing deeper than that.
    – user6591
    Jun 25, 2015 at 13:02
  • 1
    @Yishai There are any number of halachos which would prove we are not dealing with merely surface level taste. The drip of milk that hits the pot and goes through either to the rotev or by the empty part is another one that comes to mind.
    – user6591
    Jun 25, 2015 at 13:40
  • @user6591, yes, that is true. My point is just that scientifically taste is caused by the same molecules as the substance. When you read this in Halacha you can get the misimpression that taste is an ephemeral quality that can take up the same space as the actual pot. That isn't going to be the scientific view, and I doubt it is the correct understanding of the Halacha as well.
    – Yishai
    Jun 25, 2015 at 13:51

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .