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The Influence of Science on Kashrut

In a recent issue of Ha-Ma’ayan, Rabbi Dr. Israel Meir Levinger wrote an article (Hebrew) about scientific findings relating to the absorption and expunging by vessels. This is potentially very important for issues of Kashrut. In the most recent issue there were a number of responses. The original article and the responses raise a number of important issues that deserve serious discussion. HT to Rav Tzair for linking to the articles.

7 Responses to “The Influence of Science on Kashrut”

  1. 1

    As one of the respondents shows, there is no reason to believe that any metal or glass vessels absorb anything. The experiments essentially measured what was stuck on the surface of the different materials and which could have been removed (and was in some of the experiments) by simple washing.

  2. 2

    Sounds intressante. Can you possibly sumarize?

  3. 3
    Menachem Mendel (Michael P.):


    On one foot Levinger presents the results of a study that attempted to measure the absorption and expelling by different materials. It’s not surprising that some materials absorbed very little or nothing (glass), while others were the opposite. The responses to his article: 1. Halakhic and scientific definitions are different; 2. The article doesn’t give enough information about amounts in order to get a clear picture; 3. A more in-depth series of experiments is currently being done.

  4. 4

    Thank you, MM.

    Ultimately, of course, as you know, science will have no impact whatsoever on the halacha. We can be happy about that, or we can tear our hair out, but there you go.

  5. 5

    DF — Not entirely true as new things come up and poskim decide, theoretically including a thorough review of the science. One famous example where a decision was made “based on the science” — but, it turns out based on bogus science — is Pyrex.

  6. 6

    “It’s not surprising that some materials absorbed very little or nothing (glass), while others were the opposite.”

    Not quite. What’s not surprising is that fats (and other substances) tend to stick to the outer surface of some materials (metal) more so than others (glass). But as one of the respondents makes clear, that is as much as one can conclude from the study, since they didn’t actually clear surfaces properly before measuring “absorption”. It would be very surprising if any metal absorbed any measurable quantity of anything.

  7. 7

    “Not entirely true as new things come up and poskim decide . . .”

    Yes. I agree. I was speaking in broad terms. To be more specific, I was speaking of older issues – such as the overall question of beliah – in which nothing will ever change, no matter how much reality has changed. See Techeles, tzitzis; See Aleppo Codex, nusach. Etc. Etc.




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