Kashering Glass

Question

I inherited glass dishes. I would like to use them. How do I kosher them?

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Answers

  1. The Just Ask! - AskTheRabbi.org Team

    Glass is complicated because it is hard to define it according to Halacha.

    According to one opinion, glass does not have to be kashered at all because its surface is so smooth that it cannot absorb any flavor. Another opinion maintains exactly the opposite: glass cannot be kashered at all because it is made of sand and is halachically considered earthenware. There is even another opinion that maintains that glass has the halachic status of metal and can be kashered.

    According to Rav Moshe Feinstein, Pyrex, Duralex and Corningware cannot be kashered because of the concern that it might be made of sand and therefore “unkasherable.” There is a minority opinion that does allow for the kashering of Pyrex and other heat-resistant glass utensils by the process of hagalah (immersion in boiling water) – see Shaarim Metzuyanim Behalacha Chapter 116:11 and Rav Ovadia Yosef, Yechave Daat, Volume 1, Chapter 7.

    Best wishes from the AskTheRabbi.org Team