Which Materials May Be Kashered (and Which May Not)

Kashrus Kurrents Summer 2012

Q: I have a number of utensils which need kashering through hagalah (immersion in boiling water). Which materials may and may not be kashered?

A:   A fleishig utensil which comes into contact with hot milchig food or a milchig utensil which comes into contact with hot fleishig food needs to be kashered before further use.  There are a number of methods for kashering, dependent upon the manner of contact between the utensil and the food.  Perhaps the most common form of kashering is hagalah, in which the utensil is immersed in boiling water.

The Torah tells us that a vessel may be kashered if it is made from one of six metals:  gold, silver, copper, iron, tin or lead.1  There are other metals and alloys which were not in common use at the time of Matan Torah that are currently used to make kitchenware, such as aluminum and steel.  The Poskim state that these materials may be considered comparable to the six metals that the Torah mentions, and may be kashered.2

Earthenware and Ceramic
The Torah tells us that an earthenware vessel may not be kashered.3  The Torah is referring to a vessel which has been fired in a kiln.  Most Poskim allow the kashering of a vessel made from earth which has been dried in the sun,4 although some Poskim disagree and are stringent.5  Ceramic is equivalent to fired earthenware and may not be kashered.6  Corningware is a ceramic material and also may not be kashered.7

China and Porcelain China
China and porcelain china8 should be considered similar to earthenware, and should not be kashered.9

Stone and Granite
Stone or granite slabs may be kashered.10  However, granite countertops are often made from granite composite, which consists of crushed granite that is glued together.  Rav Heinemann, shlit”a, paskens thatgranite composite may not be kashered.11

Wood and Leather
Wood may be kashered through hagalah,12 as long as it has no cracks or crevices.13 Leather may also be kashered through hagalah.14

The Shulchan Aruch paskens that glass is not an absorbent material and never needs kashering.  It is sufficient to merely wash the glass utensil and clean it.15  Regarding kashering for Pesach use, the Rema says that it is customary for Ashkenazim to treat glass similar to earthenware and not to kasher it.16  Many Poskim contend that the Rema was stringent only regarding Pesach use.  However, if a utensil needs kashering for non-Pesach use, we would accept the opinion of the Shulchan Aruch that glass is not absorbent, and agree that it is sufficient to merely wash the utensil.17 Some Poskim state that this is true only for glass cups and the like, which are not directly placed on a flame, but not for glass pans which are put on the flame.18  Rav Heinemann paskens that glass pans which are placed on the flame should not be kashered. 19

Pyrex and Corelle
Rav Moshe Feinstein, zt”l, told Rav Heinemann that Pyrex is equivalent to glass.20 Rav Heinemann paskens thatCorelle is also equivalent to glass.21 However, one should be aware that the Corelle company also produces stoneware dishes, which maymay not be kashered.22

Porcelain Enamel coating
The Chasam Sofer states that an enamel coated utensil may not be kashered through hagalah.23  The Mishna Berura paskens that it may not be kashered for Pesach use,24  but mentions that he heard that there is a custom to kasher enamel coated metal utensils for non-Pesach use, due to the fact that the coating is thin and insignificant.25  However, it is unclear whether the enamel coating which is currently used has the same properties as that which is mentioned in the Mishna Berura.  Therefore, Rav Heinemann paskens in accordance with the Chasam Sofer,that enamel coated utensils may not be kashered.26

Plastic and Teflon
The Poskim debate whether or not plastic may be kashered.27 Rav Heinemann asked Rav Moshe Feinstein, zt”l, who told him that it is unclear as to what extent plastic absorbs; therefore, it should not be kashered.28 (In situations where kashering is not definitely required it may be possible to rely on the opinion that plastic may be kashered; a Rav should be consulted).  Nevertheless, Rav Moshe Feinstein states that Teflon may be kashered.29 Presumably, this is because Teflon acts as a non-stick agent, and may be considered non-absorbent.

1. במדבר לא,כב-כג

2. עי’ שו”ת אג”מ או”ח ח”ג סי’ נח

3. ויקרא ו,כא   

4. מג”א סי’ תנא ס”ק ד הובא במ”ב שם ס”ק יח 

5. חזו”א יו”ד סי’ קכ ס”ק ב

6. ספר הגעלת כלים לר’ צבי כהן פי”ג ס”ק תטז  

7. http://www.corningware.com/index.asp?pageId=99  

8. http://www.madehow.com/Volume-1/Porcelain.html

9. מ”ב סי’ תכא ס”ק קסד ושו”ת אג”מ או”ח ח”ג סי’ נח ואהע”ז ח”ד סי’ ז ודלא כשו”ת שאילת יעב”ץ ח”א סי’ סז הובא בפת”ש סי’ קכ ס”ק ב, וע”ע בשו”ת אג”מ יו”ד ח”א סי’ מג וח”ב סי’ מו וח”ג סי’ כז   

10. שו”ע יו”ד סי’ קכא סעי’ ב 

11. שמעתי ממו”ר ר’ היינעמאן שליט”א, ועי’ בדרכי תשובה שם ס”ק כה   

12. שו”ע שם  

13. שו”ע או”ח סי’ תנא סעי’ ג    

14. ב”ח יו”ד ס’י קלה ס”ק כז ופמ”ג או”ח מש”ז סוף סי’ תנא  

15. שו”ע או”ח סי’ תכא סעי’ כו  

16. רמ”א שם, ועי’ במ”ב שם ס”ק קנה ובשעה”צ שם ס”ק קצו לענין בדיעבד 

17. חי’ רע”א על המג”א סי’ תכא ס”ק מט בשם המנחת יעקב כלל פה ס”ק יב, הובא בשו”ת מהרש”ם ח”ג סי’ צד ושו”ת אג”מ או”ח ח”ה סי’ לב אות א  

18. שו”ת טוב טעם ודעת תליתאי ח”ב סי’ כה

19. שמעתי ממו”ר ר’ היינעמאן שליט”א 

20. שמעתי ממו”ר ר’ היינעמאן שליט”א, ועי’ http://www.madehow.com/Volume-7/Pyrex.html  

21. שמעתי ממו”ר ר’ היינעמאן שליט”א, ועי’ http://www.corelle.com/index.asp?pageId=1   

22. עי’ http://www.corelle.com/index.asp?pageId=30  

23. שו”ת חת”ס יו”ד סי’ קיג הובא בפת”ש סי’ קכא ס”ק ב 

24. הגהת המ”ב סי’ תכא סעי’ כג בשולי העמוד   

25. עי’ בהגהת המ”ב שם    

26. שמעתי ממו”ר ר’ היינעמאן שליט”א 

27. עי’ בספר שבות יצחק ח”א עמ’ נג בשם הגרי”ש אלישיב שליט”א ובשו”ת מנחת יצחק ח”ג סי’ סז ובשו”ת ציץ אליעזר ח”ד סי’ ו ובשו”ת חלקת יעקב יו”ד סי’ מה ובהל’ פסח להגר”ש איידער פי”ג הערה י’ בשם בעל האג”מ    

28. שמעתי ממו”ר ר’ היינעמאן שליט”א   

29. שו”ת אג”מ אהע”ז ח”ד סו”ס ז