Glass Dishes for Meat & Dairy
Jonathan Katz at MIT wrote:
What is the Halacha regarding the use of the same set of glass dishes for both meat and milk (not at the same time of course)?
The main factors to consider in answering this question are:
- Is glass "absorbent" in the Halachic sense of the word?
- If it is "absorbent," then can that which was absorbed into it be completely expunged?
Thus, we have three practical possibilities:
It is not It won't absorb the Can be used for both absorbent flavor of either milk and meat. the meat or the milk. It is Absorbed flavors Should not be used for absorbent can be removed by both meat and milk. kashering. However, a "mistake" can be rectified by kashering. It is Absorbed flavors Can not be used for absorbent cannot be removed both meat and milk. by kashering. Also, cannot even be kashered if a "mistake" was made.
Glass is made from sand, and would therefore seem to be in the same Halachic category as earthenware (which is super-absorbent and cannot be kashered). On the other hand, the resultant glass vessel is hard and smooth - unlike earthenware - which would indicate that it is non-absorbent, and would therefore never need to be kashered.
Glass is a difficult material to classify Halachically, because it shares its origin with one class of material, but has physical characteristics that differ from items of that class.
Because of these unusual characteristics, there are a few different opinions in Jewish Law concerning glass dishes:
- Rav Yosef Karo rules that you can use glass for both milk and meat, and just rinse them off in between.
- Rav Moshe Isserlish writes that glass is like earthenware, and it is therefore forbidden to use the same dishes for both meat and milk.
- There is a third opinion that holds that glass is absorbent, but that it can be kashered through the process of "hagala" (immersion in boiling water).
I spoke to Rav Chaim Pinchas Scheinberg, shlita, about the Halacha in this case. He told me that Sephardic Jews rule according to Rav Yosef Karo, and therefore use glass dishes for both meat and milk, while Ashkenazic Jews conduct themselves according to the opinion of Rav Moshe Isserlish, therefore refraining from the use of glass dishes for both. But, he said, because there are different opinions regarding the Halacha, there is room for leniency in cases where extenuating circumstances exist (for instance, a Ba'al Teshuvah who is going for a family visit where the kitchen is not kosher, but glass utensils are used). Should such a situation arise, you should contact your LOR for advice.
While we are on this topic, there are many types of glassware that are specially treated in order to make them more break-resistant and heat-resistant; i.e., Pyrex, Duralex, Corelle, Corningware, and the like. I asked Rav Scheinberg if there is any difference between these and regular glass dishes with regard to the issues discussed above. He told me that all of these types of treated glassware share the same Halacha as that which applies to regular glassware.
- Shulchan Aruch, Orach Chaim, 451:26.
- Ohr Zeruah 2:256.