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Koshering Utensils – Part II


Last week’s article discussed kitchen utensils that are impossible to kosher, mainly those classified as klei cheres – earthenware vessels. This week we will focus on glassware. Why do some see them as earthenware with regard to hilchos Pesach (and impossible to kosher), while transferring from meat to dairy without koshering during the year? Seemingly, Sfaradi and Ashkenazi halachic discourse has led to different conclusions. How should an Ashkenazi behave when invited to a meal in a Sfaradi household? What is the reason for the difference in halacha? How can glassware be koshered for Ashkenazi adherents, and when is koshering permissible? Can an empty whiskey bottle be used to store Pesach wine? Is there any difference in halacha if the glassware was certainly used for chometz, or if it was only possibly used for chometz? Is there any difference between drinking glasses and tea cups? What can be done if it is impossible to find kosher l’Pesach or new drinking glasses? Of this and more, in the coming article.


Last week, we discussed earthenware vessels which the Gemara describes as impossible to kosher. The reason for this is based on two factors: immersing earthenware in boiling water is impossible because it doesn’t release that which it absorbed; and although torching or firing it causes a release of the absorbed flavors, this aggressive treatment may ruin the vessel. Therefore, Chazal forbade employing it out of concern koshering would not be done properly.

This week we will focus on another natural substance used for cooking and serving – glass. Next week’s article will discuss contemporary materials and their pertinent halachos.

Glassware in the eyes of the Rishonim

The Rishonim are disputed regarding koshering glassware. Rabbenu Yechiel opines that koshering glassware is impossible for two reasons: glass is made of molten sand that turns to liquid at incredibly high temperatures. Since it is made of sand — a form of earth — it is considered earthenware. Secondly, even if glass is different from earthenware, nevertheless, since it may be damaged by boiling water, the second reason to forbid koshering earthenware is applicable – we are concerned it will not be koshered properly out of concern for the dish. (Heat resistant glassware will be discussed further on.)

In the past, glassware was not heat resistant and was only used for cold foods. If it was used for chometz it was only for cold food or drink. Therefore, koshering did not required immersion in boiling water. However, Rabbenu Yechiel wrote that since people sometimes soak hot bread in wine for a long time, the flavor of the bread is absorbed in the glass (liquid that sits in a vessel for 24 hours leaves a cooked-in flavor in the vessel. And a sharp drink leaves its flavor in even less time.)

The Ra’avia, though, disagrees (464) maintaining that glassware does not require immersion in boiling water for koshering because glass is a strong material that does not absorb flavor at all. Therefore, even if chometz was cooked in it, or if a meaty utensil was mistakenly used for dairy, the utensil be used immediately without koshering.

The Ra’avia proves his opinion from two sources: 1) The Gemara (Psachim 74b) teaches that the heart is an organ that does not absorb blood because it is smooth. Glass, being also a smooth substance, also does not absorb flavors. 2) Avos D’Rabbi Natan (41:1) lists the virtues of glass, one of which is that it doesn’t absorb or release flavor (as opposed to earthenware).

The following authorities agree with Rabbenu Yechiel’s approach: Hagahos Maimonios (CM 5:25), the Mordechai (Psachim 247:574), Trumos Hadeshen (I 132), The Agur (736), and Rabbenu Peretz. In their opinion, even smooth glass absorbs flavor. However, the Rashba (I:233), Rosh (Psachim 2:8), Ran (Psachim 9a), and Rabbenu Yerucham (54, II, 40a) all follow the Ra’avia’s ruling that koshering glassware is unnecessary.

Glassware in the Achronim

The Shulchan Aruch (OC 541:26) follows the lenient opinion of the Ra’avia. Therefore, according to the Shulchan Aruch even if hot bread was soaked in wine in a glass goblet, the goblet may be used for the Seder without koshering. The Rama’s ruling, however, follows Rabbenu Yechiel’s reasoning that sees glass as absorbent and similar to earthenware, making it impossible to kosher.

Despite his leniency with regard to glass, the Shulchan Aruch points out that if the vessel is glass covered ceramic or earthenware (CorningWare or Cuisinart, for example), koshering is impossible.

This creates an unbridgeable gap between Ashkenazi and Sfaradi halachic ruling. While glassware is impossible to kosher for Ashkenazi adherents, for Sfaradi followers they require no koshering at all. According to Sfaradim the same glass cup can be used for boiling coffee with milk and boiling chicken soup (separately, of course). The same is true for Pesach – a glass cup used for hot oatmeal (before Pesach) can then be used at the Seder for soup without koshering. For Ashkenazim this is impossible, obligating them to purchase separate glassware for Pesach.

While some Sfaradi authorities are stringent like the Ashkenazi opinions (Ohr Letzion III, 10:12), most follow the Shulchan Aruch’s opinion.

As a result, the Mishna Brura rules (451:154) that a drinking glass used mostly for cold drinks, but sometimes also for hot drinks cannot, l’chatchila, be koshered for Pesach. However, he adds (footnote 194), post facto, once the dish has already been used, if it was mostly used for cold chometz, food placed on it on Pesach does not become prohibited. Similarly, a glass that is usually used for coffee, which while hot, only contains non-chometz ingredients (even if occasionally used for hot cereals or chometz soup), if it was used on Pesach for a hot beverage, the drink it not prohibited.


Hot Pesach food that was placed on chometz glass cookware (oven-to-table or dishes used in a microwave) is prohibited for Ashkenazim. However, where this will cause a significant loss (because the food was exceptionally expensive or necessary for the Yom Tov meal) if 24 hours have passed from the use with chometz, according to the Mishna Brura one can be lenient.

Glass Container

The Mishna Brura writes (451:155) that a container used to store cold chometz for over 24 hours (such as a whiskey bottle) absorbs the flavor of the chometz even if never used for hot foods. If it was used for storing liquid on Pesach for more than 24 hours or with hot foods, the food or drink is forbidden even b’dieved.

If the container was only used to store chometz but not to cook it, where stringency would involve a significant loss (e.g. the bottle was used to store kosher l’Pesach Tequila Ley) the Mishna Brura writes (451, Sha’ar Hatziyun, footnote 197) that one can be lenient.

Chometz Dishes

The above is true for dishes that were used for various foods, some of which are kosher l’Pesach (such as wine or soup), and some which are not. However, a vessel used exclusively for chometz (e.g., beer kegs) are seen by the Chayei Adam more severely – yeast dregs and residue remain on the keg, making koshering impossible. Therefore, these vessels cannot be used for Pesach even in extenuating circumstances.

Aruch Hashulchan (451:49-50) explains why we are more stringent with containers that stored chometz beverages: bottles retain the smell of the beverage stored in them even after thorough cleaning. This kind of vessel requires koshering for Sfaradi followers, and is impossible to kosher according to the Rama. The Ohr Letzion (volume III, chapter 10:12) also follows the Ashkenazi approach.

Rabbi Moshe Feinstein (Igros Moshe OC I, chapter 151) explains that bottles used for storing chometz cannot be koshered because cleaning them is very difficult. Therefore, despite looking clean, Chazal determined them impossible to kosher. Vessels, however, that were used for both drinks and foods, some of which were chometz and others which were not, may be koshered in the method that will be described below even if chometz remained in the vessel for over 24 hours. This, adds Rav Moshe Feinstein, also depends upon the accepted practice in the given locale – while in Russia people did not customarily kosher these vessels, in the US they did.

Possible Chometz

If the ingredients used in the container are unknown to have been necessarily chometz (e.g., a glass teacup where people don’t generally dip cookies in their tea) despite them not being necessarily kosher for Pesach, the container may be koshered.

No Other Glasses

Where there are no other glasses, the Mishna Brura writes (451:156) that cups used with hot chometz can be made kosher for Pesach through immersion in boiling water. Cups that were not usually used with hot chometz can be koshered by filling with water for 3 days, changing the water every 24 hours.

If visiting in a Sfaradi household and there is no other glass for a hot drink on Pesach, an Ashkenazi can submerge a glass cup that was not used for hot chometz in boiling water and then use the cup immediately. The same is true for people in a hospital or wherever one has no access to disposable dishes.

The Mishna Brura writes that where one can buy new glasses for Pesach, Ashkenazi adherents should not kosher old glasses at all, but rather purchase a new set for Pesach.

Koshering Glass

Where it is necessary to kosher glass dishes: if the dish can withstand boiling water, it should be dipped in boiling water. If it cannot withstand high temperatures, it should be immersed in cold water for 3 days, changing the water every 24 hours. The 3 days don’t necessarily have to be consecutive.

Bottle Neck

The Mishna Brura notes (451:156) that according to all opinions, since cleaning a bottle with a neck too narrow for a hand to enter is impossible, it cannot be used on Pesach. Today, with modern bottle cleaners this assertion requires further review. However, stained bottles or dishes (such as glass oven-to-tableware) cannot be koshered for Pesach even if the stains are impossible to remove.

Meat and Diary

All contemporary poskim agree that according to the Ashkenazi poskim glassware cannot be transferred from meat to dairy and vice versa. A household should have separate glassware for meat and for dairy (Simlat Chaim 12; Minchas Yitzchok 9:75; Shevet Halevi III chapter 42; Tshuvos V’hanhagos I chapter 432). Some opinions are lenient for meat and dairy but not for Pesach (Sridei Esh, I 45). Sfaradi poskim rule that glass does not absorb taste. Therefore, separate glasses for meat and dairy are unnecessary.

The Minchas Yitzchok (I, chapter 86) is of the opinion that glass can be made kosher during the year but not for Pesach.

Therefore, when an Askenazi is offered a cup of coffee in a Sfaradi household in a glass which has also been used for hot chicken soup, he should refrain from drinking it. However, if the glass is not usually used for hot meaty foods, only occasionally: if 24 hours have passed from the last meaty use and the coffee has already been poured, one may be lenient.

When a Sfaradi host wishes to serve hot dairy drinks to an Ashkenazi guest, he should preferably do so in a disposable cup, or in a glass that was clearly not used for meat. This can be learned from Beis Hillel and Beis Shamai: while they normally did not refrain from marrying into each other, where one of the parties was a product of a tzoras erva levirate marriage, which is a great mitzva according to Beis Shamai and a prohibition according to Beis Hillel, they would inform each other that the union was, according to their counterpart’s opinion, forbidden.

Next week’s article will deal with heat resistant glassware, and other materials – porcelain, plastic, horn, and others.

Wishing all our readers a chag kosher ve’someach!


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