Kashering Dishes

Get your water boiling.

Print this page Print this page

However, because glass is neutral, the question has been raised: Could the same dishes be used for dairy and for meat, just washing them in between uses? While technically this is a possibility, both Conservative and Orthodox rules frown upon this as a practice. It is too easy for incidents of basar b'halav [meat and dairy mixing] to happen. Keeping track of when you used the dish last, if you washed it appropriately, and so on make it problematic to use the same glass dishes for hot dairy and meat foods.

Drinking glasses, however, since they are used only for cold substances, may be used with both dairy and meat meals. A mahmir [strict] Orthodox stand is to have separate drinking glasses for dairy and meat, but using one set of drinking glasses is not only acceptable but common practice.

Glass that is used for baking, such as Pyrex, is a separate issue. The Conservative rul­ing is that Pyrex and such materials are treated the same as other glassware, and can be kashered simply by washing. The Orthodox stand on Pyrex, on the other hand, is that it and other glassware that has been used for baking cannot be kashered, and must be re­placed.

There are two ways to kasher glasses: by simply washing them and waiting 24 hours, or by milui v'irui [soaking]. This method, soaking, is primarily used to prepare glass­ware for Pesach, but it may also be used when going from an unkosher to a kosher kitchen. Place the glassware in a single layer (no stacking) in a large container (this may be done in a cleaned bathtub that hasn't been used for 24 hours). Cover with water completely. The glassware needs to soak 72 hours, but you must change the water after 24 hours and again after 48 hours. At the end of the 72 hours, drain and wash the glassware.


The kashering method used for most foodware is hag'alah [scouring or boiling]. It is used primarily for dishes and flatware made of metal, stone, wood, and rubber. According to Conservative halakhah (Jewish law), it can also be used for hard plastic, such as Melmac (the brand name for melamine). Orthodox opinion on this issue varies. Some say plastics are kasherable, some say they are not. Since most plastics are not used in an oven or over a direct flame, there is a certain amount of leniency here.

Hag'alah means "boiling." You need a very large pot for this, ideally one dedicated to the kashering process. When we kashered our kitchen when I was a kid, my mother pur­chased a huge pot, larger than any we'd ever used. Part of the koshering process calls for a large stone, and my mother asked for the permanent loan of a heavy, smooth stone I had found on the school playing fields some months before. The stone can serve two purposes. One, it helps maintain the heat of the boiling water as objects to be kashered are added. And two, it is used to kasher large pots, by dropping it into the pot in order to cause the water to overflow down the sides.

Did you like this article?  MyJewishLearning is a not-for-profit organization.

Please consider making a donation today.

Lise Stern

Lise Stern is a food writer living in the Boston area.