's Kashrut Class - Kashering

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Lesson III - Kashering

If a mistake is made it does not necessarily render the utensil unkosher. And even if it does render the utensil unkosher, you do not have to throw it out. Most kitchen equipment can be rekashered.

Items can be unkashered by using unkosher food in them (like forbidden meat) or by accidentally using a milchig utensil for fleishig food (or vice versa). The food and the utensil becomes immediately unkashered if either the food or the utensil is hot. The food and utensil becomes unkashered after 24 hours if both the food and utensil are cold. Traditionally hot spices and pungent vinegar (and I guess jalapenos) are consider always hot in this respect. There is a rule called batel beshishim that states that accidental mixing of up one sixtieth part is considered too small to unkasher food or utensils (This is accidental, intentional mixing renders unkosher).

There are two traditional ways of kasher ing. By boiling or by flaming. The first required immersing the vessel in boiling water; the second by heating. Utensils used for liquids are kashered by boiling, those use for dry foods are kashered by flaming. There is a third traditional way of kashering called planting. This is done by placing the utensil in the ground for a prescribed amount of time. This method is non-halachic and hould not be used. Since this is a traditional practice of some roups, those groups do consider this a valid method of kashering.

To kasher by boiling the following steps are used:

  1. The item to be kashered must first be thoroughly cleaned and scoured.

  2. The item (and the vessel it is to be immersed) must not be used for 24 hours.

  3. Boil water in the immersion vessel til it roils.

  4. Totally immerse the vessel in the immersion vessel. The vessel must not touch the sides on the immersion vessel. Let go of the vessel (so water can get to where you are holding it).

  5. If the vessel to be kashered (like a very large pot) does not fit in another other vessel, boil water in it til it roils so water spills over it sides. It is traditional to put an object heated to over 212 F (traditionally a rock) to cause to water to overflow without cooling the water.

  6. Remove the vessel and rinse in cold water.

  7. The pot used for kashering should then be rekashered (step 5)

Items that are to be flamed are kashered similarly, only are heated til red hot.

Items of metal, enamel, wood, teflon, and plastic can be kashered. Items with loose handles and deep crevices must be carefully cleaned before kashering.

Glass is considered non-absorbing, and thus does not have to be kashered. This means it would be all right to use glass plates for milchig and fleishig foods, but this is frowned upon. Pyrex (and other cooking glass) is a special category. The Orthodox believe that glass might absorb at high temperature and do not use it for both. The CJLS has (with the help of that disinterested third party Corning Glass) determined that pyrex does not absorb, and can be used for both. Rabbi Sack's (and also my) policy is not to use pyrex for both.

China, porcelain, pottery, and earthenware can not be kashered. There is an exception (which I mention with great trepidation). China of great personal worth (Grandma's for example) can be set for one year and be considered kosher. You MUST consult a rabbi before doing this.

Metal sinks can be kashered by scouring and then pouring boiling water in them. Some say the sink should be filled with boiling water. In either case, care must be taken to make sure the whole sink is affected. Make sure the water is still boiling as it hits all parts of the sink.

Formica and metal counters are kashered by first scrubbing, then, after a 24 hour wait, pouring water on them. Wood counters are first scrapped or sanded.

Ovens are kashered by scouring clean and then leaving at their highest temperature for over 30 minutes. Use of a blow torch are only for fanatics. Ranges are first scoured, then have their burners turned on till they glow or till a piece of paper will singe if touched to the burner. Selfcleaning ovens can naturally kasher themselves. There is a question whether continual-cleaning ovens do.

Small appliance should have the parts that might contact the food kashered by boiling. The body or motor of the appliance should be carefully cleaned. Special attention should be paid to the crevices.

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Last updated on Aug 1, 1999 at 10:01 PM

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copyright 1999 - Steven Ross Weintraub