Laws of Koshering (Hag’alah and Libun)

The utensils that we use to eat our food must be kosher. Sometimes these utensils can become unkosher as described below. There are a few methods of koshering, and one must be sure to use the appropriate method for the right utensil. One method is called Hag’alah. The idea of Hag’alah is to remove any unkosher taste that may have been absorbed in the walls of the utensil. Another method is Libun. The idea of Libun is to burn out any taste that may have been left in the walls of the utensil.

  1. A utensil can become unkosher if it was used to cook milk and meat at the same time, to cook milk and meat separately, if it was used to cook non-kosher food, or for Passover, if it was used prior to Passover for Chametz (wheat or barley or any of the 3 additional grains). Flavor from the cooked foods can remain in the walls even after being washed, and it can add flavor to food cooked in that utensil afterwards.
  2. The only time we are required to apply the Koshering Process is on items that were used directly on the fire (Kli Rishon), or are in contact with hot foods that were directly on the fire (Iruy Kli Rishon).
  3. In order to kosher the utensil, it must first be determined how the utensil was used when it became unkosher. If there was no liquid in the utensil, Libun is required. Example: The pan of a cake containing non-kosher ingredients that was baked in the oven requires Libun. If there was liquid in the utensil or if the utensil did not come in direct contact with the fire (Iruy Kli Rishon), Libun or Hag’alah would be required (see below). Example: A pot of soup with non-kosher ingredients was cooked on the fire, and a metal spoon was used to stir the pot. Both the pot and the spoon now require Hag’alah.


  1. You take the item and drop it into boiling water and then remove it and put it under cold water. Make sure the entire item gets to the boiling water, even if you need to turn it around and immerse it again. If the item to be koshered is a pot, you may fill the pot with an inch of water and just steam it up with the cover on. You then rinse it under cold water.
  2. For Ashkenazim only, Koshering is only done after the item to be koshered and the pot used for Koshering were left unused for 24 hours. Bediavad, (if it was already done) it is kosher anyway. Sephardim will require this only on items that were used to cook non-kosher food or milk and meat that was cooked together. Chametz or milk and meat cooked separately, can be koshered right away.
  3. Before Koshering, the utensil must be properly cleaned. If there was extra caked-on food that you cannot remove, which can often build up in cracks by the handle, just put detergent and/or bleach on it to render that food inedible.


  1. Libun is performed by putting the utensil on the fire until it gets hot.
  2. Libun can be performed by putting the utensil in the oven for half an hour.
  3. The following is a list of items and the specific Koshering Process required:
  4. Metal Pots, Metal pot covers, soup ladles, utensils used in cooking, silverware (Metal), all can be koshered with Hag’alah, described above.
  5. Frying pans, kitchen grills, and barbeque grills can be koshered by putting it on the fire without anything in it, until it gets pretty hot. 3 to 4 minutes will usually do the trick. No need to burn the pan.
  6. Baking pans can be koshered by putting them in the oven for half an hour on the highest flame.
  7. Glass, plastic, glazed china, glazed dishes, Corelle, Pyrex, Corningware, or glazed earthenware do not need any Koshering, since they do not retain any flavor.
  8. Ovens, toaster ovens, and convection ovens can be koshered by putting them on the highest flame for half an hour. If they have a self-cleaning option, running the self-cleaning process is certainly good.
  9. Warming drawers do not need to be koshered if they do not normally exceed 125 degrees Fahrenheit.
  10. Microwave Ovens can be koshered by putting a bowl of water on the highest setting for ten to twenty minutes (depending on the power of your microwave).
  11. Klei Cheres (clay type pots, similar to some flower pots) that are not glazed cannot be koshered, because the flavor it retains cannot be removed. If they are glazed, then it wouldn’t require any kashering, since the glass does not absorb the flavor.
  12. Sinks, refrigerators, trash cans, counters, dishwashers, stovetops, tables, cutting boards, mixmasters, silver kiddush cups, and anything not used with hot foods from the fire do not need any koshering.

does this mean serving spoons does not need to be koshered for passover?

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Depends where it was serving from. Very often a serving spoon is used to take out of the pot that was in the oven or on the fire. It’s dependent what you used it for.

Hello, Rabbi. I am confused about item #12 on the list, to the extent that it indicates that no kashering is required for stove tops. I usually clean my ceramic cooktop very well and then run it at the highest setting for 10 minutes and wipe off any residue that comes off the area where the burners are (because, frankly, I am not sure what else I can possibly do to kosher it). Is this “burning off process” required, or is just cleaning it enough?

On a related note, my cooktop is a drop in ceramic cooktop, and crumbs can get caught underneath it (but the only way to reach the crumbs would be lift out the ceramic cooktop (which I have done every year, but it is quite difficult and sometimes even dangerous when the cooktop drops because I can’t hold it up by myself). Is this step required (if I know the crumbs are under there)?

Thank you!!!

Just clean it.
If the crumbs are under the ceramics, in a way that no pot will get near the crumbs, it won’t render the food cooked in the pot unkosher. If you know there are crumbs, you’re supposed to remove them

Regular metal flatware, used for eating, does not usually come into contact with a kli rishon.

Does it require hag’alah anyway?

Thank you for all your work…

Technically not for Sephardim, but most people do hagaalah