During Pesah, we do not use the same cooking utensils or tableware that we use year-round for Hamets. Why? Because although the utensils in which we cook Hamets might be clean, without any visible Hamets residues, their walls or surface might be impregnated with a Hamets substance, which, if not removed, will be reabsorbed into the food we would cook for Pesah. It is customary then, and most recommendable, to have a separate set of dishes, cookware and tableware for Pesah. If this is not possible, one can still use the year round utensils after a process known as hag’ala, a virtual sterilization that removes Hamets residues from within the utensils surface.
Before we do the hag’ala we need to make sure that we clean the utensils and have removed all visible residues of Hamets. The hag’ala then, will expel the Hamets absorbed in the walls of the utensil, by exposing it to heat. The removal of food residues will happen upon the same conditions in which the absorption occurred in the first place (kebol’o kakh polto).
Some examples of hag’ala:
Metal: Metal tableware like forks, spoons or knives, have to be thoroughly cleaned and then immersed in a pot of boiling water. Afterwards, they need to be washed with cold water and then they can be used for Pesah. Hot water opens the pores of metal, allowing the removal of any absorbed Hamets. Cold water closes the pores back.
Glass: According to the Sephardic tradition, glass utensils like cups or plates, used throughout the year for Hamets should be thoroughly washed and then, they can be used for Pesah without any further hag’ala. A glass utensil does not absorb anything thru its pores and therefore there is nothing to remove from its walls. This is applicable even when the glass utensil was used at high temperatures to serve hot Hamets food or even to cook Hamets food. It should be noticed that this Halakha is different for the Ashkenazi custom.
Porcelain (kele heres): Ceramic, pottery or porcelain china and tableware that we use throughout the year for Hamets should not be used for Pesah. They are an exceptional case, because Hag’ala cannot sterilize them completely. Why? Because the way these utensils absorb food in their walls and expel food from their walls is erratic. Therefore, year round porcelain or ceramic utensils should not be used for Pesah.
Cold: Since absorption takes place only at high temperatures, if a utensil was used to serve only cold food, it could be used during Pesah after thoroughly cleaning it, without any hag’ala.
Sink and counter-tops: The sink, counter-tops and kitchen-tables should be thoroughly cleaned before Pesah from any possible Hamets residue. Since we usually don’t place hot food on these surfaces, and these surfaces are not porous, cleaning them thoroughly would be sufficient. Still, following Rabbi Obadia Yosef z”l opinion, it is recommended to pour boiling water on them as an extra precaution. A regular dinning table, wood or glass, should be just thoroughly cleaned. It is customary to cover it with a new tablecloth for Pesah.
Dishwasher: Before Pesah, the dishwasher should be thoroughly clean of any visible food’s residue. Then it has to run on an empty cycle with detergent and without dishes. Thus, the dishwasher becomes ready for Pesah use. Rabbi Eliyahu Ben-Hayim recommends to replace the dishwasher’s racks or to use some added base to cover the racks.
Oven: The oven should not be used for 24 hours. Then we must thoroughly clean it before Pesah to remove any visible Hamets residue. Then, 1. if it is a self-cleaning oven, one self-clean cycle will be enough to have it ready for Pesah. 2. if it is not a self-cleaning oven, after we thoroughly clean it, we should run the oven on the highest temperature-setting for about an hour, including the racks. Then the oven is Kosher for Pesah.
Microwave: We should thoroughly clean the microwave before Pesah to remove any possible Hamets residue. Then, we take a bowl of water with some detergent or soap in it, and we let it boil inside the microwave for a few minutes, until the microwave walls are filled with its steam. This vapor would expel all absorbed Hamets residues, rendering the microwave Kosher for Pesah. If you can’t do this and you need to use a year-round microwave during Pesah, you should cover the food in a hermetic plastic container, Ziploc or any other airtight microwavable cover.