One important step in preparing for Pesach is Kashering. Once this was a much more significant portion of the preparations, but fortunately today’s society is much more affluent than in previous days, and most people have separate objects set aside specifically for Pesach use. It is much less common today than it used to be to Kasher Bechers or silverware, but certain objects and surfaces are still frequently Kashered, so let’s address the relevant Halachos.
To understand the basic principles of Kashering, we have to start with some basic Halachos. Not only is it forbidden to eat Treif foods, or Chametz on Pesach, it is equally forbidden to ingest Kosher foods that have absorbed flavor from non-Kosher or Chometz products. A simple example of this would be that if one made a Cholent with non-Kosher meat, the potatoes are also forbidden to eat. it is also assumed that pots and utensils absorb taste and secrete it into the following food when hot. Consequently, if one would cook his Pesach food in a Chametz pot, the food would become forbidden to eat on Pesach. To avoid this problem, any items used with hot Chametz that are intended to come into contact with Pesach foods must have all of their flavor removed. The general rule of thumb is that the manner the taste entered the food is the effective method for removing it.
There are two basic methods to accomplish this. If the object absorbed flavor from a direct fire, it requires a direct fire to Kasher it. This is called Libun. If the Chometz was used with liquid, then the utensil needs to be immersed in boiling water to remove this taste. This is called Hagala. Furthermore, if the Chametz was cooked in a boiling pot, it must be Kashered in a pot on the fire. While if the hot Chametz was merely poured on the item in question, pouring boiling water is sufficient. These two processes accomplish very distinct outcomes. Libun burns out all of the Chometz flavor and also incinerates any remaining residue; however, Hagala merely extracts it into the water and dilutes it. We will mention some practical differences soon.
Consequently, if one wishes to Kasher oven racks or stove grates for Pesach, they require being heated to nearly 1000°F until the item glows red hot. The simplest way to accomplish this is to leave them inside an oven while running the self-clean cycle. If one does not have such a feature in their oven, a blow-torch may be necessary. Care must be taken that every inch of the object being Kashered is heated until it glows, merely waving the flame over the item as many services do is worthless. This should not be attempted by someone who is not experienced in the procedure. It may be possible to cover the stove grates with heavy-duty aluminum foil an light all the burners until a very high temperature builds up under the foil. However, this may damage the finish and components of the stove-top.
For items that were not used directly over the fire, such as silverware, immersion in boiling water is sufficient. However, there are numerous conditions that do not apply to Libun. The item to be Kashered must be spotlessly clean, as any residue will not necessarily be removed by the immersion and will also impede the extraction of previously absorbed tastes. Furthermore, the object should not have been used for any hot process for at least 24 hours before Hagala. Additionally, after Hagala, the utensil should be rinsed in cold water.
The most common application of Kashering today is kitchen surfaces. For those of us who are not privileged to own a dedicated Pesach kitchen, the counters and sinks require Kashering. However, due to the composition of most countertops and their construction, this is not a practical solution. Even marble and granite counters are generally not pure stone, they contain bonding agents that may have a status in Halacha of earthenware which cannot be Kashered. Additionally, the seams and joints create intractable problems. Formica is similarly problematic. Rather, the advisable solution for counters is to cover them with an impermeable and durable layer. Contact paper tends to tear, very thick aluminum foil and linoleum are much better. Once the surfaces are being covered properly, there is no need to Kasher them.
Ceramic sinks cannot be Kashered, and a plastic tub should be inserted inside the sink after a thorough cleaning. Stainless-steel ones may theoretically be Kashered, although the process can be dangerous to the uninitiated. This is done by means of pouring boiling water over the surfaces after a thorough cleaning and waiting a full day. The water must still be boiling when it is poured from the pot; the simplest way to accomplish this is to use an electric urn and pour from it while it is plugged in. Effort should be made to pour directly on every inch of the surface of the sink, on the bottom and all the sides. This is tricky, and it is often recommended to cover even stainless sinks.
Obviously, this is merely a brief overview of the Halachos and specific questions should be directed to your Rav. If you wish to ask me further personal questions, feel free to inquire.