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Induction cooking involves an alternating magnetic field in a coil underneath a smooth glass/pyrex surface. This alternating field induces eddy currents in an iron pot placed on the hob. In turn, these currents (due to Joule heating) cause the pot to directly heat up and the contents within them.

The actual glass/pyrex surface heats up as a result of contact with the hot pot. Often, induction hobs have a fail-safe whereby you can only turn on a heating ring when a pot is placed onto it (unlike a typical electric/gas hob). In this sense, it cannot be heated/kashered at full temperature in the same way that an electric/gas hob can be - the glass surface of an induction hob is indirectly heated by the pot.

Is there a procedure to kasher such a surface for Pesach bearing in mind the Ashkenazi stringency not to kasher glass on Pesach?

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  • The concern with glass is the inability to effectively perform hagolah on it. Libun is tstill possible. Most kashrus agencies suggest turning the burners on high for an extended period of time, and then covering the space between the burners (since it can't be kashered, though why this is so eludes me). Mar 29, 2015 at 12:15
  • @IsaacKotlicky I will edit my post to include that some induction hobs can only be turned on when a pot is placed on it. In this sense it is unlinke an electric/gas hob.
    – bondonk
    Mar 29, 2015 at 12:18
  • So why not place a metal plate or somesuch on the burner to activate it for kashering? if the metal gets hot enough for libun, the glass al achas kama vekama? Mar 29, 2015 at 12:40
  • There is still the issue of kashering glass for ashkenazim. Also, induction hobs only work with iron pots, would you need a koshered iron pot to do this?
    – bondonk
    Mar 29, 2015 at 12:43
  • Not a clue. Why not a flat plate of iron on the burner itself? I've never used induction tops personally, so this is unfamiliar ground to me... Mar 29, 2015 at 12:44

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I don't understand these answers. Surely the basis of kashering is to bring the item to a temperature above that that it experiences when cooking. As the glass top only receives heat indirectly (from the pot above), it never reaches a particularly high temperature and therefore does not need hagolah or libun. Or have I misunderstood this.

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  • Hi! Welcome to Mi Yodeya. I recommend the tour, so you see how this site works -- it's different from other sites you may be accustomed to. For example, the spot where you posted is reserved for answers to the original question, and is not for comments/questions on other posts. If you intended this as an answer (that in fact one need kasher such a surface), then that's fine, but then you should probably word it as such.
    – msh210
    Mar 11, 2016 at 18:34
  • " it never reaches a particularly high temperature" - it sure does. Maybe not 100 degrees celcius exactly. But it gets pretty hot. It even turns red.
    – Shmuel
    Mar 28, 2023 at 17:01
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In Peninei Halacha, Rav Melamed permits koshering and using induction cooktops under certain conditions (here):

Induction cooktops: The surface on which the pots are placed is like smooth, impervious glass. However, unlike ceramic burners, in which the heat source is within the ceramic surface, in induction cooktops the heat source is in the pot, which heats up by means of a magnetic field. From the pot, the heat spreads to the food cooking within it and to the surface on which it is standing. Ḥametz is liable to be absorbed into the cooktop via food that overflowed from the pot, some of which can get stuck to the base of the pot and continue to heat up along with it. Such cooktops are therefore kashered by cleaning them and pouring boiling water over them. Kashering them from the food that overflowed and got stuck to the bottom of the pot is based on the principle of ke-bole’o kakh polto: wet the bottom of the pot when they are empty, and heat them up on the cooktop for about 15 minutes. (Below, in section 12, the obligation to kasher glassware is discussed.)

In section 12 (here) Rav Melamed makes a distinction between Ashkenazim and Sephardim vis a vis glass and concludes that:

Many Sephardim follow the lenient opinion and kasher glassware by rinsing it only, and many Ashkenazim have the custom not to kasher glassware. In practice, however, it seems that the middle position, according to which glassware has the same status as metal kelim and can be kashered by means of hagala, is primary. Those whose family custom is to be lenient may maintain their custom, and those whose family custom is to be stringent should maintain their custom.

i.e., Rav Melamed brings a distinction between Sephardim and Ashkenazim. It is acceptable for Sephardim to kosher and use like regular glass, and that ("primarily") Ashkenazi psak would allow it as well.

To counter this, the OU does not allow kashering of glass stovetops, but provides a solution to using one in any case (here):

Glass Stovetop: A glass stovetop cannot be kashered, and therefore must be dealt with as follows:

  1. Clean the stovetop surface well and do not use for 24 hours.
  2. During Pesach, pots should not be placed directly on the stove surface, but rather an aluminum (or other metal) disk should be placed directly under the pots.

One should not cover the entire glass top surface, as this might cause it to overheat and crack.

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Those cooktops can totally handle 212 degree water poured on them. Thus, the Star-K writes:

Induction Cooktop

Before kashering an induction cooktop, it must be thoroughly cleaned and then left unused for at least 24 hours. The cooktop then requires iruy roschin. (Refer to instructions below for kashering a stainless steel sink by using iruy roschin.)

Essentially -- treat it like a stainless-steel sink.

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    This logic is subject to the general dispute of if (ashkenazim in particular) can kasher glass for pesach.
    – Double AA
    Mar 28, 2023 at 15:30

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