A hob is not one surface — it is several parts that have had very different things happen to them, and they are not kashered the same way. That is why a single instruction never covers it.
A gas hob
After it has stood unused for twenty-four hours, clean every part thoroughly. Then:
| Part | Treatment |
|---|---|
| The grates (trivets) that pots sit on | Libun kal — heating |
| Burner heads | Scrub thoroughly, then libun in fire |
| Burner caps, the hob surface, the tray, the knobs | Clean thoroughly, then pour boiling water over |
The logic is visible once the list is laid out: the parts that food actually lands on while directly over flame get heat treatment, and the parts that merely catch spills get poured.
An electric hob or hotplate
Different approach, because there is no flame to use.
Clean thoroughly with a strong degreasing cleaner — every part, including the knobs and into all the cracks and folds where fat collects. Then heat it at its highest setting for a period.
The heat does the work that the flame would otherwise do.
What people get wrong
Treating the whole hob the same. Pouring boiling water over grates that need libun does not kasher them, and it is the single most common error here.
Skipping the knobs and the tray. They are not where you cook, but they are where things spill, and both are named specifically.
The folds and seams. Fat collects where the hob surface meets its frame, and a degreaser and a brush are needed rather than a wipe.
Glass hobs are a separate question
A glass surface does not behave like a conventional hob, and the usual answer is that it cannot be kashered — see can glass be kashered, which covers the reasoning and the alternatives that were considered and rejected.
Before doing any of this, leave the hob unused for a full day. What your particular hob needs is a question for your rav.
Where this comes from
- ספר הכשר כלים, פרק ג — kashering the kitchen and its vessels
- Shulchan Aruch, Orach Chaim 451, with Rema
- Shulchan Aruch, Yoreh De'ah 121-122