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Rav Yosef

One of the most interesting questions about Pesach Prepping has to do with GLASS. Can glass bowls, serving dishes, drinking vessels, be kashered for Pesach? If they can be, how? Or is it possible that they don't even need to be kashered at all?

The most basic approach taken to the Halachic status of glass is the one taken by the Shulchan Aruch, an approach that is followed by Sephardim to this day. The Shulchan Aruch adopts the Talmudic opinion that glass is simply non-porous as far as Halacha is concerned, and that as a result glass is simply impervious to "becoming anything", and is therefore never in need of being kashered. In this approach, glass simply cannot become treif, or hametz-dik, or milchig (dairy) or fleishig ("meaty"), regardless of whether it is an item of table glass or a baking pan. Any glass implement at all can simply be well-cleaned, and then used for Pesach.

But the Ashkenazic tradition on these matters is more complicated. Though in the laws of kashrut the Rama (our Ashkenazic Halachic benchmark) does not register disagreement with the Shulchan Aruch's approach, in the laws of Pesach he favors and codifies a more stringent practice, actually equating glass with the most porous of substances, namely earthenware. The discrepancy in Rama's writings between the laws of kashrut and the laws of Peach is variously explained, with some (famously among them, Rav Moshe Feinstein) explaining that in general Rama agrees that glass is non-porous, and that he only takes a more stringent approach regarding Pesach. At the other extreme are those who take the position that Rama believes that glass is always to be treated as being porous-like-earthenware, and having said so in the laws of Pesach simply didn't bother to repeat himself in the laws of general kashrut. And there are yet other interpretations of the Rama that occupy the middle space between these two extremes. (More on this when we start running "Kashrut Kurrency" :)

But to return our focus to Pesach, here's the relevant passage from Orach Haim, 451:26. The Shulchan Aruch writes there, that

Glass vessels, even if one stored [hametz] inside them for an extended amount of time, and even if they were used with hot [hametz] food, do not need any kashering, because they do not absorb. Normal washing is sufficient for them.

To which Rama adds:

There are those who are stringent and say that even hag'alah (koshering via boiling water) does not work for glass objects, and such is the practice in Ashkenaz and in in these lands. (Bolded, mine)

It is thus clear that by Ashkenazic practice, if glass became hametzdik either through having had hametz baked or cooked in it, or through having had hot (above 115 degrees Fahrenheit) hametz food served in or on it, or through having had "cold" hametz stored in it for a period exceeding 24 consecutive hours, then we simply put it away for Pesach, period. And in general terms, this is indeed what we do.

  1. You are likely familiar with the practice of kashering some kinds of glass through soaking them in water for 72 hours, changing the water at the 24 and 48 hour marks. This is a method of kashering that is originally mentioned in connection with earthenware barrels that have stored non-kosher wine in them for an extended period of time. The question is: How and under what circumstances did this practice migrate to kashering glass for Pesach?
  1. What about glass utensils that are not hametzdik in any way? In other words, glass items that you've used throughout the year, but which have NEVER EVER absorbed hametz, neither through contact with hot hametzfood, nor through having stored cold hametz?


In order to tackle the first question, we need to remember that rabbis have generally understood that they are responsible not only for interpreting the Halacha, but also for creating a system that people could - in real life - actually observe. In a particular area in which the tendency toward stringent interpretation is prevailing (as is true in the laws of Pesach), corrective remedial measures must sometimes be taken. In our context this meant rabbis pre-empting what might have become a near-total ban on using year-round glass for Pesach, through creatively borrowing a kashering solution from an entirely other Halachic context (i.e. earthenware wine barrels).

Here's what happened: As we mentioned earlier, the Rama's p'sak to treat glass as a porous substance is to begin with, a major stringency relative to the Shulchan Aruch's stance. But the Rama also took an additional stringent stance regarding Pesach, that when piled onto the first one results in a very severe restriction. Let's now understand this additional stringency of the Rama.

The Shulchan Aruch rules: "All things used for drinking, whether flasks or cups, are permitted after they are washed, whether they are glass, wooden, metal, or ceramic. Even though periodically hot bread is placed in them, since they are usually used for cold things, washing is sufficient, because for every object we follow its usual use. (Bolded, mine)

The Shulchan Aruch's ruling renders it completely unnecessary to replace (cold) drinking glasses for Pesach. But here is the (special-for-Pesach) ruling of Rama:

"However, there are those who are stringent and require hag'alah (immersion in boiling water), and such is the practice."

Now, hag'alah is a workable solution for metal and wood vessels that only have hot hametz placed in them periodically, but as we know Rama has already placed glass into the category of earthenware, which is impervious to hag'alah. Thus, stringency #1 + stringency #2 could leave us with no glass glasses to drink from at all! Enter the later poskim who creatively ruled that to prevent this drastic scenario, we may borrow the kashering method that the Halacha specifies for earthenware barrels that have absorbed via cold storage (not an exact match, but sufficient under these circumstances).

And finally (to question #2), we probably own glassware that has NEVER EVER come into contact with hot hametz. I think of wine glasses (in particular crystal or delicate ones) which you know with certainly you've never used with anything other than wine (which is both cold, and in any case typically kosher for Peach all year round.) These need no kashering at all, as there is simply nothing for them to be kashered from. Now you may say, "yes, but they have been washed with hametzdik dishes". This dishwashing is of no Halachic concern however if either:

(1) as a rule you wash your dishes in water that is cooler than the temperature that would hurt your hands (which is what most of us do), or

(2) [in a dishwasher situation where the water is hotter] you have the regular practice of rinsing the plates before putting them into the dishwasher. This assures that the amount of hametz in the dishwasher is too insignificant to impact the glasses.

To this, add the general leniency of the Shulchan Aruch that the presence of soap effectively undermines the Halachic absorption mechanism, and that you will for sure only be using these wine glasses for cold liquids over Pesach, and the case that you do not need to do any kashering for these glasses is more than sufficient.

Fri, June 2 2023 13 Sivan 5783