Ashkenazim drinking from the glass in non-kosher restaurants

Question

Everyone I know does this, including the strictest. That is, if ordering a cold drink at a non-kosher restaurant or bar, they will have it in the glass the institution provides, not ask for it in a disposable cup. Why is this, if Ashkenazim are supposed to be machmir regarding absorption of taste in glass?

(This page says that drinking from the glass is permitted only derech arai--on an occasional basis--and because the glass is presumed clean and to have only been used with cold drinks. If these presumptions are enough that the glass can be considered kosher, then I don't understand why derech arai would apply; even less if these presumptions are not enough to consider it kosher.)

Answer 1

As you said -- Shulchan Aruch allows one to use a cold, clean non-kosher dish or cup "derech arai" -- occasionally. No taste will transfer, and if only done on rare occasion, we're not concerned you will forget and use it for hot.

(When we say a non-kosher dish, we mean someone baked ham on this plate; this plate went through the dishwasher, cooled off, and now I want to put some cold watermelon on it.)

This would apply to a metal or ceramic cup/plate, which everyone agrees can become truly non-kosher. Ashkenazim therefore apply it as well to glass.

As for what constitutes "derech arai" (the crux of your question), the point is that if I'm not using this glass frequently, I'm unlikely to use it with something hot. Rabbi Hershel Shachter shlit'a is of the opinion that if I use this glass no more than once every thirty days, that's "derech arai." Therefore, if your hotel changes the glasses in your room every day, you're not using the same non-kosher glass for more than one day, and it would be okay.