Kelim into which cold ḥametz has been placed are kashered by rinsing them. For example, beer mugs are kashered for Pesaḥ by rinsing them, even though beer is ḥametz, because as long as the ḥametz in a kli has not reached the temperature of yad soledet, its residue adheres only loosely to the kli, and it can be removed by rinsing. Certainly, then, plates and bowls into which ḥametz cakes were placed are kashered by cleaning them, because in addition to the fact that the pastries are not hot, they are also dry, and without moisture, flavor does not adhere to a kli. However, one must remove crumbs that may remain on the kelim.
But if the beer was left in a mug for 24 hours, according to many, this constitutes kvisha (“pickling,” or the absorption of taste through prolonged soaking) occurs, and the Sages said: “kavush ki-mevushal” (pickling is akin to cooking). That is, pickling imparts flavor into foods just as cooking does, and according to many, it even imparts flavor into kelim (Peninei Halakha: Kashrut 35:9). Therefore, it is forbidden on Pesaḥ to use kelim in which beer was left for 24 hours.
Kelim that have absorbed taste via kvisha can be kashered through hagala in boiling water, for if hagala is effective on kelim used for cooking, it certainly works on kelim used for pickling. Moreover, since kvisha is a milder form of absorption, one may kasher such kelim by soaking them in water for three 24-hour periods – that is, by soaking the kli in water for 24 hours, replacing the water, soaking it for another 24 hours, replacing the water again, and soaking it for another 24 hours. Of course, it is generally faster and easier to kasher these kelim by means of hagala in boiling water, but kelim that are liable to be damaged by boiling water may be kashered in this manner.
An alcoholic beverage like whiskey, according to some poskim, has the effect of kvisha and imparts the flavor of the whiskey into the kli within 18 minutes. Thus, if one wishes to use this kli on Pesaḥ, he must first kasher it by means of hagala or by soaking it in water for three 24-hour periods.
There is a dispute among the poskim regarding the degree to which kelim absorb taste via kvisha. Some maintain that kelim absorb taste from kvisha just as from cooking (Issur Ve-hetter Ha-arokh, Shakh, and Pri Megadim). Others maintain that kvisha causes kelim to absorb flavor only in their outermost layer (Taz). Still others maintain that only wooden and earthenware kelim absorb flavor through kvisha, but not metal kelim (Kereti U-feleti, Erekh Ha-shulḥan). Above I adopted the stringent view, because this is the accepted ruling, and so it is proper to accept it in practice le-khatḥila. As a matter of technical law, however, the halakha follows the lenient view with respect to glass and metal kelim.
Even though an earthenware kli that absorbed ḥametz during the cooking process cannot be kashered through hagala, if such a kli absorbed flavor through kvisha, it can be kashered by means of hagala or by soaking it for three days, as explained in SA 451:21.