The process of "Hag'ala," immersing a utensil in boiling hot water, has the effect of expelling the taste from the walls of the utensil, thereby divesting it of its previous Halachic status. Thus, for example, a utensil that had been used with non-kosher food can be made usable with kosher food through Hag'ala, as all the particles of forbidden food are extracted from the walls of the utensil.
May one convert a utensil from dairy to meat, or from meat to dairy, through the process of Hag'ala? If, for example, a person is hosting a dairy meal and does not have enough dairy silverware, may he perform Hag'ala on several meat utensils and then use them for the dairy affair?
The Magen Avraham (Rabbi Avraham Gombiner, Poland, 1637-1683) records the practice to forbid converting dairy utensils to meat and vice versa, and he offers a reason for this custom. If we would allow converted utensils in this manner regularly converting one's utensils will likely result in confusion and uncertainty regarding the status of his utensils. If a person uses his utensils for both meat and dairy by performing Hag'ala, he will often be unsure as to whether a given utensil was last used for meat or for dairy. As a precaution against this kind of confusion, communities adopted the practice to forbid converting utensils from dairy to meat or from meat to dairy. This is also the ruling of the Chatam Sofer (Rabbi Moshe Sofer, Pressburg, Hungary, 1762-1839).
By contrast, the Chid"a (Rabbi Chayim Yosef David Azulai, Israel, 1724-1806), in his work "Shiyurei Beracha," cites the Peri Chadash (Halachic work by Rabbi Chizkiya Da Silva, Italy-Israel, 1659-1698) as disapproving with this practice. The Peri Chadash argued that after the period of the Talmud, we do not have the authority to enact new prohibitions to safeguard against Torah violations, and therefore one need not abide by this practice to forbid converting utensils from meat to dairy or vice versa. Likewise, according to this view, one may perform Hag'ala on a meat or dairy utensil to make it Parve, and thereafter use it for either meat or dairy.
In practice, Ashkenazim follow the custom recorded by the Magen Avraham, while Sepharadim follow the ruling of the Chid"a, allowing the conversion of utensils from meat to dairy and from dairy to meat.
Summary: Ashkenazim follow the practice to forbid converting utensils from meat to dairy and from dairy to meat through the process of Hag'ala, whereas Sepharadim are allowed to convert utensils from meat to dairy or vice versa.
