Electrical appliances such as blenders and mixers are occasionally used to mince and mix hot and sometimes sharp foods.
Regarding such appliances, one must follow the established principles and always relate to two problems: 1) ĥametz may have gotten stuck in crevices and holes; 2) the taste of ĥametz may have been absorbed into the walls of the appliance.
If such an appliance was used with cold, non-sharp foods only, there is no problem of absorption, but there is still concern that food particles got stuck in its crevices. It must therefore be cleaned thoroughly. If there are grooves in which food particles remain, the appliance may not be koshered; alternatively, it may be soaked in soapy water or in some other agent that renders the residual food unfit for canine consumption.
Mixers have holes designed to provide ventilation for the motor, so that it does not overheat. Flour and pieces of dough splatter into these holes, and there is concern that, when used with Pesaĥ foods, pieces of ĥametz will fall into the food. In order to kosher a mixer, one must open the motor compartment and clean it thoroughly, or plug up the holes completely. This rule applies to any appliance about which there are similar concerns.
If such an appliance was used with hot foods, and one was not cautious about ĥametz throughout the year, there is concern that it has absorbed the taste of ĥametz. Therefore, one must perform hagala on all parts that came into contact with hot food.
And if such an appliance was used with sharp foods, and one was not cautious about ĥametz throughout the year, even if the foods were always cold, there is concern that contact with the strong sharpness caused the taste of ĥametz to be absorbed by the appliance. One must therefore perform hagala on all parts that came into contact with food (see SA YD 96:1; Kaf Ha-ĥayim ad loc. 1).
If the appliance was used for kneading dough, according to the Sephardic custom hagala is necessary, and according to Ashkenazic custom light libun is needed (based on SA 451:17).