From a kashrut point of view, a modern dishwasher is by far the most complicated appliance in the kitchen. What goes on inside is the following:
- Some amount of hot water is sprayed around on the dishes inside.
- At some point, soap is released, typically from a compartment in the door. This soap gradually mixes in with the spraying water.
- In some dishwashers, a heating element heats the water inside to a high temperature, possibly even yad soledet bo.
If the dishwasher heats water to yad soledet bo, then the dishwasher is acting like an oven and is "cooking" the dishes inside. Ashkenazic Jews therefore restrict use of the dishwasher to either meat or dairy dishes.
So what if you make a mistake and put a meat dish in your dairy dishwasher or vice versa?
This exact case is brought in the Shulchan Aruch, though in a large vat of boiling water used for washing dishes rather than in a dishwasher. For both Ashkenazic and Sephardic Jews, b'dieved we say that all the dishes involved remain kosher. We say this for several reasons:
- There is soap, so all foods and tastes involved are lifgam.
- The dishes never sit in or soak in the water, thus any tastes that transfer go indirectly by way of the sprayed water or steam in the dishwasher.
- The spraying of water is not considered cooking but rather irui kli rishon (or possibly even irui kli sheini depending on the temperature).
Thus if you find that you accidentally washed your dairy dish with your meat dishes in the meat dishwasher, everything is permitted b'dieved. For similar reasons, if you find a meat dish in your cabinet among the dairy dishes or vice versa, everything remains kosher.
Similarly, if you accidentally washed your pareve dish with your meat dishes in the meat dishwasher, they remain pareve. Whether or not you can do this l'chatchila is debatable; discuss it with your rabbi.
- Shulchan Aruch Yoreh Deah 95:3-4
Questions to ponder: