A pot in which meat was cooked may not be used to cook milk. If consecrated meat was cooked in it, it may not be used to cook non-consecrated meat. And if it was used, it all goes by the giving of flavour.
Basar - Meat - anything from kosher mammals or birds (i.e. not fish or locusts).
Chalav - Milk / Dairy - anything that is derived from the milk of a kosher animal
Pareve - neither meat nor dairy
Treife - non-kosher (lit. torn up)
milchig / chalavi - dairy stuff
fleishig / basari - meaty stuff
Ba'ayin - actual foodstuff
Ta'am - Taste / Flavour
Ta'am Lifgam - a detrimental / bad flavour
Asur vs. Mutar - Forbidden vs. Permitted
Lechatchila vs. Bedeiavad - in the first place / ideally vs after the fact / non-ideal
(א) קדירה שבשלו בה בשר לא יבשלו בה חלב. ובו סעיף אחד:
קדירה שבשל בה בשר לא יבשל בה חלב ואם בישל בה בתוך מעת לעת אסור בנותן טעם (וצריך לשער נגד כל הקדירה) אבל אם שהה מעת לעת קודם שבישל בה הוי ליה נותן טעם לפגם ומותר התבשיל אבל הקדרה אסורה לבשל בה לא בשר ולא חלב:...
(1) A pot in which meat was cooked, one may not cook in it milk. And if one cooked [milk] in it within 24 hours, it is forbidden on account of “giving taste.” And one needs to measure [for negation by 60] against the entire pot. But if it sat for 24 hours before one cooked in it, [it is a case of] “giving detrimental taste,” and the food [cooked in it] is permitted, but the pot is forbidden to cook in either meat or dairy...
בשר וגבינה שנגעו זה בזה מותרים אלא שצריך להדיח מקום נגיעתן ומותר לצור אותם במטפחת אחת ולא חיישינן שמא יגעו זה בזה:
דין מאכל חריף שנחתך בסכין של בשר. ובו ה' סעיפים:
צנון או סילקא שחתכם בסכין של בשר בן יומו או שאינו מקונח אסור לאכלם בחלב עד שיטול ממקום החתך כדי נטילת מקום שהוא כעובי אצבע או שיטעמנו ולא יהא בו טעם בשר שאז מותר בהדחה ויש אומרים דהוא הדין לאינו בן יומו והוא מקונח. ...
1) Radish or beets that were cut with a meat knife, used that day or that was not cleaned off are not allowed to be eaten with dairy, until a slice is removed from the location of the cutting that is an "amount to be taken." This amount is equivalent to the width of a thumb. Or let it be tasted, and if it does not have the taste of meat it can be eaten with dairy with mere rinsing. There are those who say that this is also the rule with a knife that was not used that day and was cleaned off. ...
Is the food hot or cold?
Is the flavour good or bad?
Is it spicy or sharp like an onion?
Was the utensil clean or dirty?
When was the utensil last used?
What was the volume of the utensil vs. the volume of the dish?
How many steps removed from the food is the current situation?
(21) Eleazar the priest said to the troops who had taken part in the fighting, “This is the ritual law that the Eternal has enjoined upon Moses: (22) Gold and silver, copper, iron, tin, and lead— (23) any article that can withstand fire—these you shall pass through fire and they shall be clean, except that they must be cleansed with water of lustration; and anything that cannot withstand fire you must pass through water.
Rav Huna, son of Rav Yehoshua, said: A wooden ladle should be purged in boiling water in a primary vessel He holds in accordance with the principle: As it absorbs the flavor of the forbidden substance, so it emits it.
1. Dishwashers made for residential use, whether metal or plastic may be kashered from treife to kosher and from hametz to Passover. The procedure is as follows: The dishwasher should be thoroughly cleaned paying special attention to the filter and the silverware rack. The dishwasher should not be used for 24 hours. The dishwasher should be run one time at the highest temperature with soap in the soap dispenser and in the main dishwasher.
2. The dishwasher may be used to wash meat and dairy dishes consecutively. While we do not require new racks, we do require waiting 24 hours between using the dishwasher for meat and dairy dishes. However, if for some reason the dishwasher was used without the 24 hour waiting period, then b’dieved, we can rely on the soap rendering the taam pagum and the dishes are still kosher. It is strongly suggested that if there is a filter that requires manual cleaning at the bottom of the dishwasher, it be checked to assure there are no pieces of food remaining at the bottom. Also, the silverware rack must also be checked for food residue.
3. Dishwashers may not be used to wash dairy and meat dishes simultaneously.
When I asked Prof. Kraemer about the history of two sets of dishes in the home, he reminded me that I was making assumptions about what “sets of dishes” means. The kinds of utensils we use for eating have changed over time, so while now we may be accustomed to having dinner plates, salad plates, bowls, mugs, glasses, plus a knife, a fork, and a spoon at minimum, this wouldn’t necessarily have been the norm in earlier eras. “In order to have separate dishes, you need to have dishes in the first place,” Kraemer said. For hundreds of years, Jews ate from large bowls and platters shared by the whole family, instead of individual plates. This necessitated far fewer objects in the kitchen, and meant that having duplicates of everything for meat and milk was less of a hassle. This lasted until about the 17th century, when eating technologies began to evolve towards individual portions and plates.
According to Prof. Kraemer, by the time shtetl life was in its heyday, in the 18th-19th centuries, personal flatplates, spoons, knives, and often forks had become the convention, much like what we have today. In observant Jewish communities (both shtetls and urban communities) the norm was to have two sets of dishes, one for meat, and one for dairy.