One reason why I started this blog way back when was to post answers to frequently asked questions, and this is a perfect example. I often get asked about kashering dishwashers and how to use them for meat and dairy dishes.
I will not go into a full treatment here of the multiple opinions, but I’ve found people seem genuinely shocked when I cite the opinion of the Shulhan Aruch, a usually acceptable source which in this case is relatively lenient compared to other opinions or conventional understanding.
First, here is the relevant source:
שולחן ערוך יורה דעה הלכות בשר בחלב סימן צה
קערות של בשר שהודחו ביורה חולבת בחמין שהיד סולדת בהן, אפילו שניהם בני יומן, מותר, משום דהוה ליה נותן טעם בר נותן טעם דהתירא. והוא שיאמר ברי לי שלא היה שום שומן דבוק בהן. ואם היה שומן דבוק בהן, צריך שיהא במים ס’ כנגד ממשות שומן שעל פי הקערה.
יראה לי שאם נתנו אפר במים חמין שביורה קודם שהניחו הקדירות בתוכה, אף על פי שהשומן דבוק בהן, מותר, דעל ידי האפר הוא נותן טעם לפגם
Shulhan Aruch Yoreh Deah 95:3-4
Meat plates washed in a dairy cauldron, hot enough such that one’s hand burns (the halakhic temperature for absorbency), even if both had been used within one day, it is permitted because it is gives a secondary tasting (noten ta’am bar noten ta’am, too much to detail here). And this is where he says I am certain that there is no fat stuck to the plate, and if there was meat fat stuck, then there must be 60 parts water in the pot compared to the meat fat [such that it would be nullified in batel beshishim]
It seems to me that if one put ashes in the hot water in the pot before one put in the pot, even though there is fat stuck it is permitted because the ashes will ruin the taste.
Kashrut follows a principle of ta’am k’ikar, meaning even the taste of an item (e.g. meat, or a non-kosher food) is equivalent to the item itself, and there are numerous laws regarding how “taste” can transfer. However, if the item in question would be notein ta’am lifgam – give over its taste to detriment i.e. an undesirable addition – then the taste in question would not halakhically absorb. I know it may sound confusing, but this is the best I can summarize Yoreh Deah in a paragraph.[1. And I’m not even getting into the nuances which are themseves debated by halakhic authorities.]
According to the Shulhan Aruch cited above, the addition of “ashes” to a pot of hot water is sufficient to mitigate the taste transference from meat dishes to dairy dishes, even when there is actual residual meat fat stuck to the dish itself. Today we do not use ashes but dishwasher detergent which I suspect also ruins any leftover food such as to make it inedible. Therefore, for the Shulhan Aruch it would be permissible to wash meat and dairy dishes in the same dishwasher at the same time. Furthermore, operating on the very reasonable assumption that dishwashers are only run with some form of detergent, there would be no need to kasher a dishwasher if it has been previously used for non-kosher dishes.
This is not to say the Shulhan Aruch is the only opinion regarding dishwashers – some are more stringent and others are lenient for other/additional reasons.[2. I remember one opinion stating that plumbing pipes ought to be considered a kli sheni. Forgetting which one exactly, but I know I’m not making it up.]
However, it is still useful to know it exists, and useful for me to have a direct link.