halacha - Kashering pot from meat to dairy/parev?

I know I've learned somewhere that you can't kasher a meaty pot for use with dairy (except for Pesach), but I can't find a source for it now. Can anyone provide a source? (The sauce would be a light Alfredo; the source would be somewhere in Yoreh Deah I expect...)

Following on from that, and hopefully to be found in the same source, is my more practical question: can you kasher a pot from meaty to pareve, so that you could cook pasta to be eaten with that yummy Alfredo sauce?

Answer

The Sefer הכשרות by רב יצחק יעקב פוקס explains as follows (chapter 3:5)

• For Sefardim, as long as the item is not ben yomo (has not been used for cooking with dairy/meat) in the last day, it is permissible to change from Dairy to Meat, even lechatchila. Sources: Pri Chadash YD 97:1, Chidah - Machzik Beracha 509:2, Aruch haShulchan YD end of siman 89 and 181:11, Yabia Omer YD 3:4.


• For Ashkenazim the minhag is not to change from one type to the next (Magen Avraham OC 509:11 - since if you get used to changing over, you might make a mistake and kasher a ben yomo pot by mistake) unless it is one of the following circumstances:
  
  
  
  • Sha'at haDechak - Pressing Need/No other choice (i.e.: you need to use the pot for something pressing) (Prim Megadim Eishel Avraham OC 152:13)
  
  
  • Kashering pre-Pesach to get rid of chametz, can switch over from Meat/Dairy (Mishnah Berurah 451:19)
  
  
  • If you will use it for some period of time as a pareve pot before going to the other type (Shu"t Maharsham 2:241, Tzitz Eliezer 9:38)
  
  
  • If it had become treif anyway (ex: it was a milk pot that was accidentally used for meat, when you kasher it you can change it to meat) (Mishnah Berurah 509:25, Shu"t Be'er Moshe 3:105, Maharsham from above)
  
  
  • It hasn't been used for a year+ with its current milk/meat type (Shu"t Maharsham from above)
  
  
  • Received it as a gift and want to change it
  
  
  
  
  


• If you want to kasher using libun you can do so at any time, even for Ashkenazim (Sha'ar haMelech, Hil. Yom Tov, 4:8)

Following from all of that, it seems that if you are Sefardi then as long as the pot is not ben yomo you can kasher to the other type. If you are Ashkenazi then you cant do it unless one of the conditions from above apply (I don't know if wanting yummy alfredo sauce would be considered a pressing need).