If one used oil to fry meat and the next day used the same oil to fry something pareve (eg. french fries), is the pareve food considered 'meat'? Is there any differences between Sefardic and Ashkenazic Jews in this regard?
http://www.star-k.org/kashrus/kk-kosher-cons-handbk.htm (footnote 10):
One must also wait six hours if he ate french fries that were fried in oil previously used to fry chicken. Therefore, if one eats french fries (or other deep fried items) prepared in a fleishig restaurant, he should assume that he is fleishig unless the certifying agency of the restaurant indicates otherwise. Similarly, if one is fleishig one may not eat french fries that were fried in oil that was previously used to fry dairy products. When in doubt, consult with the restaurant’s certifying agency.
The Tur (Yoreh De’ah 89) writes that one does not have to wait between a meat dish and a dairy dish if neither one contains actual meat or milk.
The Bach notes that while Semak allows one to eat cheese after foods cooked in meat fat, the prevailing custom is not to do so, and one should not deviate from the common custom. The Rema (89:3) goes further, saying that one must wait after a meat dish just as if he had actually eaten a piece of meat.
Although the Shulchan Aruch is not stringent on this matter, the Beis Yosef (Orach Chaim 173) does mention the stringency, and later authorities (Ashkenazi and Sefardi alike, including the Ben Ish Chai and the Kaf Hachaim) are stringent in this matter.
Eating the fries implies consuming the meaty oil, and therefore one must wait after eating them before milk (Source: dinoline.org).
On the other hand, Rav Schachter ("Basic Kitchen Kashrut" end of shiur) explained that one doesn't need to wait 6 hours after having french fries from a restaurant that fried them in the same deep fryer that was used to fry chicken. This is true if the cook didn't intend for the meat taste to be imparted into the french fries and just uses the same oil for convenience. In that case, the fries aren't even considered tavshil basar. This ruling is based on the Rama YD 89:3, Shach YD 89:19, and Yad Yehuda 89.
Nevertheless, Horah Brurah 89:43 writes that the pot needs to be clean in order for the food to be considered parve and not meat. In the biurim he explains that for Sephardim the idea of the Shach doesn't follow from the Bet Yosef 173:1. Additionally, the Bet Meir 89 argues on the Shach since if the remnant foods are more than sixty certainly that's called a meat dish.
This also disputed between Rabbi Felder and Divrei Moshe whether the deep fried food which was fried in the same oil as meat or chicken was fried in requires the one eating the food to wait six hours. Rav Felder is strict since the Shach was only talking about a pot which was clean but there was a bit of meat remaining unintentionally. Also, teimat yisrael doesn't help since the taste of chicken or meat fat and vegetable oil is very similar.