Q. On question 2969 regarding if one can use olive oil that was left uncovered overnight for lighting the Chanuka menorah, and Horav Shlomo Miller’s Shlit’a opinion is that after the fact, one can use it. Now, many have a tradition that they fill the cups of the menorah with oil, and then after enough time has elapsed, they turn off the lights and save the oil for tomorrow. Would not that make that leftover oil on the menorah overnight disqualified at least lechatchila (on the onset)?
A. In a Prior question 682, the Rov was more lenient and ruled that one can you use oil for Chanuka lighting that was left uncovered overnight for a number of reasons. Firstly Poskim disagree whether in our days we should discard certain liquids that were left uncovered or Mashkim Megulim. The main reason for their prohibition is the possibility of their contamination by poisonous snakes (Avoda Zara 30a, Chulin 9b) and since that rarely occurs in our populated cities, we are lenient (Shulchan Aruch Y.D. 116:1, Mishna Berura 160: 23.) However, some Poskim do remain stringent (Pri Chodosh and Pri Toar, quoted by Birkei Yosef and Aruch ha-Shulchan Y.D. 116:1.) There are other issues of ruach ra’ah or a spirit of impurity involved in liquids left uncovered .
It is important to know that when Mashkim Megulim are prohibited they may be so even when left uncovered and unsupervised for a short time, not only overnight.
Poskim also differ if prohibited or non-kosher oil can be used for Chanuka lights and many are lenient (Sdei Chemed – M. Chanuka 14, Kaf Hachaim 673: 11, Beis Shlomo O.H. 10: 108). Others are stringent (Sefer Hachaim quoted by Daas Torah 673).
However the main reason that oil left uncovered is undoubtedly permitted is that there is no Mashkim Megulim issue on oil, since snakes don’t drink from it (Chulin 49b, Bais Yosef Y.D. 116, Yemei Chanuka p. 71).
The Rov further added, that once it was placed in the menorah and lighted, it is not considered liquid food and therefore not affected.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit’a