What is considered "Ketores Zarah"?
Rashi #1: Any Ketores that is donated (other than the prescribed amount that comprises the Ketores Tzibur) is considered Ketores Zarah.
Rashi #2 (in Zevachim, 27b): The Torah only permits the Ketores shel Tzibur morning and afternoon - Any other Ketores is considered Ketores Zarah.
Ramban (citing Targum Onkelos): It refers to Ketores that is made up of any combination of spices other than those prescribed by the Torah in Ki Sisa, 1 or even if one adds spices to those that the Torah prescribes.
Menachos, 50b: Refer to 30:0:2:1.
As laid out in Pitum ha'Ketores.
What are the implications of "Lo Sa'alu alav Ketores Zarah"?
Menachos, 50b: It implies that a Yachid is not permitted to donate the Ketores, and that a Tzibur is not permitted to bring Ketores Nedavah on the Mizbe'ach ha'Zahav. 1
Menachos, Ibid.: And the Pasuk in Ki Sisa, 31:11 "ke'Chol asher Tzivisicha Ya'asu" teaches us that the Ketores Tzibur may not be brought on the Mizbe'ach ha'Olah. See Torah Temimah, note 16.
