Reference for Menachot 36:12

איכא דאמרי אמר רב נחמן לא קשיא כאן בנקמצות כאן בשאין נקמצות

here with the meal-offering of an Israelite. In the case of the meal-offering of an Israelite, from which the handful must be taken, the duty of the priesthood begins with the taking out of the handful; we thus learn that the pouring in [of the oil] and the mingling are valid [even though performed] by non-priests. In the case of the meal-offering of a priest, from which the handful is not taken, the services of the priesthood are required from the very beginning.

Jastrow