The best food is the remnants of what is offered to the Supreme Personality of Godhead . In Bhagavad-gītā the Supreme Lord says that He accepts preparations of vegetables, flour and milk when offered with devotion. Patraṁ puṣpaṁ phalaṁ toyam.

Of course, devotion and love are the chief things which the Supreme Personality of Godhead accepts. But it is also mentioned that the prasādam should be prepared in a particular way.

Any food prepared by the injunctions of the scripture and offered to the Supreme Personality of Godhead can be taken even if prepared long, long ago, because such food is transcendental.

Therefore to make food antiseptic, eatable and palatable for all persons , one should offer food to the Supreme Personality of Godhead.

BG 17.10 Purport by HDG A.C Bhaktivedanta Swami Prabhupada