kalau śūdra-sambhavaḥ. It is to be understood that there are no brāhmaṇas in this age because those who claim to be brāḥmaṇas simply on the basis of birthright do not have the brahminical qualifications. However, even if one is born in a non-brāhmaṇa family, if he has the brahminical qualifications he should be accepted as a brāhmaṇa, as confirmed by Śrīla Nārada Muni and the great saint Śrīdhara Svāmī. This is also stated in Śrīmad-Bhāgavatam. Both Nārada and Śrīdhara Svāmī completely agree that one cannot be a brāhmaṇa by birthright but must possess the qualities of a brāhmaṇa. Thus in our Kṛṣṇa consciousness movement we never offer the sannyāsa order to a person whom we do not find to be qualified in terms of the prescribed brahminical principles. Although it is a fact that unless one is a brāhmaṇa he cannot become a sannyāsī, it is not a valid principle that an unqualified man who is born in a brāhmaṇa family is a brāhmaṇa whereas a brahminically qualified person born in a non-brāhmaṇa family cannot be accepted. The Kṛṣṇa consciousness movement strictly follows the injunctions of Śrīmad-Bhāgavatam, avoiding misleading heresy and manufactured conclusions.
Ref >> Srila Prabhupada Vani.