In plain words
Food that is half-cooked, tasteless, putrid, kept overnight, leftover, and unfit for yajña is dear to the tāmasa.
Word for word
What [is] half-cooked, flavourless, foul-smelling and kept overnight, and also leftover and unfit for yajña: [such] food [is] dear to the tāmasa.
यातयामं गतरसं पूति पर्युषितं च यत्उच्छिष्टमपि चामेध्यं भोजनं तामसप्रियम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam· bhāṣya
यातयामं मन्दपक्वम् , निर्वीर्यस्य गतरसशब्देन उक्तत्वात् । गतरसं रसवियुक्तम् , पूति दुर्गन्धि, पर्युषितं च पक्वं सत् रात्र्यन्तरितं च यत् , उच्छिष्टमपि भुक्तशिष्टम् उच्छिष्टम् , अमेध्यम् अयज्ञार्हम् , भोजनम् ईदृशं तामसप्रियम् ॥ १० ॥
In plain words
'Yatayama' means half-cooked, undercooked -- since the loss of real vitality is already covered by the next word, 'gatarasa.' 'Gatarasa' means the taste has simply gone out of it. 'Puti' means it has gone rank, foul-smelling. 'Paryusita' means it was cooked and then left sitting overnight. 'Ucchista' means it is someone's leftovers, what remains after eating. 'Amedhya' means it is not fit to be offered at all. Food like that -- that is what a tamasic person actually wants.
Close to the Sanskrit
'Yatayama' [means] half-cooked, because [the state of] lacking vital potency is already expressed by the word 'gatarasa.' 'Gatarasa' [means] devoid of taste; 'puti' [means] foul-smelling; and 'paryusita' [means] having been cooked and left overnight; 'ucchista' too [means] leftover, [i.e.] the remainder of what has been eaten; 'amedhya' [means] unfit for sacrifice; food of this kind is dear to the tamasic [person].