EUNOSTOS (or Eunostus) was the goddess of the flour mill. It is unclear whether the names Eunostos and Promylaia refer to a distinct goddess or if they are simply titles of the goddess Demeter.
EUNOSTUS (Eunostos). A goddess of mills, whose image was set up in mills, and who was believed to keep watch over the just weight of flour. (Hesych. s. v.; Eustath. ad Hom. pp. 214, 1383.)
Source: Dictionary of Greek and Roman Biography and Mythology.
Suidas s.v. Nostos (trans. Suda On Line) (Byzantine Greek lexicon C10th A.D.) :
"Nostos: In common use ‘sweetening’, in the case of foods . . . But from nostos in the customary usage comes nostimon, ‘pleasant’, and Eunostos, a certain god, they say, of milling."
Suidas s.v. Promylaia :
"Promylaia: A goddess presiding over milling, whom they worshipped in mills, like Eunostos."
- Suidas - Byzantine Greek Lexicon C10th A.D.
Other references not currently quoted here: EUNOSTOS Hesychius s.v. Eunostus, Eustathius 214.18 & 1283.42;
PROMYLAIA Pollux 1.180