Reference for Avodah Zarah 131:2

אביי אמר במשהו בתר טעמא אזלינן אידי ואידי חד טעמא הוא דהוה ליה מין במינו ומין במינו במשהו

Abaye said that [they are prohibited] however small the quantity. For we use the criterion of flavor, and since both [the wine and grapes] have the same flavor, it is a case of one species being mixed with the same species, and in such circumstances the mixture is prohibited even if there is the smallest quantity.

Jastrow

Jastrow