Green’s Dictionary of Slang

(US) muscatel, thus any cheap wine.

1968		Provincetown Rev. VII 85: Casks of t-bird, musky, even denatured alcohol [HDAS].
c.1972		C. Bukowski ‘The Copulating Mermaid of Venice, California’ 🌐 ‘Wait, wait, baby!’ screamed Tony. ‘What for?’ ‘The muscatel jug, asshole!’ [...] Tony was a man of his word. He came running out with the jug of muski.
1982		S. King Different Seasons (1995) 200: That fucking wino [...] was holding onto a twelve-cent bottle of musky.
2001		A. Pasanen Amer. Eng. Drinking Sl. 🌐 Cheap wine:red dog, muski (muscatel).