What indicates that a glass is beer clean when beer is poured into it?

A beer-clean glass is crucial for presenting and enjoying beer to its fullest, and one of the key indicators of a beer-clean glass is the presence of proper head size and retention when beer is poured into it.

When beer is poured into a clean glass, it should form a suitable amount of foam, or head, which not only enhances the visual appeal but also contributes to the aroma and flavor of the beer. Good head retention indicates that the glass is free from oils, soap residues, or contaminants that could inhibit the formation and stability of the head. If the head dissipates quickly or fails to form properly, it can suggest that the glass is not adequately clean, which may affect the beer's overall taste experience.

The other scenarios listed fail to represent beer cleanliness: a greasy residue would likely prevent proper head formation, while cloudiness indicates unwanted particles or spoilage in the beer itself, both of which diminish the quality and enjoyment of the brew.