Hilchos Issurei Mizbeiach 7:6

Libation wine was brought from grapes that grew at the foot of vineyards that were worked twice a year. The grapes were tread and the juice collected in small jugs. These were not stored alone or in pairs, but in groups of three. The jugs weren’t filled to the top so that the wine’s aroma should be detectable. Libation wine wasn’t brought from the mouth of the jug, because of the flour-like residue that rises to the surface, nor from the bottom, because of the dregs. Rather, it was taken from the middle of the middle third.

Hilchos Issurei Mizbeiach 7:7

The Temple treasurer would sit while the wine flowed from a hole in the side of the jug. If he saw dregs starting to come out, he would stop and not buy it. Wine was brought from after forty days from pressing until two years, or a little more. If one brought wine that is even older, it is fit so long as it hasn’t turned.