In my view, 18°C is the perfect temperature for enjoying all the qualities of a red wine. Colder, and the tannins appear hard and firm up to the point of becoming harsh. Warmer, and the wine gets flabby, loses its fruitiness and the taste of alcohol becomes dominant.
The temperature can be a little higher or lower by perhaps one or two degrees.
A gentle, prolonged exchange of oxygen allows the aromas to fully express themselves: aromatic intensity and complexity are at their peak.
The tannins also appear more velvety and silky on the palate.
Generally when the wine is aerated, it also warms up and the two factors combine.