The obvious place to start is with the ingredient which makes up the body of the drink. Red wine is essentially one big, pleasant cocktail of chemicals – like all alcoholic drinks, it contains ethanol, but it also contains a range of other organic compounds which influence its taste and colour. A class of chemicals called anthocyanins provide some of the colour, and can also interact with other chemicals in wine called flavonols to influence the wine’s hue. Some bitterness comes from another chemical group, the flavan-3-ols, whilst much larger organic molecules, known as tannins, impart astringency. There’s much more detail on the chemistry of red wine in this previous post on the site.