Glycerol (also known as glycerin and glycerine)
This viscous, colourless and odourless liquid gives the wine a softer, fuller more pleasant texture.
As there is a slight sweetness to glycerin, additional glycerine can be added to impart smoothness and reduce harshness.
Use it sparingly though, as a little goes a long way.
Add to taste, in increments of about 25ml per 5 gallons of wine.