Crust is the name for sediment that forms in a bottle aged port.
The presence of the crust is the result of the natural wine making process. It indicates the wine has continued to improve in bottle, developing aroma and character with age.
Crusted port, a style rarely seen these days, is a blend of vintage ports that would be released and ready to drink sooner than a vintage port and at much more attractive price.
The ‘crust’ or sediment in the bottle means you should decant before serving.