Because of its very porous nature, charcoal has the particularly high ratio of surface area to weight required of an absorptive material. In winemaking it is used mainly to absorb the colloidal pigment polymers responsible for amber or brown colours in white wines, particularly in the manufacture of Pale Cream sherry. Off-flavours in wine are occasionally removed using a grade of active charcoal with a smaller pore size, transforming an unsaleable wine into a neutral one for use in a basic blend. Charcoal is also used on juice to remove off flavours caused by botrytis or sour rot, for example (a process known as Kohlschönung in Germany, where the practice is relatively common). However, this may have a negative effect on the quality of the wine.