Questions & Answers - What is Castor/Caster Sugar
What is castor sugar? - Joanne Brewer (11/8/01}
Answers:Castor/caster sugar - Spelled both "caster" and "castor." The spelling castor sugar used to be the prevailing one, but caster sugar seems to be more usual now, perhaps because it is used by some sugar manufacturers on their packaging.
UK castor/caster sugar is very finely granulated sugar (finer than U.S. granulated sugar) which allows it to dissolve almost instantly. In the United States, superfine sugar or Baker's sugar may be substituted.
called "berry sugar" in British Columbia.