This article is from the Cooking and Conversions FAQ, by with numerous contributions by Victor Sack cooking.faq@mac.com others.
UK castor/caster sugar is somewhat finer than US granulated sugar.
There is a product in the US called superfine sugar, which is about the
same as UK castor/caster sugar. It is called "berry sugar" in British
Columbia. Usually, you can use granulated sugar in recipes calling for
castor/caster sugar and vice versa, but I've got reports of times this
didn't work so well! As usual, give the recipe a trial run with the
substitute some time when it doesn't need to be perfect.
(US) Confectioner's sugar is (UK/Aust/NZ) icing sugar. Sometimes these
are marketed as mixtures containing about 5% cornflour (cornstarch).
This can interfere use in making candy such as marzipan.
Corn syrup is common in the US but not always elsewhere. Sugar (golden)
syrup can be substituted.
Corn syrup comes in two flavours - dark and light. Light corn syrup is
just sweet, dark has a mild molasses flavour. Some people have
substituted dark corn syrup for golden syrup in ANZAC biscuits and found
it successful. A common US brand is Karo.
Golden syrup is a thick, golden brown (fancy that) by-product of cane
sugar refining. The taste is mostly sweet, although there is a slight
acidic, metallic component. Lyle's is a common brand spoken about in
rec.food.cooking, the New Zealand brand name is Chelsea.
If desperate, a plain sugar syrup may be a possible substitute, boil 2
parts sugar, 1 part water. This could be messy. You may want to thin
it out with water. Again, you may want to try this out on your own
before making something for a special occasion.
Black treacle and blackstrap molasses are similar but not identical.
 
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