There are many varieties of sugar and despite their similarities they aren't all interchangeable. Here's a quick guide to the most common types of sugar.

Common Sugar

This is your everyday white table sugar. It has a large variety of uses, which we won't go into in this guide for the sake of brevity! Normal granulated sugar has a grain size of about 0.5mm across. You can also get larger grained sugars such as hail sugar which is popular for decorating cookies and other deserts.

Caster Sugar

Caster sugar is preferred in pastry and cake making as the granules are finer (around 0.35mm) and dissolve faster. With more sharp edges to cut through fat, batters become aerated more rapidly. Caster sugar also dissolves into beaten eggs for meringue with greater efficiency, and it's worthwhile to know that table sugar will typically produce a cake with a speckled crust.

A small note on etymology, the term caster or castor sugar is a British term given to sugar fine enough to fit through a sugar "caster" or sprinkler. In the United States this sugar is also sold as "superfine" sugar.

Icing Sugar (or confectioners sugar)

This is crushed, powdered granulated sugar. It is used in icings, fillings and some pastries, such as friandes and sable. It's also one of the most important ingredients in cake decorating. This is because icing sugar is the basis of royal icing, which is used for decorating and writing, and it's also used to make "cake glue" and to dust surfaces before rolling out icings.

There are a few different sorts of icing sugar and they are not interchangeable. Pure Icing Sugar is pure unmixed sugar with no additives. Pure icing sugar is quite lumpy and usually needs to be sifted. This is the sugar used for Royal icing. Icing Sugar Mixture is sugar that has been blended with a small amount of cornflour (around 4%). It's not so good for cake decorating work as the small amounts of flour present can start to form mould if there is any moisture in the cake or decorated items (and there usually is). Pure sugar will not mould. Icing sugar mixture however is fantastic for making simple glazes and icings, and fillings where a small amount of cornflour will not effect the result. It does not clump or lump and this is a definite advantage. Snow Sugar is icing sugar with a mixture of cornflour and a touch of vegetable fat and dextrose. This mixture produces a sugar that doesn't melt when dusted onto cakes and tarts. This is its primary use, although I have spoken to customers who bake with it very successfully.

Palm Sugar

Comes from a sugar-giving tree of which there are several. The most generous is the Asian sugar palm. The sap is collected from the flowers or from a tap in the trunk then boiled down to syrup (called palm honey) or crystallized to a mass. The dark sugar is often called jaggery and has a distinct almost winey aroma. It is mostly used in Indian, Indonesian and some African cuisines. A lighter palm sugar is also used extensively in Thai cuisine. This lighter palm sugar is the most common palm sugar used in our kitchens in Australia.

Brown Sugar

Brown sugars are softer and moister than granulated sugars. Their crystals are coated with a molasses like syrup. Darker sugars are more intensely flavoured, as the colour relates to the molasses retention. Glucose and fructose are present in the molasses syrup coating the crystals. These attract and retain more moisture in the sugar itself, making brown sugars great for baking, as the products will retain more moisture and stay fresher for longer periods. Granulated sugars are 99% sucrose and brown sugars vary between 85-92% sucrose along with glucose and fructose. If brown sugar is used instead of granulated sugar the result will be more flavourful and moist but the browning temperature will be lower. Demerara sugar can also be in this category, as it often comes from the first crystallization of cane juice, producing yellow gold crystals that are frequently washed with alcohol to make them shiny and clear. Muscavado sugars are the crystallization of the dark mother syrup forming very small sticky intensely flavoured sugars.

Invert Sugar

Invert sugar is made from a sucrose water solution (basic sugar syrup) that is heated with the addition of acid. Although invert sugar naturally occurrs in honey, molasses and corn syrup, to name a few, it can also be purchased as a paste or syrup. It doesn't crystallize and it retains moisture. It is sweeter than sucrose (standard sugar), and when added to baked goods it will keep them moist longer. It also helps prevent ice formation in ice creams and sorbets. Therefore, it is used extensively in ice cream, sorbet, glazes and sauces, fondant and candy making. Fudge and caramel sauce are two examples where a non-grainy texture is important.

To make invert sugar, simply boil 3 parts sugar with 1 part water (by weight) and add an acid. For example, add 3kg sugar to 1litre (or kg) water and approx 3-5g of citric acid. Bring this to the boil, strain and cool.