Icing of Biscuits

A small but significant number of biscuit products are half coated with icing. This adds visual appeal, particularly for children, and being dry and hard does not become messy when handled or in warm weather.

Icing is applied to the biscuit as a thick aqueous suspension. It is usually coloured and may be flavoured, although this is usually very mild. After application the coating is dried. The result is a hard glossy finish which greatly enhances the appearance if not also the eating qualities of the biscuit.

Methods of apply icing

The drying process is slow so it is unusual to have biscuit icing as an in-line secondary process. A drying tunnel would have to be very long to accommodate even a short biscuit oven. The exception is where the amount of icing applied is very small. In these cases icing can be applied immediately after baking while the biscuits are still hot and the heat from the cooling biscuits will be enough to dry the icing.

Normally biscuits to be half coated or "iced" are magazine fed. Typically a flat icing is applied as a fluid coating on the underside of the biscuit only, like half coated chocolate biscuits, or it is stencilled on in a more or less distinct shape. In other cases icing is applied only on the raised parts on the top of biscuits, to highlight the patterns. If an aerated icing mixture is used it is possible to pipe (deposit) the icing in which case deposits with high relief can be produced.

Many other techniques have been used such as contact icing (where a coated roller deposits only on the points of the biscuit that it touches), wire cut deposits by using modified sandwich creaming machines, spraying to producing more of a glaze than an icing and screen printing. These systems are rather specialised and have usually been developed by innovative plant engineers in individual factories.

Our principle concern here is with the normal icing technique, usually of a short dough biscuits.

The most usual method of coating biscuits with flat icing is with an arrangement very similar to a chocolate enrober for half coating. Biscuits are fed onto an open wire mesh conveyor or onto a system of fine ropes of nylon or cotton which is drawn through a bed of icing mixture so that the base and edges of the biscuit are coated. The biscuits are then turned over as they leave the icing machine so that the icing may be dried.

If a stencilling arrangement is used, similar to that described for biscuit creams, it is not necessary to invert the biscuits after application of the icing and it is also possible to apply more than one colour at once in the form of stripes. These coatings then may be further decorated with fine lines of icing trickled over the surface or drawn into simple patterns with reciprocated wire fingers.

All flat icings are rather fluid and sticky so care is needed to make sure that the biscuit conveyors do not become soiled resulting in patches of icing adhering in the wrong places.

A double icing technique, where a flat coat is dried and then a further deposit is stencilled on in a fine pattern, allows the production of intricate designs of animals, flowers, letters, words or even company insignia. However, it will be appreciated that as this involves a double drying operation, the whole production process is rather long.

There are not many biscuits with piped icing deposits but Iced Gems (very small round hard sweet biscuits with a large deposit of icing in various colours) is a well known traditional variety which is very popular with children. Because the biscuits are small and relatively light they must be held down, usually by air suction, after they have been rowed up for presentation to the icing deposit nozzles. Several different colours are deposited at once so that the biscuits, after drying, can be collected together en masse and jumble packed as a variety.

Composition of the icing

The icing is simply a suspension of very fine icing sugar in water with some gelling material, such as gelatin, pectin or egg albumen, to give it some "body" and increased viscosity. For flat icings gelatin is normally used. The gelatin should be used at about 1% of the sugar weight, but the quantity is related to the water needed to give the icing the correct viscosity for the machine used for coating or depositing. Low bloom strength gelatin gives icing that is more tolerant to processing variables.

Drying of the icing

Biscuits are very hygroscopic and uptake of moisture softens them (the major cause of staling) and causes them to expand. When a water based material is added, as when they are iced, it is essential that drying proceeds without delay so that moisture penetration is minimal and dimensional changes do not cause cracking in the icing at the later stages in drying.