Technical Talk: November 2006

When the Icing Takes the Cake

Question: How do icings work, and how can I use them on baked goods without problems?

Answer: There many varieties of icings used by bakers and confectioners to enhance the appearance and taste of their products. In general, icings are characterized according to their fat content.  Flat icings contain no fat and are normally used on sweet-dough, baked goods. Icings that contain 3 to 5 per cent fat are classified as cupcake icings. A third category — cake and cream icings — contain anywhere from 10 to 25 per cent fat.

Icings are combined sugar and water systems that have a certain balance between the dissolved (liquid form) and suspended sugar crystals in the system. This balance is held in place by the addition of various ingredients such as hydrocolloids and other stabilizing components. These ingredients work in a way that will modify sugar’s ability to dissolve or re-crystallize in a water system. There are various characteristics of an icing that collectively, if achieved, result in stable icings. Such characteristics include good aerated cellular structure, the smoothness of the icing, the ability to maintain its appearance, and the ability to resist runniness, which results from liquid separation. Other characteristics include good spreading and handling under normal temperature conditions, adherence to the baked goods, and reduced run-off. Stable icings under their normal storage have the ability to retain a constant amount of moisture without losing or absorbing water from their surrounding storage environment. Thus, a stable icing will maintain its structure, glossy appearance, and colour, and will not become gritty during normal shelf life.
In order to achieve these characteristics, various gums and other ingredients are used to improve gelling, suspension, emulsifying, and film forming for the icing system.

The type of sugar used in the different types of icings varies according to the desired characteristics. The most common sugar used is sucrose.  Dextrose, corn syrup or invert sugars are used in very low levels when a glossy appearance to the finished product is desired. These sweeteners have high humectant properties, or the ability to absorb water from their surroundings — forming a thin film of syrup on the surface, giving a shiny glossy appearance.

Another important ingredient used in icings is fat or shortening.  The amount of fat used depends on the type of the icing ranging from 0 to 25 per cent.  Other ingredients may contribute to the fat content of the icing. For example, when chocolate is used, the fat content of the chocolate should be taken into consideration.  For the same reason, when butter is used, the flavour contribution to the overall taste should be taken into account, and the salt content should be included in the total calculation of the formula. In some cases, fully hydrogenated shortenings with high melting points are used in small amounts in order to speed up the drying and help stabilize the icings at room temperature. When you require the reduction of the consistency of an icing that contains fat, you should use simple syrup containing higher amounts of sugar than water in order to avoid further dissolving the sugar in the icing.  The consistency of an icing can also be reduced by simply raising its temperature.

Water is a very important ingredient in icings. It serves as the solvent medium for the sugar. In the process of making icings, the amount of water controls how much sugar is dissolved and how much remains in the crystal form.  It provides the desirable balance in stabilizing the icing at a given temperature of storage. The amount of water is so critical that very small increases can result in sufficient imbalance of the ratio of the syrup to undissolved sugar to cause weeping and melting. Another function of the water is helping hydrate other ingredients in the icing, such as gums and other stabilizing agents, enhancing their functionality. 
Eggs and milk are used as functional ingredients in icings as well. Eggs are used as whole, yolk or whites. Egg whites are used to assist the foaming and provide good volume and strength for the icing. They will also prevent bleeding and watering out.  Milk ingredients are recommended in the dry form in order to avoid the extra water.

Many types of icing stabilizers are available to assist in maintaining the desired shelf life. A stable icing will resist syneresis, sugar re-crystallization, moisture loss and hardening – allowing it to maintain its structure and consistency. The various stabilizers are available individually or in blends designed for the different types of icings. Special attention should be given to the selection of such ingredients when the icings will be subjected to freezing.

Many ingredients can be used in icings to perform different functions. Calcium sulfate and calcium carbonate are used for their buffering capacity to reduce shifts in pH. Mono- and di-glycerides are used as emulsifiers for various shortenings. Titanium oxide is also used as a whitening agent in some blends of icings.

Icings are complex systems that require a careful selection and blending of ingredients, as well as preparation procedures, in order to achieve the desired stable and appealing product.

For more information, or fee-for-service help with product or process development needs, please contact the GFTC at (519) 821 1246, by fax at (519) 836 1281, or by e-mail at gftc@gftc.ca.

This column is written by Dr. John Michaelides of the Guelph Food Technology Centre.