Eggs & Foams

Examining the stability of egg white foams A Foam is formed when gas is dispersed through a liquid. A very fine ‘honeycomb’ mesh is formed. Egg white foams easily. How does this actually work though?

Parts of an egg

How does egg foaming work? As liquid egg-white is whisked, the mechanical action causes its proteins to unfold and form a network, trapping air in tiny pockets. As the whisking continues, the air pockets become smaller. The change in colour (from translucent to brilliant white) is due to a trick of the light with the bubbles, rather than the egg's pigment. Essentially, the foam is composed of small gas bubbles dispersed through the egg-white. If the foam is left to stand, it will eventually collapse back into a liquid. But the physical change caused by whisking denatures the protein, depriving it of elasticity - it cannot be re-whisked successfully. If the foam is baked, protein coagulates and moisture is driven off, forming a solid foam commonly known as meringue

Which factors will effect the stability of an egg foam? The freshness of the egg white The temperature of the egg white The type of beater and shape and material of the bowl used The stage to which the egg white is beaten Any additions to the egg white What additions might we make to egg whites and why?

Which factors will effect the stability of an egg foam?

Old, cold, room temp or fresh eggs? In the white the proteins are tightly folded and tend to cluster. As it ages the egg - and especially the white becomes more alkaline. This causes the proteins in the white to repel each other rather than hold together- making the egg white runny. The proteins are still folded, but tend to be looser. When the egg whites are fresh, it takes more time and more force to whip those tight proteins into a foam. The foam that is created ends up more stable with small, strong, uniform bubbles. Cold temperatures also help keep the proteins rigid and stable.

Bowls and additions to egg whites Copper bowls were the favoured choice in the 1700. Copper ions from the bowl transfer to the egg foam and stabilise it. Plastic tends to have a bit of fat clinging to its porous surface, which can disrupt an egg white foam.. Cream of tartar is an acidic salt that can be used to weaken the elasticity of the egg white, allowing it to stretch more. This has the effect of stabilizing the foam, and is therefore an alternative to using a copper bowl. Sugar is added to sweeten the meringue and delays foam formation making it heavier but allows it to hold its’ shape better.

Types of meringue French meringue is made by gradually adding (usually caster) sugar to egg whites whisked to the soft peak stage. This mixture is then baked slowly to dry it out.

Types of meringue Italian meringue is made by melting the sugar into a syrup first and slowly dribbling this hot liquid into the whisked egg white. As the egg is cooked by the hot syrup – it’s often left like this for cake frosting etc without having a second bake

Types of meringue Swiss meringue is made by gently beating egg whites and sugar in a pan that sits above boiling water, without touching it. When the sugar is completely dissolved, the mixture is taken off the heat and beaten vigorously to increase and attain full volume and then at a lower speed until cool and very stiff. Swiss meringue is smoother, silkier, and somewhat denser than French meringue and is often used as a base for buttercream frostings

Getting egg yolk in the white When we make meringue only the egg white is used This foam is a protein-based foam, relying on protein ends hooking into each other. Even small traces of fat will prevent the foam from forming. Egg yolks contain high amounts of fat. Once an egg yolk breaks in your whites you have to start with a new egg because it can prevent your foam from forming.

Speed of whisk & length of whisking When egg white has been whisked for a long time the proteins become in effect ‘worn out’ When this happens - the foam collapses and ‘leaks’ liquid which is a process called synersis This can be affected by the speed of whisking and the length that the egg foam has been whisked

Different types of egg Whether it be chicken eggs, duck eggs or goose eggs – they all make meringue. However the water content of each egg will be different and this will affect the foam formation of the protein within. Lots of internet recipes say duck eggs make the best meringue. This may be because they contain more omega3 fatty acids and more acidic egg white leads to a more stable foam which is less likely to synersise.

Food colouring and Flavouring Many food colourings destroy egg foam – this may be because they tend to be oil based. Some gel food colourings work if they are painted on the inside of the piping bag. Flavourings (especially essences) are also mostly oil based, therefore freeze dried powders are usually used for flavour which are sprinkled on the surface. .

Taking a control sample Take a large and very clean mixing bowl, place 30g of egg white into the mixing bowl NOTE: it is important that the weight of each egg white stays the same- WHY? Using the hand held electric whisk and whisk attachments, beat the egg white until it’s at the stiff peak stage. Use the highest setting on the electric whisk. Record the time it takes you to reach the stiff peak stage. Transfer the beaten egg white into a measuring jug and record the volume of foam. Take a photograph too. Leave to stand for 5 minutes, then 30 minutes and up to 1 hour, if you have time. Measure the volume of foam each time and take a photograph. Also, observe whether any liquid has formed at the bottom of the measuring jug.