Whether using a bundle of twigs or an electric beater, knowing the science can help when making an egg white foam.

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History remembers the big ideas and the big thinkers. The Einsteins, the Newtons and the Confuciuses.

In every age, though, there were thousands of innovators that went unrecognised. Normally these people were in occupations not thought worthy of record. Or they were women.

Until recently cooking was one of these fields of human endeavour that simmered below the surface of history. We eat everyday but the history of food was not usually deemed worthy of scholarly attention.

It’s difficult for us living in the modern world to grasp this concept. In our world boiling a zucchini gets you 360,000 likes on TikTok.

But, the fact is, we don’t know how many of our favourite foods and modern techniques were developed. New dishes just seem to appear in the historical record, not quite fully formed perhaps, but pretty close.

Using egg whites to create a stabilised foam is one of these culinary techniques that seemed to just pop into existence.

Sometime in the late 1600s, chefs worked out that prolonged whisking of egg whites produced a relatively stable foam that could be used to make things like souffles, meringues and mousses.

Why this happened in the late 1600s we aren’t too sure.

The key innovation seems to have been the use of bundles of straw as a whisk but we’ve had twigs for a long time. Why didn’t someone catch on sooner?

Who knows? Maybe it was just the spirit of experimentation that infused the times. But happen it did and now we have souffles, mousses, meringues, macarons, pavlovas and many other dishes that rely on the unique chemistry of egg whites that enables them to create foams.

Scappi, the original celebrity chef

The exception to people not writing cooking lore down is the 1000 page illustrated cookbook published by Bartolomeo Scappi in 1570. This was the first illustrated cookbook ever published and it was a runaway success.

Scappi was way ahead of his time. Not only in publishing a cookbook. You could also say he invented fusion cooking. Combining, as he did, different culinary traditions into elaborate dishes.

It wasn’t until the 18th century that other chefs caught up and started thinking about their business in the same way Scappi did. And our knowledge of culinary history is all the poorer for it.

If you want to read more there is a good article here.

Why Water Needs Proteins or Fats to Form a Stable Foam

If you agitate some some water, shake it or whisk it, you can briefly see bubbles of air appear in the water but they quickly rise to the top and escape into the air.

This is because water has a high surface tension. Water wants to interact with water so air is quickly excluded.

If you want to create a foam you need something to prevent the air from interacting directly with the water, like oil and water in an emulsion, but you also need structure to trap the air bubbles in the liquid and allow the foam to maintain its shape.

We’ve actually already looked at one foam, whipped cream, where partially disrupted milk globules interact with air and each other to build structure around air bubbles, trapping them and stiffening the foam.

Turns out you can do a very similar thing with egg whites. In this case, instead of milk fat, you are using egg proteins to build structure in the watery matrix of the egg white.

Egg Proteins and Foam Formation

It may seem odd but whisking an egg is quite similar to frying it. If you read my post on frying an egg, you’d know that when you heat an egg proteins unravel and form a network of interacting proteins (a process called denaturation by protein chemists).

The same process occurs when we whisk egg whites but, instead of heat, it is the physical abuse of the proteins that causes them to denature.

When they unfold proteins expose their hydrophobic (water fearing) core. Much like the fats in cream, which are also hydrophobic, the hydrophobic parts of the protein prefer interacting with air and they start trapping the air that the whisk is forcing into the mixture.

The unfolded proteins also start interacting with each other. Gradually, a cross-linked protein network forms with the hydrophobic parts of the protein interacting with air and the hydrophilic parts (the water loving parts) interacting with water.

This protein network is the scaffold that stabilises the air bubbles, provides structure and thickens the foam.

Controlling the Stiffness of Your Foam

The longer the whites are whisked the more extensive the protein network becomes, the more water is trapped and the firmer the foam becomes.

This gradual build up of structure allows us to control just how stiff we want our foam.

At the soft peak stage there is still ample water that hasn’t been captured by the growing protein network which provides lubrication for stabilised air bubbles to slide past each other.

As whisking continues the increased structure captures more and more of the free water. By the stiff peak stage most of the water has been captured and the air bubbles are held in place by the now extensive protein network.

There is also no water between the foam and the bowl meaning the protein network can cling to the bowl, leading to the famous test for stiff peaks; holding the bowl containing the foam upside down over your head.

Which stage you want to get your foam to is a function of what you are going to use it for.

The stiffer the foam the harder it is to incorporate into something else so for things like souffles and mousses you probably want a softer foam while something like a meringue, which is normally an element in and of itself, you probably want a much stiffer foam with plenty of structure.

The Chemistry of Over-Whipping (and Why Copper Bowls Work)

One of the dangers of wanting a stiff foam is that you can over-whip your egg whites.

When this happens the protein network tightens so much that it starts to squeeze out water and the foam splits and becomes grainy with coagulated protein.

There aren’t many uses for over-whisked egg whites but adding another egg white and gently whisking might re-emulsify the mixture and rescue your foam.

Copper Bowls can Help Stop Over-Whipping

You can make it harder to over-whip your egg whites, though, by taking advantage of an old French tradition of using copper bowls.

It may seem a little fantastic but copper bowls can prevent over-whipping because of the role cysteine amino acids play in protein interactions (amino acids are the building blocks of proteins).

Cysteines are amino acids that have a side chain that is terminated by a sulphur bound to a hydrogen atom (-SH). Cysteine is a weak acid so, in water, it is often without the hydrogen atom.

When this happens the free sulphur atom can form what is known as a disulphide bond with another cysteine residue on another protein. This cross-links the two proteins together.

Copper atoms bind tightly to free sulphur atoms. So in a copper bowl, tiny amounts of copper end up bound to cysteine residues in the proteins of the egg white.

This blocks the formation of disulphide bonds and effectively removes one of the ways that the proteins can interact. Without these bonds it is more difficult to over-whip egg whites because the proteins cannot form the very tight network that causes the foam to split.

Adding small amounts of copper powder to the whites also works as do silver bowls, if you can afford it.

Acid Can Also Prevent Over-Whipping

Acid will also help prevent you over-whipping your egg whites. Because cysteine is a weak acid if there are a lot of hydrogen ions floating around then it becomes harder for the sulphur to lose its hydrogen.

Acidity is really just a measure of the amount of hydrogen ions in a solution and a low pH means there are a large number of them floating around.

In these conditions the sulphurs on the cysteine residues will not be able to lose their hydrogen ions and wont be able to form disulphide bonds.

How much acid? Harold McGee recommends adding 2ml lemon juice per egg white to the mix before starting to whisk.

Things That Make it Harder to Form a Foam

Some things can make it harder to form a foam from egg whites. If you are whisking by hand, this is not something you want to put yourself through.

Salt Stops Protein Interactions

Salt is one thing that will maker it harder to form a foam. The constituents of salt, sodium ions (Na⁺) and chloride ions (Cl^–), interact with the charged or polar parts of a protein that would otherwise be interacting with other proteins (via hydrogen or ionic bonds).

Removing these protein interactions makes it very hard to form the protein scaffold and so a stable foam.

Sugar Slows Protein Denaturation and Increases the Viscosity of Water

Sugar also makes it harder to form a foam, which can be a problem when making meringue, a sweetened egg white foam.

Sugar slows the denaturation of the proteins and so slows the formation of the protein network.

This isn’t a problem if you have an electric mixer, or you want some exercise manually whisking, but it also makes for a heavier, fine grained foam because sugar also increases the viscosity of water making it harder for it to spread out into walls around the air bubbles.

Once a foam has formed though sugar can act as a stabiliser. Because of the increased viscosity it reduces the amount of water that leaks from the foam over time.

If you cook the foam, which you often do with meringues, sugar will also add more structure because it forms solid dry strands of sugar, which also makes the meringue crispier.

For these reasons, when making a meringue, sugar is usually added after some structure has formed, though a heavier, sugar at the start, meringue is sometimes used.

Ingredient / Condition	Effect on Egg White Foam	Scientific Reason	Best Timing / Practice
Copper / Silver Bowl	Prevents over-whipping	Metal ions block disulfide cross-linking	Use during the entire whipping process
Acid (Lemon Juice / Cream of Tartar)	Stabilises foam, prevents splitting	Increases hydrogen ions, preventing excessive protein bonding	Add 2 mL per egg white before whipping
Sugar	Stabilises foam & retains moisture	Increases viscosity and forms solid sugar strands when baked	Add gradually after soft peaks form
Salt	Weakens foam stability	Inhibits ionic/hydrogen bonds needed for protein scaffolding	Avoid or add to dry ingredients later
Fats / Egg Yolks	Destroys foam	Competes for space at the air-water interface without providing structure	Keep whites 100% pure and free of oil/yolks

Foam Killers: Why Fats and Egg Yolks Ruin Meringue

A golden rule in whipping eggs is keep anything that is happy at the air-water interface out of the mix.

In the emulsions post we saw that something like a fatty acid will have it’s hydrophobic part toward the air and it’s hydrophilic part in the water.

The problem when trying to build a foam is that any emulsifiers present at the air-water interface won’t cross-link with the proteins and won’t provide any structure.

This makes it much harder to achieve a stable foam and if you have too many of these molecules you wont be able to form a foam at all.

Oils and fats, although they aren’t emulsifiers, will also want to congregate at the water-air interface precluding proteins and preventing the formation of structure around the air bubble.

They will also interact with the exposed hydrophobic cores of the denatured protein stopping them from interacting with each other.

We know that egg yolks are not only packed with fats (triglycerides and cholesterol) but they are also packed with emulsifiers both of which will congregate at the air/water interface.

This makes egg yolk fatal for the formation of a foam from the egg whites. The yolks are also the most likely contaminant so be careful when separating your whites from your yolks if you plan on making a foam.

Conclusion

Understanding how to form a foam from egg whites is one of those things that opens up a whole vista of potential dishes.

Things like meringues, souffles and mousses all rely on the extra structure and airiness that the incorporation of an egg white foam brings. There is more science to these dishes, of course, but I’ll cover them in future posts.

Hopefully what we’ve covered here can help when you are making an egg white foam. Especially if you are using a bunch of twigs as a whisk.