3
In the Beginning There Was an Egg
How would our culinary universe look if we did not have the egg? No boiled, fried, poached or scrambled. No omelets. How would you make an angel cake or muffin if you didn’t have an egg? We would live in a cake-less world. Not even pancakes. Just think about all the pancakes in the world—they would all be non-existing without eggs. How would you make sauces such as mayonnaise, Hollandaise or sabayons without eggs? Custard for your pies, or delicate meringue desserts such as pavlovas or baked Alaskas? Indeed, egg is a cornerstone of our gastronomy without which the most important foams, gels, and emulsions would be practically impossible to make. Or would they really?
Meringue from egg white or pea? The fact that you can make a perfect meringue completely without egg whites is not an invention that should be credited to any chemist. On the contrary, chemists have kept on telling the story about the wonderful proteins of egg whites—how the different types of molecules cooperate to decrease the surface tension of water, increase its viscosity, and finally gently denature onto the surface of air bubbles to form a thick and elastic film to produce airy, strong and long-lasting foams. This foamy structure is in turn used for culinary purposes in many dishes such as souffles and airy cakes. And yet, suddenly in the early 2000s recipes started appearing in vegetarian and vegan cooking magazines, web pages, and blogs claiming that there is a vegan ingredient with the same properties! And this has triggered an avalanche of new vegan recipes for meringues, angel cakes and other light and airy delicacies. On top of this, their advice was extremely simple: just replace the egg white in your recipe with the liquid from your canned chickpeas and proceed as usual. For example, a meringue recipe would look like this:
Meringue
Ingredients
1.5 dl chickpea liquid (or equal amount egg whites)
1.5 dl fine sugar
1 teaspoon lemon juice
1 teaspoon vanilla sugar
Procedure
1. Pour off and strain the liquid from one package cooked chickpeas, or separate egg whites from the yolks. Add the lemon juice and whisk it into a soft foam.
2. Add the other ingredients and continue whisking at full speed for 5 minutes or until the foam stands up in stiff peaks.
3. Transfer with a spoon or piping bag onto a lined baking tray.
4. Bake the meringues in the oven at 100°C for 1 hour 40 minutes.
5. Turn the heat off and leave the meringues in the oven until cooled (1–2 hours).
The vegan and vegetarian food writers praised the chickpea meringue, but none of their reports compared chickpea liquid and egg white in a systematic way, so naturally we were somewhat skeptical. We had to see this with our own scientific eyes: had the egg white met its equal in the world of foaming agents?
A little egg white chemistry. Egg white contains a number of different proteins amounting to approximately 10% of the white, the rest being practically only water. Together these proteins are able to turn the watery egg white into an airy and stable foam—if only someone gives the water solution a good whisk.
Turning a water solution into a foam requires an ingredient with various, specific properties. First, the surface tension of the water must be lowered so that the water molecules clinging together due to weak molecular forces are more readily separated and thus can surround the air bubbles introduced by the whisking.
Secondly, the viscosity of the water solution must be increased so that the very thin layers around the bubbles are not easily drained off due to the force of gravity. If the solution is too thin, the liquid quickly ends up in a puddle at the bottom of the bowl—the foam becomes weak and brittle and will easily collapse. The various types of proteins take on different roles in this process.
Some of the long protein threads, initially tightly bundled together, denature and get entangled in each other to produce a web that encloses the bubbles. Other proteins remain intact and act as lubricants between the layers of webs. Together they form a film around each bubble that is strong and elastic at the same time (“viscoelastic”). Egg white proteins are surely team players even though they do not have any consciousness about this themselves.
Protein |
% |
Denaturation temperature/°C |
Role in foaming |
|---|---|---|---|
Ovalbumin |
54 |
84,5 |
Denatures during whisking |
Conalbumin/ovotransferrin |
12 |
61,5 |
Does not denature during whisking |
Ovomucoid |
11 |
70 |
Strong structure, does not denature during whisking |
Ovoglobulins |
8 |
92,5 |
Lowers surface tension, increases viscosity |
Lysozyme |
3,4 |
75 |
Lowers surface tension, increases viscosity |
Ovomucin |
3,5 |
70 |
Forms denatured film on surface of bubbles |
Other proteins |
Ca. 8 |
^Various proteins, various roles. Source: Belitz, Grosch and Schieberle (2009).
The powerful foam of chickpea liquid. We wanted to study if the rumor was true—could the chickpeas’ foaming capacity compete with that of egg whites? We bought three boxes of cooked chickpeas (unsalted, organic) and randomly took three eggs from the fridge. The latter move would later show itself as a mistake. We will return to that issue later. The workshop attendants were divided into two groups: the foam group and the meringue group. Both groups were given two KitchenAid machines, identical sets of other necessary kitchen utensils and instruction for the speed setting for the KitchenAid machine. The first group was asked to report on the time it took to produce a foam, foam volumes right after whisking and how long it took for the foam to start to leak liquid. The second group was asked to compare the two foams in with respect to aroma, taste, and texture.
The first group noted that the egg white at 12.5 minutes was somewhat quicker to form a foam compared with the chickpea liquid at 13.5 minutes. But the chickpea juice gave a slightly higher volume (2.7 dl vs. 2.2 dl for the egg white), and the former gave a far more stable foam than the egg white. Indeed, while the egg white foam started leaking after only 5 minutes, the chickpea foam only started leaking after 15 minutes. So that evening we learned that chickpea juice can indeed be a very potential foaming agent! Making foam was just as easy for both; chickpeas produced more foam for the same amount of liquid, and it was even more stable.
But the weakness of our egg white foam made us suspicious of the quality of our eggs, so we measured the pH of the whites with a pH indicator paper. Our suspicion was confirmed: a pH of 9.5! In fresh eggs, the pH of the white is commonly around 6, from where it rises as the egg ages. What an embarrassing mistake! While attempting to adhere to the scientific principle of picking eggs randomly we had picked old ones! Such a high pH indicates that the eggs are really quite old and will therefore have lowered foaming properties and poor water-holding capacity. So, this comparison was probably quite unfair on behalf of the egg white. But still, we had shown that chickpeas are a potent competitor, and at least in a battle with old eggs, chickpea juice was the winner.
During storage, carbon dioxide gradually seeps out through the egg shell. Dissolved in water, carbon dioxide is in the form of the weak acid carbonic acid. As long as the carbonic acid is present, the pH in the egg is kept in check, close to neutral. But as the carbon dioxide evaporates, the pH starts to rise and can finally reach values as high as 9.5—alkaline indeed, and a clear sign of mature age. Aging also breaks down the proteins responsible for producing and stabilizing foam. The egg white solution also is less viscous due to the gradual breakdown of the long protein molecules. The result is egg whites that are difficult to whisk to a foam, a foam that collapses more easily and a liquid that is more easily drained off the bubbles due to gravity drains, ultimately giving a dry and brittle foam with a puddle of watery liquid at the bottom of the bowl. ×
The second group who tasted the two (uncooked) meringues noted that they had very similar flavor and texture properties, indeed. There were some differences, however. The egg white version appeared to be shinier and the foam denser and smoother than the chickpea version. The mouthfeel of the chickpea version was claimed to be thinner and it also melted quicker in the mouth. The taste of the chickpea version was somewhat sweeter and the aroma also differed slightly in the two versions. There was a noticeable beany flavor in the chickpea meringue. But this was surprisingly weak, and the group speculated that it might fade away during cooking. The citrus flavor was somewhat more present in the egg meringue, while the chickpea version had a slightly more pronounced sweetness. All in all, the egg white version seemed to get a slightly more favorable evaluation, but with a narrow margin. The tasting was not a blind tasting so we cannot disregard possible preconceptions among those who tasted the two sweet foams to have affected the result. Considering that most of the panelists prior to the test had indicated their doubts about the power of the chickpea, this meringue came out very favorable. On top of this, the beany flavor of a chickpea meringue might be suppressed when the meringues are baked, so we might even have done the chickpeas some injustice.
In 2013, food scientist Johanna Söderberg submitted her PhD thesis at the Swedish University of Agricultural Sciences about foaming, emulsifying and gel forming properties of legume-derived proteins, as alternatives to those derived from eggs. Indeed, it seems that one can make vegan, foamy delicacies such as meringue, or emulsions such as mayonnaise, by replacing egg with soybean or pea proteins as long as they can be dissolved in water. Canned peas and beans are normally made by cooking them at approximately 120°C under high pressure. During this process, proteins, and possibly also other foaming agents such as carbohydrates, are dissolved in the cooking liquid, which thereby turns into an excellent foaming agent. It is not only chickpeas that contain significant amounts of proteins with similar properties to those in eggs. Various blogs and other open sources give long lists of ingredients suitable for this purpose: white beans, red beans, lentils, soybeans, gluten, rice, hemp, and quinoa. This is surely an invitation to start experimenting! In the future, we should expect to be offered foods in which egg or other animal proteins are partly or wholly replaced by what many of us thought should be discarded, but recently has received its own name as a functional ingredient: “aquafaba.” Literally meaning bean water (aqua = water, faba = beans), the word received its place in the Oxford English Dictionary in 2016. Johanna Söderberg’s results indicate that we probably have to accept a mild beany flavor if we want to use these vegan alternatives. But she also observed that as much as 25% of the egg proteins could be replaced by their legume-derived counterparts without any noticeable effect on flavor or texture.
Even though food scientists studied legume constituents for decades, apparently few had thought that the world of vegetables had an ingredient that could compete with egg whites as the basic structure for foams in our home cooking. But then some food writers showed us that it is no big deal to make wonderful vegan foams. Actually, we are more than happy to have been shown up. Indeed, everyone deserves to be able to enjoy the fluffy happiness of meringues, soufflés and other airy delicacies! And surely, science will follow with research to back up the experiments of bloggers, chefs, and others, be it professionals or amateurs, sharing their experience with the rest of us.