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Aquafaba & Other Hopes for Delicious Egg-free Meringues

Photo credit: veganbaking.net (vegan-baking/Flickr)

Photo credit: veganbaking.net (vegan-baking/Flickr)

Meringues are one of the few desserts that are simple yet elegant works of art. They are also precursors to other impressive, albeit considerably more complicated, desserts such as baked Alaska, lemon meringue pies, and macarons. At the bare minimum, all you need to make a fluffy meringue is egg whites, sugar, and an electric mixer—or an egg beater and some arm power. For vegans, this egg-containing dessert is not an option—but why should vegans (and those with egg allergies) miss out on this sweet, airy dollop of heaven?

To make a decent egg-free meringue, it helps to understand the meringue at the molecular level. How does a liquid get whipped into a cloud-like solid?

Egg whites, comprising 90% water, are undeniably runny. The other 10% consists of proteins, which play a major role in the fluid-to-fluff transformation. Mechanical stress from rigorously beating the egg whites causes the egg white proteins to denature, unfold from their natural structure. This exposes various amino acids, the building blocks of proteins, to the rapidly aerating environment. Some of the amino acids are hydrophobic (water-fearing), and some are hydrophilic (water-loving). As the egg whites are whipped, hydrogen bonds form between the hydrophilic amino acids and water in the egg whites. The hydrophobic amino acids prefer to be exposed to the air that is quickly beaten into the liquid mixture. Air ends up trapped in the meshwork of denatured proteins within the developing foam, and so the longer the mixture is beaten, the fluffier it gets. To retain the trapped air bubbles and generate peaks that stand up straight, sugar is added as a stabilizer. And eccola! Una nuvola dolce nella ciotola; a fluffy meringue is ready to bake or prepare into macarons or boccone dolce.

To create an equally amazing and delicious vegan counterpart, the egg whites would have to be substituted with an ingredient that has both water-loving and water-fearing parts. Logic may think to search for a plant-based protein alternative, but French chef Joël Roessel discovered that chickpea brine works perfectly well as a vegan egg-white substitute [1]. Coined aquafaba by Goose Wohlt (Latin for “bean water”), the leftover water from a can of chickpeas can be combined with sugar and whisked into a vegan meringue that surprisingly tastes nothing like beans. Of all the possible substitutions, why does aquafaba work in lieu of egg whites?

Photo credit: getselfsufficient/Flickr

Water leftover from cooking chickpeas, also known as aquafaba, can be used in lieu of egg whites. Photo credit: getselfsufficient/Flickr

Anne Rieder, a scientist at the Norwegian food research institute Nofima, analyzed aquafaba and revealed that the bean water contains equal amounts of proteins and carbohydrates [2]. The function of proteins in the aquafaba are similar for meringue-making; Rieber suggests that the carbohydrates may serve as an additional stabilizer by increasing the viscosity of the water portion of the foam.

To create foams like meringues, Kent Kirshenbaum, a professor at NYU, was inspired by chemistry to invent a foaming agent that is rich in saponins, currently awaiting patent approval. Saponins are a class of chemicals found in plants, including beans like chickpeas. The name derives from the soapwort plant, Saponaria, which contains the Latin root for soap, sapo; this is a fitting name, given the compound’s propensity to foam when shaken in water [3]. Like the amino acids of proteins, saponin molecules contain a hydrophobic and a hydrophilic moiety that enables them to interact with both air and water.

Whatever the reason for avoiding eggs, at least you won’t have to forfeit the heavenly delight that is a lightweight meringue cookie.

References cited

  1. Aquafaba history.” The Official Aquafaba Website.
  2. Aquafaba, what is its chemical composition?Frie kaker.
  3. Saponins.” Cornell University Department of Animal Sciences.

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung


The Science of Steamed Milk: Understanding Your Latte Art

Guest post by Christina Jayson

Photo credit: Dan Lacher (journeyscoffee/Flickr)

Photo credit: Dan Lacher (journeyscoffee/Flickr)

Watch a barista at work and you will observe the art of preparing a perfect café au lait, cappuccino, macchiato, or mocha – all of which involve different quantities of steamed milk. Behind the artistic foam hearts and milk mustaches lies a science to steamed milk.

Students of UCLA’s SPINLab (Simulated Planetary Interiors Lab) team developed an app that allows you to “calculate the power output of your steamer” and predict the “steaming time for optimal milk temperature based on amount, type and starting temperature of your milk”. Samuel May of SPINlab explains the calculations the app takes into account that allows it to predict the temperature of milk at a given time. They show that the temperature increase of milk over time is linear, allowing them to make these predictions based on a Linear Heating Model.

But what exactly happens when you steam milk? Steaming involves introducing hot water vapor (T = 250-255 °F) into cold milk (T = 40 °F) until it reaches the ideal temperature for a “perfectly steamed latte.”

While the process sounds simple enough there are a host of variables that need to be considered. Most importantly, different milks require different amounts of steaming time. As SPINLab expert, Sam warned, too high a temperature can scald the milk: scalding kills bacteria and denatures enzymes; this inactivates the enzymes and causes curdling as denatured milk proteins clump together.  Since different types of milk and dairy alternatives have different molecular compositions, this means they have different steaming temperatures. This difference all boils down to the composition of milk.

CJ_steamed milk_2

Figure 1. Milk broken down into its molecular constituents. Modified from Properties of Milk and Its Components. [3]

Milk is composed of three main components: of proteins, carbohydrates, and fat (Figure 1).

Milk is 3.3% total protein, including all nine essential amino acids; the protein content can be broken down into two main types, casein and serum. Serum, or whey proteins, contain the majority of the essential amino acids. Whey proteins can be coagulated by heat and denaturation of some of these proteins with heat; this gives cooked milk a distinct flavor. Caseins form spherical micelles that are dispersed in the water phase of milk [1]. When steaming milk, the injected air bubbles disrupt the micelles. The protein molecules then encompass the air bubbles, protecting them from bursting and leading to the formation of foam. The take away: The different protein content of different milks consequently affects each milk’s ability to maintain that frothy foam decorating your latte [2]. Whole milk results in a thicker, creamier foam and skim milk results in more foam and larger air bubbles, while almond milk is able to hold a light and long-lasting foam [2].

Table 1: Percent of protein in different types of milk and non-dairy alternative [2]

Milk % Protein
Skim milk 3.4
1% milk 3.4
2% milk 3.3
Whole milk 3.2
Soy milk 2.7
Almond milk 0.4

Lactose is the carbohydrate component of milk – a disaccharide composed of D-glucose and D-galactose. There are two forms of lactose present in an equilibrium mixture due to mutarotation, α-lactose and β-lactose. β-lactose is the more stable form, and also the sweeter form of the two [3]. When you steam milk past a temperature of 100 °C, this causes a “browning reaction,” or the Maillard reaction, in which the lactose and milk proteins – mostly caseins – react to form what is know as an Amadori product [4]. The colorless Amadori product is a molecular complex between the lysine residues of protein molecules and the lactose molecules. As the reaction continues with heating, the Amadori product can undergo dehydration and oxidation reactions, or rearrangements that lead to a loss of nutritional value and the formation of unappealing flavor compounds in milk that Sam warned could result from over-steaming.

The last main constituent of milk is the milkfat that exists as globules in the milk. Over 98% of milkfat is made up of fatty acids of different types, including saturated, monounsaturated, and polyunsaturated fatty acids. These fat molecules can also stabilize the formation of foam by surround the air and entrapping it in a bubble. While higher fat content leads to stable foam at temperatures below room temperature, milks with lower fat contents (like skim milk) are better at stabilizing foam at higher temperatures [3]. This could be due to the reduced surface tension of the fat along the air bubble surface that is a result of an increase in fat percentage. Heating up these fat molecules not only affects foam texture; when heated or steamed, the fatty acids also participate in chemical reactions, such as oxidation reactions, that can give rise to an undesirable flavor [5].

For the lactose intolerant and fans of non-dairy alternatives, you may be wondering how lactose free options such as soy or almond milk compare. Their steaming temperatures differ mildly due to their distinct properties – for example, almond milk has a lower protein content (Figure 2). According to the experience and experimentation of expert baristas, certain brands of soy or almond milk can hold a foam better than others; the science underlying this phenomenon still remains to be determined.

Table 2: Ideal steaming temperatures for milk and non-dairy alternatives [6]

Milk Soy Milk Almond Milk Coconut
150 °F 140 °F 130 °F 160 °F

The moral of the story is that each component of milk contributes to its ability to froth and foam, and steaming influences each of these components. With this knowledge, you can wisely choose your milk at Starbucks depending upon your foaming desires, or simply download Sam’s app and perfectly steam your milk at home.

References cited

  1. O’Mahony, F. Milk constituents. Rural dairy technology: Experiences in Ethiopia, Manual No.4; International Livestock Centre for Africa Dairy Technology Unit, 1988.
  2. Blais, C. The Facts About Milk Foam. Ricardo, [Online] November 2014;
  3. Chandan, R. Properties of Milk and Its Components. Dairy-Based Ingredients.; Amer Assn Of Cereal Chemists, 1997; pp 1-10.
  4. van Boekel, M.A.J.S. Effect of heating on Maillard reactions in milk. Food Chemistry. 1998, 62:4, 403-414.
  5. Walstra, P. Dairy Technology: Principles of Milk Properties and Processes; CRC Press, 2013.
  6. Dairy Alternatives – Soy, Almond, Coconut, Hazel, Cashew. Espresso Planet. [Online] April 2013;

Christina Jayson is a recent UCLA Biochemistry graduate about to embark on her Ph.D. journey at Harvard.

Apple Pie with Peanut Butter Mousse

The Science of Pie – May 19, 2013
People’s Choice Award
Elan Kramer, Caleb Turner (Team “Insert Team Name Here”)

This student duo thought outside the box with this creative apple and peanut butter pie. To create the ultimate peanut butter experience, the team experimented with the effect of egg white content on the texture and density of the peanut butter mousse.

TeamInsertTeamNameHere

photos courtesy of Patrick Tran

Egg white content affects mousse texture. (A, B) Team “Insert Team Name Here” visualized the air bubbles incorporated into peanut butter mousses prepared with different amounts of egg whites. (C) Using image processing techniques, they calculated the mean (red) and median (blue) air bubble areas as a function of egg white content. Their results show that there is indeed an optimal egg white content for creating an light, airy mousse. (D) An egg white is made up of many proteins suspended in water. Whipping incorporates air bubbles into the egg whites, causing the proteins to unfold as they are exposed to air. Denatured proteins [link to ceviche recipe] form networks at the liquid/air interfaces that stabilize air bubbles within the egg white foam.

The Recipe
Frozen apple pie with peanut butter mousse

1 large store-bought graham cracker crust

For the apple layer:
2 tbsp unsalted butter
3 firm-textured cooking apples*, peeled, cored, and sliced
¼ cup granulated sugar
1 tsp fresh lemon juice
2 tbsp powdered sugar
*Team “Insert Team Name Here” used Pink Lady and Granny Smith apples

For the peanut butter mousse:
1 cup heavy cream
8 ounces cream cheese, softened
1 cup smooth peanut butter
¾ cup granulated sugar
½ cup firmly packed light brown sugar
2 tsp pure vanilla extract
2 large egg whites

For the topping:
1 cup heavy cream
1 tbsp powdered sugar
½ cup finely chopped salted dry-roasted peanuts
2 graham crackers, crushed
1 1/2 tsp cinnamon

To prepare the apple layer, melt the butter in a large sautée pan. Stir in the apples and granulated sugar and cook over medium heat, stirring often, until tender, about 5 minutes. Stir in the lemon juice and powdered sugar and cook, stirring, for 1 minute longer. Remove from the heat and refrigerate.

To make the peanut butter cloud layer, use an electric mixer to whip the heavy cream until it holds semi-firm peaks. Cover and refrigerate.

Using the mixer, beat the cream cheese and peanut butter together until smooth. Gradually beat in the sugars, then the vanilla. The mixture will be lumpy, like cookie dough. Add the whipped cream to the peanut butter mixture, slowly blending them together with the electric mixer until smooth.

Clean and dry the beaters. Using a clean bowl, beat the egg whites until they hold stiff peaks. Fold the whites into the peanut butter mixture with a rubber spatula until evenly blended. Put mixture into the pie crust, cover loosely with aluminum foil and freeze for at least 5 hours.

When you’re ready to serve the pie, take it out of the freezer and top with the refrigerated apples. For the topping, add the powdered sugar and 1/2 teaspoon to the cream and use an immersion blender or mixer to whip. Spread over the top of the pie and sprinkle with peanuts, graham cracker crumbs, and remaining cinnamon.

Recipe adapted from Cookstr: Frozen Apple and Peanut Butter Cloud Pie