A note on cold mousses

An egg foam can also be used as scaffolding for cold mousses and cold soufflés. The foam is stabilized when cold congeals fats and gelatin protein. Chocolate mousse is a prime example. Egg yolks are combined with melted chocolate and finely ground sugar and heated to around 100 degrees F/38 degrees C. The mixture is then combined with 3 or 4 times its volume in stiffly beaten egg whites. The cocoa solids and sugar absorbs much of the moisture from the egg whites and the bubble walls are reinforced. The mousse is spooned into dishes and refrigerated for several hours. As the mousse cools down, the cocoa butter congeals into a rigid solid.

Meringues

A meringue is a sweetened egg foam that generally stands on its own. Meringues obtain their stiffness and stability from sugar and heat. They are often baked slowly at low oven temperatures of 200 degrees F/93 degrees C. When browned in a hot oven or under a broiler, the surface gets crisp while the interior remains moist.

Meringues have a lot of sugar. The proportion of sugar to egg white ranges from 1:1 to 2:1. The higher, a 67% sugar content, is typical of jams. At this concentration, sugar reaches its water solubility at room temperature. Granulated sugar does not dissolve completely in a hard meringue. It leaves a gritty texture and weeping syrup drops. Confectioner's sugar or premade syrup are better suited for meringue use.

There are two main categories of meringues: uncooked and cooked.

Uncooked meringues are the simplest and most common. They vary in purpose and firmness based on the timing of the cook's addition of sugar. The lightest meringues are obtained by folding in the sugar only after the foam is formed. The sugar dissolves into the bubble walls and adds bulk and cohesiveness. These meringues are suitable for a spread pie topping or folding into a mousse or chiffon mix. If the sugar is beaten into the foam as it forms, it noticeably tightens the foam texture. These meringues get stiffer and can be shaped. Some cooks reverse the technique by beating the eggs gradually into the sugar. This process takes longer but a cook can form a foam in autopilot as it demans little attention. The resulting meringues are denser and less brittle. Therefore, the earlier the sugar is added, the firmer and finer the meringue.

Cooked meringues are more complex and are generally more dense. Heat incorporates the sugar better in the meringue and stabilizes the protein network into a solid structure. There are two basic cooked meringues:

• The Italian meringue is a syrup-cooked meringue. Sugar is made into a syrup first by heating sugar and water to 240 degrees F/115 degrees C. The whites are whipped to stiff peaks and then the syrup is streamed into the foam and beaten. The result is a fluffy, fine-textured, stiff foam. It can be used to decorate pastries or blend into batters and creams. Note: The heat from the hot syrup is not enough to kill salmonella as much of its heat gets lost to the bowl, whisk, and air.
• The Swiss meringue (similar to the French meringue cuite) is prepared by heating eggs, acid, and sugar in a hot bath and then beaten into a stiff foam. This preparation pausterizes the egg whites before forming the foam. This meringue can be refrigerated for several days and is usually pipped into decorative shapes.

Egg, bowl, and whisk

Just about any egg, bowl, and whisk can provide a good foam. Here are some tips to consider:

• Older eggs at room temperature have thinner whites and foam more quickly, but by the same token a thin egg white is more likely to drain and older yolks rupture more quickly, often leaving traces of yolk in the white.
• Fresh eggs take longer to beat but make a more stable foam.
• Cold yolks are easier to separate from whites. The whipping process warms the whites anyway.
• Egg foams can also be whipped from dried egg whites.
• Use a bowl large enough to accomodate an eightfold expansion of volume.
• If beating by hand, a large "balloon whisk" aerates a greater volume of whites at a time.
• When using a mixer, choose a beater that both spins and traces a curlicue path for a more even foam. Other mixers and beaters work, but less efficient beaters produce a denser texture.

Effects of other ingredients

• Salt weakens structure as its ions Na+ Cl- compete for bonding sites on the unfolded proteins. It's best to add salt to the other components of a dish rather than the foam itself.
• Sugar both hinders and helps foam making. When added early, it delays foaming and reduces the ultimate volume and lightness. At this point, the sugar interferes with the unfolding and bonding of the proteins. The syrup-egg mixture is also heavier and harder to spread into bubbles. It takes twice as long to foam. However, sugar improves foam stability by slowing down drainage from bubble walls. In the oven, dissolved sugar delays moisture loss until after ovalbumin has had time to coagulate and reinforce the foam. Sugar also adds its own reinforcement to the structure in the form of cotton-candy-like strands of dry sugar. Most times, sugar is added to the egg whites after the foam has already begun to form, though sometimes its added at the beginning for a more firm, dense foam.
• Water in small amounts can increase the volume and lightness of foam, but since it thins whites, it is more likely that some liquid drains from the foam.

Protecting the foam

Though proteins are responsible for giving foams structure, they can also destabilize them. If whipped too long, the proteins form tight bonds that squeeze out the water. This causes the foam to lose volume, become grainy, and separate into a dry froth and runny liquid. There are simple ways to prevent this catastrophic collapse:

The presence of copper or silver in foaming egg whites binds to reactive sulfur groups. This renders the proteins unable to form other strong bonds, which prevents proteins from getting too close to each other and collapsing the foam. For this reason, the use of a copper bowl for whipping egg whites has long been recommended. If a copper or silver plated bowl is not available, the cook may add a pinch of powdered copper supplement to obtain the same result.

Bonds with sulfur groups can also be prevented by adding an acid such as 1/8 tsp cream of tartar or 1/2 tsp of lemon juice. The acid boosts the number of available hydrogen (H) ions in the mix, making it harder for the S-H groups to shed their hydrogen and form strong sulfur bonds with anything else.

Other things to keep in check include egg yolks, fats/oils, and detergent. Traces of these three things interfere with protein bonding. Their presence does not prevent a foam from forming, but it takes longer and the quality suffers. Fats and yolks can be added once the foam is formed.

Tips on egg handling and storage

• Egg grades are classified by the USDA as an approximation of quality at the time the egg was laid. Only the top two grades, AA and A are seen in stores.
• Eggs have the ability to remain edible for weeks as long as they are kept intact and cool. Egg deterioration begins as soon as the egg is laid. The egg suffers changes in pH from acidic to alkaline. At more alkaline pH, the egg whites clear as proteins repel each other instead of forming light-blocking complexes. The whites become more runny. The yolk becomes weaker due to an influx of water that increases its volume and stretches its membranes.
• One can test egg freshness by placing eggs in a container filled with water. Fresh eggs sink rapidly to the bottom. Older eggs stay afloat longer.
• An egg deteriorates as much in a day at room temperature as in four days under refrigeration.
• It's best to buy eggs out of a cooler, not from an open shelf. Keep cold.
• An airtight container slows moisture loss and absorbion of odors.
• To freeze eggs, remove them from the shell. Freeze whites separate from yolks. It's best to mix yolks with a 1 tsp salt, 1 tbsp of sugar, or 4 tbsp lemon juice per pint to prevent proteins from aggregating and obtaining a pasty consistency once thawed. To freeze whole eggs, half the treatment for yolks.
• Salmonella infection of eggs is low, but still a problem. Salmonella is killed if eggs are cooked at 140 degrees F/60 degrees C for 5 minutes, or at 160 degrees F/70 degrees C for 1 min.
• If eggs are to be consumed or used raw, try pasteurized eggs or freeze dried eggs.
• One can tell the difference between a cooked egg vs a raw egg by giving it a spin on its side. If its smooth, then it's cooked. If it is wobbly, it is raw.

The white

The white accounts for two thirds of the shelled egg's weight. It is made of 90% water. The rest is made up of proteins, minerals, fatty materials, vitamins, and glucose.

The proteins in the whites play important roles in protecting the embryo. Some proteins block the action of digestive enzymes. Others bind tightly to vitamins and/or iron. One protein inhibits the reproduction of viruses, and another digests the cell walls of bacteria. The egg white is a chemical shielf against infection and predation.

The following proteins are important for the cook:

• Ovomucin accounts for <2% of albumen but has the most influence on the eggs culinary value. Ovomucin pulls together the proteins into an organized structure. It is what makes the thick egg white thick. It gradually desintegrates, so older eggs have a more runny texture.
• Ovalbumin is the most dominant egg protein. Its role is not entirely understood but it is thought to help inhibit protein-digestive enzymes. It is the only egg protein to have reactive sulfur groups, which strongly contributes to the flavor, texture, and color of cooked eggs. Ovalbumin becomes more heat resistant as the egg ages, so fresher eggs need less cooking than older eggs.
• Ovotransferrin holds tightly to iron. It is the first protein to coagulate when an egg is heated, thus it determines the setting temperature. Whole eggs set at higher temperature than egg whites because ovotransferrin binds to the iron in the yolk and becomes more resistant to coagulation. Ovotransferrin changes color when bound to metals, which is why whites whipped in a copper bowl turn golden and whites supplemented with ground-iron turn pink.

Egg whites are highly immunogenic. Portions of ovalbumin tend to be responsible. Sensitivity to egg whites develops early in life. Pediatricians recommend that infants and children under 1 do not consume egg whites.

The yolk

The yolk accounts for over a third of the eggs weight and its purpose is almost exclusively nutritive. It carries three-quarters of the calories of the egg and most of the iron, thiamin, and vitamin A. It obtains its color from the plant pigments xanthophylls found in the hen's feed. The yolk also contains amylase, a starch-digesting enzyme.

The yolk consists of spherical compartments and tightly packed. These chambers are filled with water that suspend tiny subspheres that contain water and phosphorus-rich proteins where the iron in an egg is bound. Suspended in the water inside these subspheres are low density lipoproteins that contain aggregates of fat, protein, cholesterol and phospholipids, mainly lecithin.

Cholesterol is an essential component of animal cell membranes, therefore, it is a substantial component in the egg. One large egg contains around 215 mg of cholesterol, while an equivalent portion of meat has about 50 mg. With that said, concerns of high blood cholesterol and increased risk of heart disease have placed dietary restrictions on yolk consumption. However, recent studies suggest that egg consumption has little effect on blood cholesterol which is more susceptible to saturated fats than cholesterol itself. Most of the fat in egg yolks is unsaturated.

Egg yolks are far less allergenic than whites and can be safely consumed by infants.

Egg shape

The following picture details the inner structure of a chicken egg:

 

taken from: http://food.oregonstate.edu/learn/egg.html

Keeping in mind the picture above, let's explore the structure of the egg.

The egg begins with the germ cell atop the yolk. The germ cell contains the hen's chromosomes. Over time, the germ cell accumulates a white, primordial form of yolk, the white yolk. Close to the time when the hen is preparing to lay the egg, the germ cell accumulates yellow yolk, which is mostly composed of fats and proteins. The color of the yolk reflects the pigments in the hen's diet. The yolk becomes large enough to potentially feed a developing chick for 21 days.

The yolk is released from the hen's ovary into the oviduct, where the germ cell can be fertilized if the hen mates. Most eggs are not fertilized. The egg white forms from proteins secreted here, mainly albumen (albumin proteins particular to eggs). Four alternating thick and thin layers of protein form the egg whites that surround the yolk. The chalazae is a twisted albumen anchor that connects the yolk to the shell. It allows the yolk to rotate while suspended in the middle of the egg.

On the outer side of the white, lies an antimicrobial protein membrane that connects everywhere except for the air pocket that is available for the hatching chick to breathe. The shell consists of calcium carbonate and proteins. Finally, a thin proteinaceous cuticle covers the shell which initially plugs the pores in the shell. The cuticle prevents water loss and blocks bacteria from entering the egg. Gradually, the cuticle fractures for the purpose of allowing oxygen in for the developing chick.

The color of the egg comes along with the cuticle. Egg color is determined by the genetic make up of the hen. If the hen has white plumage, the egg is white. If the hen is pigmented, such as the Rhode Island Reds, the eggs are brown. There is neither a nutritional nor a taste difference between brown eggs and white eggs.

Note: This post reminded me of one of my favorite essays by E.B. White, Riposte, where he discusses the preferences of the brown egg versus the white egg. I highly recommend it for an entertaining, and logical view of color.

Evolution and history of eggs

The egg is one of two reproductive cells (the other being the sperm cell), which when fertilized accomodates two gene sets, divides, and differentiates into the embryonic organism. It provides food for the inital stages of growth. Eggs are nutritious because they are designed to be food; they are designed to support new creatures until they are able to fend for themselves.

History dates back to the development of sexual reproduction in multiple-cell organisms. Around 300 million years ago, land dwelling reptiles developed self-contained eggs with shells that prevented fatal moisture loss and provided enough nutrients to support embryonic development into a fully formed animal. About 100 million years later, birds came along. Bird eggs developed a mineralized shell and antimicrobial defenses. These refinements made bird eggs a perfect human food. The egg contains a sizeable and balanced portion of animal nutrients, it is pre-packaged, and it stores well with little or no effort.

The genus Gallus, to which the chicken belongs, came along around 8 million years ago; but the chicken did not become domesticated until around 7500 BCE. From then, the eggs of different fowl made their way through many cultures and peoples. Chickens became prized because of their egg-laying behavior. Some fowl will only lay a certain number of eggs at a time, no matter what happens to the eggs. Others, including chickens, will lay eggs until they accumulate a certain number in their nest. If one of the eggs is taken away, the chicken will lay another to replace it and may do so indefinitely. Humans became the unrelenting predator who bound chickens to lay eggs day after day.

Bird eggs have been cooked probably since the discovery of fire. Salting and pickling eggs were performed by the Ancient. By the time of the Romans, many different recipes and uses were found for eggs. By medieval times, the French had mastered omelets. Yolk-based sauces and egg-white foams developed after the Renaissance.

Between 1850 and 1900, the chicken underwent an evolutionary change. The West was introduced to the Cochin, a Chinese breed of chicken, and a "hen fever" exploded. Hundreds of new breeds were developed. Breeds became prized for their meat or their egg-laying abilities. Today, most of the genetic diversity generated has disappeared. In the US, most chickens today are the product of four purebred grandparents.

The 20th century brought changes in industrialization and mass production. Today, most of the eggs come from egg factories, some of which house up to 1 million egg-laying hens. Most hens live in a cage-system which standarizes diet and social development; and streamlines egg collection, washing, and packaging. Hens in the US lay an average of 250 eggs a year, and suffer less than 5% mortality rate as opposed to free-range hens in the previous century, which laid around 100 eggs a year and suffered 40% mortality rate. The differences are attributed to improved housing (less exposure to the elements, disease, pecking orders, and predators), and more equitatable feeding. Furthermore, mass production exploded as refrigeration made fresh eggs readily and cheaply available. In many areas, eggs are available to the consumer within a day of it being laid by the hen.

Concerns have been raised about making chickens into biological machines. "Free-range," "organically-fed," and other specialty eggs have become available. While there is a benefit to their availability, people pay a hefty price for their concern, as much as 3x more. Even so, there are no clear guidelines as to what those labels mean. "Free range" in some cases only means a larger cage. Switzerland is the only country that requires that all hens have free access to the outdoors.

Lesson 6: Meringues

This week discussion revolves around the wonderful egg, with an emphasis on the whipping quality of egg whites. Topics include:

An introduction to eggs
Egg foams
Beating techniques

The culminating recipe is a lemon meringue tart. Hope you join me!