• use the Science of Foods terminology in relation to discussing foods or food products.
• use the chemistry and composition of foods to explain how it relates to the quality of a food product.
• discuss and problem-solve how processing and preparation procedures impact food quality.
• utilize value-added products to develop unique quality products.

Modified from "USDA Egg Grading Manual" 1969. Agriculture Handbook No. 75.

% Composition Whole Egg 65.5% Water 11.8% Protein 11.0% Fat 11.7% Ash

The diverse roles of egg in the recipes occur due to their particularly high water solubility, excellent foaming and emulsification capacities, heat coagulability, and high nutritive values. They contribute structure to a product that contains egg.

The quality of eggs is dependent upon the egg itself. For example, in hard cooked eggs the size of the air cell will impact whether it is oval egg or has an indentation on the end, a "less than perfect" egg for "hard boiled", deviled eggs. In custard sauces, the chalazae removal is thought, by the true chef, to improve the quality of the product. For these reasons, it is important to know the egg and factors which impact the quality of the egg and resulting products.

Below is an image of the basic egg structure. It is made up of approximately 11% shell and 89% interior. The composition of the shell is important from the viewpoint of food safety, sanitation, and esthetics. It contains calcium carbonate (94%), magnesium carbonate (1%), calcium phosphate (1%), and 4% organic matter. It is important to recognize that there has been considerable information that the hen's diet can impact the composition of the egg.

The composition of the egg yolk and white is of primary importance and the chief factor affecting the way that eggs function in a baked product.

Eggs and egg whites have been used as a clarifier. The process is as it sounds, the clearing of a liquid. Master chefs use it to clarify stock to produce clear consommes.

In the old "campfire coffee", egg white was added to coagulate around the coffee grounds and clarify it. Personally, when I have tried it, the results have left something to be desired. It is of interest that clarification is used for other items. For example, many years ago we had a relative who would give us gallons of clarified butter. This was butter that had been carefully warmed to melt the butter fat. This fat was then drawn off and the milk solids removed. The hypothesis was that it would keep "fresh" longer. Actually, theory would support this antedoctal idea. With drawing off the fat, the water and salts, syngeristic components, would no longer be available to take part in the hydrolytic rancidity reaction.

Used with permission from John Morris of the Donut Shop

Egg whites, egg yolks, whole eggs, and egg washes brushed on breads and other baked products add a rich, shiny glaze. The glaze is caused primarily by the protein and fat interaction. The simple glaze is generally made by adding a "little water" to the egg and brushing it on. In this image, John Morris is brushing an egg glaze on pigs (hot dogs) in cresants before baking.

Physicochemical Constants of Albumen and Yolk

Property/Factor	Albumen	Yolk	Reference
Bound water(%)	25	15	1
Coagulating temperature(C)	61	65	1
Density(gm/cm3)	1.035	1.035	1
Electrical conductance(mho-cm-1 x 10-3)	8.68	3.10	1
Freezing point	-0.424	-0.587	1
Heat of combustion(cal/gm	5,690	8,124	1
pH	7.6	6.0	1
Refractive Index	1.3562	1.4185	1
Solubility coefficient for CO2	0.71	1.25	1
Specific heat(cal/gmC)	0.85	0.78	1
Specific heat (cal/gmC)	0.94		2
Specific resistance (ohm-cm)	0.12	0.32	1
Surface tension (dyn/cm)	53	35	1
Vapor pressure (in % of NaCl)	0.756	0.971	1
Viscosity (poise at 0C)	25.0	200.0	1
Latent heat (But/lb)	127	81	1

1 Vadehra, D.V. and K.R. Nath. 1973. Eggs as a source of protein. CRC Critical Reviews in Food Technology 4: 193-309.

2 Cotterill, O.J. 1973. Egg Science and Technology Stadelman, W.J. and O.J. Cotterill (eds), AVI Publishing, Westport, Conn.

Quality of eggs has been defined and quantitated by the USDA. Although any egg of any quality can be laid, a high quality egg generally shows the same interior egg changes with storage as the decrease in grade reflects. These grades give an indication of the quality of eggs and, depending upon the product, may reflect the final quality of the food product for which they are used. At this time, the grade is generally assigned by a method called candling. This can be done as a automated system where light is shined through the rotating egg to reveal condition of the shell, the size of the air cell, and size, distinctness, color and mobility of the yolk. Additionally abnormalities such as blood spots, embryonic development, and spoilage are identified. The importance of these conditions in a food product depends on the specific role and function of the egg in the food product.

GRADE	DESCRIPTION
AA	Shell: clean; unbroken, practically normal Air cell: 1/8 inch or less in depth; practically regular White: clear, firm, "upright" Yolk: well centered; outline slightly defined; free from defects
A	Shell: clean; unbroken, practically normal Air cell: 2/8 inch or less in depth; practically regular White: clear, may be reasonably firm Yolk: may be fairly well centered; outline fairly well defined; practically free from defects
B	Shell: clean to slightly stained; unbroken, may be slightly abnormal Air cell: 3/8 inch or less in depth, may be free but not bubbly White: clear, may be slightly weak Yolk: may be off center, outline well defined, may be slightly enlarged and fattened, may show definite but not serious defects
C	Shell: clean to moderately stained, unbroken, may be abnormal Air cell: may be over 3/8 inch in depth, may be free or bubbly White: may be weak and watery, small blood clots or spots may be present Yolk: may be off center, enlarged and flattened, may show clearly visible germ development but no blood; may show other serious defects; outline may be plainly visible.
	Modified from Hauver, W.E. Jr. and J.A. Hamann. 1961. Egg grading manual. Agricultural Marketing Service No. 75. 52 pp., U.S. Department of Agriculture.

These differences can be seen by the images below:

Broken Out Eggs Profile of Cut USDA Grade AA, A, B, C	Hard Cooked Eggs Profile of Cut USDA Grade AA, A, B, C	Grade
		US Grade AA
		US Grade A
		US Grade B
		US Grade C

What are the grades and weight of eggs? Are they the same or different?

The weight of eggs has no relationship to grade and vice versa. The major weight classes are:

When I was growing up, in the spring we would have pullet eggs. These were eggs from hens, or pullets, that were just starting to lay. Typically, they were small and of variable size.

The grades of eggs are: AA, A, B, C. Most of the eggs on the market are AA, or A. The B and C eggs go in for pet foods and other egg products. During storage, the grade of the egg may deteriorate, although with the current knowledge of storage requirements, this is not necessarily an absolute. Actually, the major deterioration may be due to improper handling at home. It is important to know that not all eggs being laid are grade AA. Some chickens are failures and lay poor quality eggs to start with. This may be due to genetics or to the environment or feed.

The weight of the egg is important in that most recipes have been developed on the basis of a 48 gram egg. Certainly, in a fried egg, scrambled eggs or such, the size just means more. However, if one is looking at a product with a balanced formula, such as cream puffs, muffins, an angel food cake, the difference between a small egg versus a jumbo in the final product could be dynamic. As far as selection of grade, as with weight, in some products it makes a difference. In others there is none. Assuming a safe egg, it makes no difference whether an AA or a B is used in a scrambled egg. However, if being used in a sponge or angelfood cake one would have a different yield and foam stability with the two grades. Certainly, with a fried egg, sunny side up, the egg would be more attractive if a AA or A egg was used.

The coagulation of eggs is critical to many food products. Coagulation is simply the solidifying of the egg by the application of heat. In many instances, the egg in a formula will serve to glue the product together. For example, it is sometimes added to meat loaf or on the surface of okra, in both instances serving as a glue. Certainly, the coagulation of the white and yolk permits the "structure" of the product for deviled eggs. A large portion of the discussion of stirred and baked custard hinges on egg coagulation. It is of interest in the many products to know the coagulation mechanism of the yolk and the white.

Following are the general temperatures at which various egg parts and egg products will coagulate:

Generally, whole egg begins to become opaque at around 60C and increases in viscosity to 72C. At 75C it is a soft curd and increases in firmness up to 87C. Certainly, heat is the critical factor in bringing about the denaturation of the egg protein and forming structure. However, heat has many other causative factors. It should be remembered that heating the egg product itself, if (liquid or dried form) has been done during the pasteurization of eggs. This heat will decrease the functional properties of these eggs.

Again, one needs to be reminded that the rate of heating, the added ingredients, the concentration of the egg and other subtle factors will impact the range of temperature and the optimum endpoint. The work on model systems of eggs by Pawayal et al. [1946] essentially appears to indicate that there is a relationship between time and rate of heating. The faster the mixture heats the lower the point of increased viscosity.

Practically speaking, what are the implications of the differing coagulation points of the various egg parts?

When most consumers talk about egg products they likely are thinking about the whole shell eggs and the many different foods. Neff [Neff, J. 1998. Foods of Tomorrow. The Great Egg Breakthrough. Food Processing 59(1): 25.] indicates that in 1997 there were 6.443 million dozen eggs in the shell and 1.621 million dozen breaker eggs consumed. The per capita egg consumption was 171.5 shell eggs and 66.5 breaker eggs. However, there are other egg products used by the consumer, foodservice industry, and value-added portion of the food industry. Most consumers are well aware of the market for egg substitutes and egg replacers.

Although one should review egg selling sites to get the latest on available products, some of the different egg products are as follows:

Dried Eggs: (blends of whole egg and/or yolk with sugar or corn syrup) added, flake albumen, free-flowing whole egg or yolk solids, instant egg white solids, spray-dried egg white solids, stabilized whole egg yolk solids (glucose free), whole egg or yolk solids

Frozen Eggs: egg white, egg yolks, salted whole egg, salted yolks, sugared yolks, whole eggs, whole eggs with com syrup, whole eggs with added yolk (fortified), whole eggs with yolks and corn syrup, yolk and white blends w/wo sweeteners or salts

Refrigerated Liquid Egg Products: egg whites, egg yolks and various mixtures of these.

Specialty Products come in a wide variety of forms. Some of my favorites are the precooked egg yolks/whites and cooked egg white with a center tube of cooked yolk. There are boiled eggs available for purchase by institutions. One can order the "real egg" in about any form desired.

There are many products that serve as egg substitutes or replacers. Eggs have also been used as substitutes for other ingredients. Neff reported the work of Dan Neumeister in developing a heat-denatured egg yolk to substitute for potassium bromate to improve the texture and outward appearance of bread.

What is the effect of the egg product in a custard? Funk et al. 1969 has plotted the heat penetration of custards as essentially rise steadily to 74C and than slowing down in rate until approximately 82C and rising again to above 87C. They observed that the type of egg processing [foam-spray, frozen, freeze, spray-dried] did make a slight difference in the heating rate. Workers have hypothesized that the actual coagulation occurs as a two step process. The first step is the actual denaturation of the protein and the second step is the protein-protein interaction and the formation of a gel or increased viscosity. Interesting, Lowe [1942] observed that forewarming of the milk may decrease curdling and shortening cooking time. However, it is important to remember that 0.75% of the milk protein is heat coagulable.

Which of the following are egg custards?

Custards may be altered by manipulation or ingredient variation. Because egg is the primary structural ingredient of a custard, some differences are seen when fresh, frozen, old, dried or egg substitutes are used. The egg source, for example duck or turkey, also influences custard quality. Milk, although not as structurally important as egg, contributes to the viscosity or gel strength of the finished product. Calcium ions present in the milk are needed in the formation of a thicker custard, as custards made with water will not gel or thicken. Differences in processing will also influence the custard quality. Nonhomogenized milk produces a baked custard with a thinner crust, more delicate browning and better sheen than those custards made with homogenized milk. For example, stirred custard usually is considered to have "more body". Sugar is also important to the viscosity and gel strength of custards. Sugar tends to increase the denaturation temperature of the egg proteins resulting in a less stiff product. Salt and flavoring have no appreciable affect on custard quality other than for taste.

The proportion of ingredients is important to custard quality. The concentration of egg protein is proportional to the viscosity or gel strength of the custard. With increasing concentration, a custard sauce becomes more viscous and the gel strength of a baked custard firmer. Also, with increased egg protein, the product becomes more sensitive to end point temperature. End point temperature is the point at which optimum denaturation has occurred without curdling or syneresis. Milk serves to dilute the egg protein so less viscosity and gel strength are observed with increasing proportions of milk. Because sugar increases the denaturation temperature of egg proteins, increased sugar concentrations results in softer custards. At a 30% sucrose concentration, a custard will not gel at all.

Producing a good quality custard depends on a number of factors. In addition to the proportion and ingredient variation, temperature and rate of cooking are important. A custard heated slowly begins to thicken at a lower temperature, thickens gradually over a wider temperature range and reaches doneness at a lower temperature. On the other hand, a custard heated rapidly must be heated to a higher temperature before thickening begins and overcooking, resulting in curd formation or porosity, occurs easily. Syneresis or weeping results as the curds separate from the serum. Slow cooking can be achieved by placing the baked custard mixture in a waterbath in the oven or by using a double boiler with a stirred custard. Endpoint is indicated when the stirred custard "coats the spoon", or when a knife inserted into the baked custard "comes out clean".

Which of the following custards was cooked the longest? Which of the following custards could represent the custard having the greatest amount of sugar? Which of the following custard could likely represent the custard having egg white substituted for the whole egg?

When one turns to a recipe or formula and it lists eggs as an ingredient, it is usually understood to be whole chicken eggs. The egg itself and the method of processing of the food product it is in will make a difference in the reaction of cooking. The effect of ingredients in products will make a difference. Certainly it will vary depending upon the product and the function of the egg. Following are some affects.

	Milk's contribution in egg products such as custards is underestimated. As early as 1942, Carr and Trout reported research that indicated the cooking time for custards made with homogenized milk took 15 to 20 minutes longer than custards made with nonhomogenized milk. Heat penetration was slower. Additionally, viscosity and gel strength was greater with homogenized milk. However, this webber has observed that milk's effect on egg gelation is not well documented. Milk contains electrolytes which will enhance viscosity and gel strength.
	Sugar will inhibit and delay denaturation of the egg proteins, depending upon the product. In a custard, it delays coagulation so that equivalent thickening (from the standard) will occur only at a higher temperature, if at all. In the production of foams, it has been shown that adding sugar will delay the formation of an egg white foam. However, once a foam is formed, it is more stable.
	A variety of factors may influence the pH of eggs. Shimada and Matsushita (1980) observed that pH and protein concentration affected coagulation of egg albumin. The net charge of egg albumin increased up to pH 8, plateauing up to pH 11 at which time no coagulation occurred. The charge would increase as concentration increased. This is due to the change of the proteins themselves. Certainly if one adds acid to a egg containing product it will coagulate faster. This effect is often utilized. For example, angelfood cake foam has lemon juice or cream of tartar added as a stabilizer.
	The amount, how it is processed and type of eggs makes a difference. The part of the egg will impact the functional properties within an egg product. Researchers have determined that egg yolk will also coagulate, beginning at ~65C, losing fluidity at 70C and coagulating at 85C. Woodward and Cotterill (1987) felt that the major denaturation occurred in egg yolk at 68C to 70C. Egg white will coagulate approximately 5C higher. As with egg white, there was significant pH-temperature interdependence. Other workers [Shimada and Matsushita, 1980] have observed that coagulation increased with increased protein level and concentration. This is of particular importance when using selected fluid or dried egg products. The method of processing the egg makes a difference. Research done by Funk et al. in1969 plotted the heat penetration of custards, rising steadily to 74C and then slowing down in rate until approximately 82C and rising again to about 87C. They observed that the type of egg [foam-spray, frozen, freeze, spray-dried] did make a slight difference in the heating rate. Another study conducted by Downs et al [1970] observed that spray-dried eggs tended to coagulate faster than frozen, freeze-dried and foam-spray-dried eggs.

Powrie, W.D., H. Little, and A. Lopez. 196 . Gelation of egg yolk. Journal Food Science :38.

Egg safety is critical to minimize the problems of food infection and poisoning. There are a number of truisms necessary:

albumen: Variant spelling of albumin, used generally to mean white of egg.
albumin: A group of simple proteins composed of nitrogen, carbon, hydrogen, oxygen, and sulfur that are soluble in water. Albumin is usually derived from egg white and employed as an emulsifier in foods and cosmetics. May cause a reaction to those allergic to eggs, and in large quantities can produce symptoms of lack of biotin, a growth factor in the lining of the cells. Often used as a non-specific term for protein (e.g. albuminuria means protein present in urine), but strictly refers to simple proteins soluble in water and coagulated by heat, such as ovalbumin in egg, serum albumin in blood, lactalbumin in milk.
beading: the appearance of tiny droplets of syrup on the surface of a baked meringue as it stands
chalazae: is the thick "cord" that anchors the yolk to the egg shell.
clarify : to make clear a cloudy liquid such as heated soup stock by adding raw egg white and/or egg shell; as the proteins coagulate, they trap tiny particles from the liquid that can then be strained out. Is, broadly speaking, a process by which some harmless matter is added to, or some harmless process acts upon, a liquid body in such a manner that a fine insoluble network is formed throughout, which either settles down or rises as scum, entangling the opaque particles, however minute, that are floating about and constituting the cloudiness; these the network bears with it in its upward or downward progress. The process of clarifying is therefore purely mechanical.
coagulate: to form a clot, a semisolid mass, or a gel, after initial denaturation of a protein; to produce a firm mass or gel by denaturation of protein molecules followed by formation of new crosslinks
cream of tartar: is a white, crystalline, acidic compound obtained as a by-product of wine fermentation and used chiefly in baking powder. is the acid salt of tartaric acid which occurs as crystals or powder. It has a solubility of one gram in 165 mL of water at 25C and one gram in 16 mL of boiling water. The acidulant is used in chemical leavening to release carbon dioxide which produces the loaf volume. It has limited reactivity in the cold so when used in reduced temperature, batters has little gas evolution during the initial mixing. At room temperatures, it has a relatively fast reaction rate. It is used in baked goods, crackers, and candy. The chemical name is potassium acid tartrate, potassium bitartrate. potassium acid tartrate, the partial salt of tartaric acid, an organic acid; the acid salt of tartaric acid; a weak acid substance commonly added to fondant to produce variable amounts of invert sugar from the hydrolysis of sucrose.
custard: May refer to custard powder, or to egg custard. Egg custard is composed of milk and egg cooked together. Is a cooked or baked mixture consisting mainly of eggs, milk, and sugar. A custard is made of egg, milk, sugar and usually salt and flavoring. Through application of heat and manipulation, custards can become a viscous sauce or a semi-rigid gel. In each case denaturation of the egg protein, ovalbumin, conalbumin and ovoglobulin, is primarily responsible for the thickening of the custard. Stirred custards are cooked on top of the range while gel type custards are usually baked. Custards may be altered by manipulation or ingredient variation. Because egg is the primary structural ingredient of a custard, some differences are seen when fresh, frozen, old, dried or egg substitutes are used. Eggs other than form a chicken, for Example duck or turkey, also influence custard quality. Milk, although not as structurally important as egg, does contribute to the viscosity or gel strength of the finished product. Calcium ions present in the milk are needed in the formation of a thicker custard, as custards made with water will not gel or thicken. Different processed milks will also influence the custard quality. Nonhomogenized milk produces a baked custard with a thinner crust, more delicate browning and better sheen than those custards made with homogenized milk. The stirred custard usually is considered to have "more body". Sugar is also important to the viscosity and gel strength of custards in that sugar tends to increase the denaturation temperature of the egg proteins resulting in a less stiff product. Salt and flavoring have no appreciable affect on custard quality other than for taste.
denaturation: a change in the molecular structure from the native structure of a protein. Is a change in a protein molecule, usually by unfolding of the amino acid chains, with a decrease in solubility.
disulfide linkages: bonding through two sulfur atoms (-s-s-)
eggs: generally from fowl. egg grades: For chickens, AA, A, B, C. egg wash: egg yolk and/or white mixed with a small amount of water or milk and brushed over a bread product prior to baking. An egg wash gives color and gloss to the product.
egg white: 87.8% water, 10.8% protein, 0.6% ash. Composed of outer layer of thin white, layer of thick white, richer in ovomucin, and inner layer of thin white surrounding the yolk. Eggs vary in ratio of thick to thin white, depending on the individual hen. Higher percentage of thick white desirable for frying and poaching (helps the egg to coagulate into small firm mass instead of spreading); thin white produces larger volume of froth when beaten than does thick. Proteins are ovomucin, ovalbumin, ovomucoid, ovoglobulin and conalbumin.
egg yolk: is a yellow portion of the egg, representing approximately 35% of the edible egg. It is composed of approximately 49% water, 16% protein, 32% fat and trace carbohydrate. It is used as an emulsifier in mayonnaise, salad dressing, and cream puffs. It is also used as a source of color.
emulsion: the dispersion of one liquid in another with which it is usually immiscible, for example, oil in water. An emulsion is a mixture of two or more normally nonmixable liquids shaken so thoroughly together as to appear homogenized, for example, as is done with salad dressing. Most oils form emulsions with water.
flocculated: is separated into small woolly or fluffy masses.
foam: is the dispersion of a gas in a liquid such as a beaten egg-white mixture.
gel: A sol or colloidal suspension that has set to a jelly. Acolloidal dispersion that shows some rigidity and will, when unmolded, keep the shape of the container in which it had been placed; a semi-rigid structure at room temperature. This dispersion does show some rigidity or moldability.
lipoproteins: are proteins combined with lipid or fatty material such as phospholipids.
protein efficiency ratio: A measure of the nutritive value of proteins carried out on young growing animals. Is defined as the gain in weight per gram of protein eaten. The maximum values, e.g. egg protein, are about 4.4. Zero values are obtained for those proteins which, when fed alone, do not permit growth, but may still have some limited value.
sol: A colloidal solution, i.e. a suspension of particles intermediate in size between ordinary molecules (as in a solution) and coarse particles (as in a suspension). A jelly-like sol is a gel.
souffle: is a cooked heated egg foam with whitesauce as a stabilizing. Generally has meat, cheese, or some other flavoring as well.
surface activity: is the lowering of the surface tension of a liquid because of agents that tend to concentrate at the surface.
surface tension: is the tension or force at the surface of a liquid that produces a resistance to spreading or dispersing; due to the attraction of the liquid molecules for each other.
syneresis: is when two or more factors act co-operatively, so that their combined effects when acting toghether exceed the sum of their effects when each acts alone.
viscosity: Term used of liquids to define their resistance to flow (i.e. the internal friction). Viscosity is a critical factor in use of vegetable gums. The readings below only reflect the actually viscosity indicated by the ability of stress and strain from an instrument. Hydrocolloids may contribute a sliminess to a product which changes their viscosity. For example, carboxy methyl celluose, locust bean gum, methyl cellulose, pectin, and sodium alginate are considered to be slimy hydrocolloids. Carrageenan, guar, karaya, and tragacanth are less slim and starch is nonslimy.
vitelline: generally refers to the membrane or proteins of concern to the yolk.