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| Terminology
Beverages Bread Carbohydrates Cereals Creampuffs Crystallization Egg Energy Fats & Oils Flour Mixtures Food Systems Fruits & Vegetables Leavening Meat, Fish, Poultry Milk Muffins Pastry pH Popover Protein Quickbreads Safety Sensory Shortened Cake Sponge Cakes Starchs Sugars Vegetable Gums Water |
Custards Safety Souffles Sponge Cakes
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.
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.
Certainly the grade of the egg impacts its "quality"; however, there are
many other conditions. Eggs are graded as a freshly laid egg. This freshly
laid egg may be a AA or even a C graded egg to start with. However, all
eggs will begin to deteriorate upon storage. The question and problem is
to minimize storage losses. Storage in a room where temperature is maintained
slightly above the freezing point [-2C; 28F) of eggs and humidity of 90%
will maintain quality of eggs for several weeks. As temperature and/or humidity
increases, the storage time will decrease. The following table indicates
changes with storage and possible reasons for the change.
Images Showing Egg Quality
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.
These differences can be seen by the images below:
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:
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".
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.
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
Are brown eggs better than white eggs from a food quality viewpoint? From a nutritional viewpoint? What are the grades and weight of eggs? Are they the same or different? Why should the food preparer care? What is the structure of a typical eggs? Of what importance is this? Why does a egg float? What are the changes which occur in an egg during storage? As eggs age they lose carbon dioxide and become more alkaline in pH. Several visual changes accompany this. Describe four of the visual changes that indicate a lower quality egg. What is the significance of a thin runny versus a thick viscous egg white? What is the difference between egg albumen and egg albumin? What are the temperatures at which the different components of eggs coagulate?
How does the following affect the coagulation temperatures of egg:
Describe the differences and/or similarities between the following
terms: What is the most striking difference between a poached fresh egg and a poached deteriorated egg? What would be the ideal conditions for storing eggs in the home and why? Which component of the egg coagulates at the lowest temperature? What is the effect of combining the egg yolk and egg white? Why? If you have made baked eggs and found them to be tough and undesirable, what you do differently next time? Why does a hard cooked egg have a undesirable green film on the yolk? How would one avoid a dark ring around the yolk of a hard-cooked egg? Why do dried egg whites turn brown? How do they prevent it? Does the egg substitute make a suitable replacement for fresh eggs? Why or why not? What are egg replacers? What are the top grades of eggs?
What are the weight classes of eggs?
Why do we care what type of egg (from what species) one has?
Are eggs with blood spots safe to eat?
What is the likely reason for the thinning of egg white- indicate
major protein involved and indicate possible mechanisms?
Why do we care what the physicochemical properties of eggs are?
What is the advantage of knowing them?
Complete the following
chart and indicate the nutritional and medicinal protein sources
and their effect or advantage for those that eat cooked and/or raw eggs.
Explain the possible effect of removing ovalbumin and replacing
it with ovomucoid in an angel food cake.
Which component of the egg coagulates at the lowest temperature?
What is the effect of combining the egg yolk and egg white? Why?
Which component of the egg coagulates at the lowest temperature?
What is the effect of combining the egg yolk and egg white? Why?
Why do scrambled eggs stick to the bottom of the pan particularly?
An egg in the shell which has been simmered in water for 20 to 25
minutes rather than boiled would likely have what quality characteristics?
Can one decrease the cholesterol content of eggs?
Why and/or how do egg substitutes and/or replacements differ from
whole eggs? What is the affect of such replacement?
A recipe I have calls for 10 eggs. I don't want any left over as
I am leaving on vacation. What size should I get?
Practically speaking, what are the implications of the differing
coagulation points of the various egg parts?
Updated: Wednesday, October 24, 2007. |
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