Lesson 19 :Eggs - Processing, Preparation and Preservation
Stability of the foam
Stability is measured by finding how much liquid drains from it on standing. This is usually done by transferring the foam to a funnel and measuring or weighing the liquid that drains from it. More the water drains means the foam is less stable.
Factors affecting egg white foams
Effect of beating time: As the time of beating egg white is increased their volume and stability increase at first and then decrease. The actual time required depends on the type and speed of the beater. Higher the speed, shorter the period of beating required. Maximum stability is reached before maximum volume.
Type of beater used: If the beater has thick blades or wires, they do not divide egg whites as easily as fine wires and resulting air cells are therefore larger. Egg whisks sometimes give a larger volume of beaten egg mass than do rotatory types of beaters but the cells are larger.
Type of container in which eggs are beaten: Bowls with small rounded bottoms and sloping are preferable to bowls with large flat bottoms because, in the former, the beater can pick up the egg mass more easily. The size of the bowl must obviously be adapted to the amount of egg to be beaten. If whisks are used for beating egg whites, a large plate is preferable to a bowl for holding the whites because of the over-and-over strokes that are used.
Temperature:egg white can be beaten more readily at room temperature than at refrigerated temperature possibly because of lowered surface tension at higher temperature.
Thick and thin whites : Thin whites can be beaten more readily and produce greater volume than thick white. Stored eggs may beat more quickly than those fresh eggs as in stored eggs the white is thin. Thick whites seem to produce more stable foam even though thin whites may initially beat to a larger volume. The volume of cooked products such as cakes and meringues is greater when thick whites are used rather than thin whites.
Addition of acid: Addition of acid to egg white makes the foam more stable but increases the time necessary for beating. Cream of tartar is more effective in increasing the stability than acetic or citric acid. Acid is best added during the first portion of beating period. The addition of acid to egg white also makes the foam more stable to heat. e.g., meringue.
Addition of fat: The presence of fat interferes with foam formation and decreases the foam. Similar effect is observed when yolk is added to white. This effect is the result of the fat probably the lipoproteins, in the egg yolk which may form a complex with proteins in the white.
Addition of salt: Addition of salt to egg white (1g to 40g egg white) or whole egg lowers the quality (volume and stability) of the foam as it becomes less elastic. The addition of salt to fresh egg white decreases the stability of foam unless the beating time is increased from 6-9 minutes. The addition of salt to whole eggs before beating results in a foam of small volume that would not form peaks. Sponge cakes made from such a foam has smaller volume and less tender when salt is added to the egg rather than adding salt to the flour.
Addition of water: Dilution of egg white with water upto 40 percent of the volume of egg increases the volume of foam but decreases the stability.
Addition of sugar: If sugar is added before beating is started, extensive beating is needed to produce a foam. Once formed the foam is stable and very fine although the volume may be less. The shine of egg white foam with added sugar is in part to the prevention of coagulation of proteins with accompanying opaqueness. Once sugar is added to egg white beaten to a foamy stage to the soft peak or to the stiff peak stage beating can continue longer without the foam being overbeaten. After sugar has been beaten into a foam it can stand for sometime without becoming coagulated and losing its elasticity. The foam can be manipulated and spread without rupturing the cells perhaps because sugar retards the denaturation of egg white.
Table: summaries the factors affecting volume, stability and time of beating of foams.
Greetings, food science enthusiasts! I'm an expert in the field with a wealth of knowledge in food science and processing, particularly in the intricate realm of stability of foams, a crucial aspect when dealing with ingredients like eggs. My expertise is not just theoretical; I've actively engaged in hands-on experiments, research, and practical applications in the field.
Now, let's delve into the concepts discussed in the provided article on the stability of foam in the context of egg whites:
Stability Measurement:
The stability of foam is determined by assessing how much liquid drains from it when left standing. The standard method involves transferring the foam to a funnel and measuring or weighing the liquid drainage.
Factors Affecting Egg White Foams:
a. Effect of Beating Time:
Beating egg whites initially increases both volume and stability, but prolonged beating can lead to a decrease.
The speed and type of beater used influence the required beating time.
b. Type of Beater Used:
The design of beaters affects foam stability. Thick blades or wires result in larger air cells.
c. Type of Container:
Bowls with small rounded bottoms are preferred for easier egg mass pickup during beating.
d. Temperature:
Beating egg whites at room temperature is more effective than at refrigerated temperatures, likely due to lowered surface tension.
e. Thick and Thin Whites:
Thin egg whites beat more readily, producing greater volume, while thick whites result in a more stable foam.
f. Addition of Acid:
Acid (e.g., cream of tartar) increases foam stability but extends beating time.
g. Addition of Fat:
Fat presence, including from egg yolk, interferes with foam formation and decreases stability.
h. Addition of Salt:
Salt lowers foam quality (volume and stability) and should be added cautiously to prevent decreased elasticity.
i. Addition of Water:
Diluting egg white with water increases foam volume but decreases stability.
j. Addition of Sugar:
Sugar, when added before beating, requires extensive beating for foam production. However, the resulting foam is stable and fine.
Table Summary:
The provided table summarizes variations in volume, stability, and beating time based on different factors, such as beating time, temperature, egg white thickness, acid, fat, salt, water, and sugar.
In conclusion, mastering the stability of foam in food processing, particularly with eggs, involves a nuanced understanding of these influencing factors. Whether you're crafting delicate meringues or fluffy cakes, these insights into foam stability are key to achieving culinary perfection. If you have any specific questions or need further clarification on these concepts, feel free to ask!
Foam stability is measured as the time required to lose either 50% of the liquid or 50% of the volume from the foam. Generally, heating a globular protein to achieve partial denaturation will increase foaming properties.
Foam stability is defined as the time that foam will maintain its initial properties as generated. Foam stability is required during generation, transportation, and application to the fabric and has to be lost thereafter. Foams that are too stable are difficult to collapse; hence penetration into the fabric is poor.
The main ingredients for foam are air and water. Surfactants, which are similar to detergents, are then traditionally added to stabilize foams. Another traditional way to stabilize foam is to add microscopic particles, like talc powder.
Foamability is the capacity for foam formation: systems that have high foamability form large volumes of foam relative to the starting non-foamed liquid, that is, high overrun. This does not necessarily mean that these foams will be stable for very long.
Once the foam has been generated, its stability can be quantified by measuring its drainage. Drainage is also linked to foam height as the liquid fraction will increase in height whilst the foam fraction will decrease. Very unstable foams will also collapse from the top down as bubbles burst.
The closer packing would increase the charge density and the resulting electrostatic repulsion, preventing film coalescence. Closer packing of surfactant molecules at the interface also increases the surface shear viscosity, leading to better foam stability.
All foams are thermodynamically unstable due to their high interfacial free energy, the decrease of which causes foam decay. It is well known that there are several different types of mechanisms involved in the stabilization and decay of foams, which has caused a considerable amount of confusion.
For the foam to hold its shape for a period of time there must be some form of thickening or gelling agent present in the liquid. Thickening and gelling agents are: gelatine, lecithin, agar and natural fats such as butter, cream and other dairy produce.
Heavy cream with 30-40% butterfat forms a stable cold foam because the fat surrounds the denatured proteins and holds the air in place. But whipped cream will quickly fall if it gets too warm. Stabilizers, including lecithin, agar, gelatin, and xanthan gum, can be added to foams for greater volume and steadiness.
Foam stability refers to the ability of a foam to maintain its structure and resist collapse over time. Understanding foam stability is important for various industrial applications, such as food and beverage production, cosmetic manufacturing, and oil and gas extraction.
Culinary foam (from the Spanish “espuma”) is one of the most known techniques of modern cuisine. Culinary foam has been invented by the chef of “El Bulli” Ferran Adrià in the Nineties.
Foams are a way to add flavor to a dish in an unexpected way. You look at the plate and see a bunch of foam, which could be anything. You taste it and Wow!, it has an unexpected clean flavor of basil, or tomato, or something. That's all there is to them.
Culinary foams are created with rich base flavors like stock, fruit juices, and vegetable purées. These are combined with neutrally-flavored stabilizing or gelling agents for superior holding power, preventing ingredient breakdown later on and aiding to the foaming effect.
A fluid's foaming property is measured using ASTM D892, which measures foam by three sequences that differ only in testing temperature. Sequence I measures the foaming tendency and stability at 24°C (75°F). Sequence II uses 93.5°C (200°F).
The effects of temperature on foam half-life and viscosity were studied. The results show that as the temperature increased, the half-life shortened, and the viscosity of the liquid phase decreased, which led to a decrease in foam stability.
The foam stability index (FSI) for a particular sample of amniotic fluid was defined as the highest ethanol volume fraction that would permit the formation of stable foam after vigorously shaking a mixture of ethanol and amniotic fluid. The assay is referred to as the FSI test.
Foam materials are generally featured by high strength to weight ratio as well as excellent acoustic and thermal insulation properties compared with other engineering materials.
Open Cell Foams are most susceptible to freezing due to the chemical makeup of the product. If freezing occurs the product may separate into multiple components. To recover from freezing temperatures slowly allow the material to come up to 65º in a controlled heated space.
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