Food freezing technology.

Technology is the technology of freezing food preserve food by lowering the temperature to below the freezing point of water. This is in contrast to thermal processing, in which the food is exposed to high temperatures and thermal stresses lead to food, can lead to the loss of nutrients, change in taste, texture, or chemical processing and fermentation can alter the physical and chemical properties of food. Frozen foods generally do not experience it all; freeze food tends to preserve the freshness of food. A consumer favorite frozen foods than canned or dried food, especially in the meat and dairy products, fruits, and vegetables.
Almost any type of food can be frozen for the purpose of preservation. This will cause the freezing of the water content in foods and cause a reduction in the activity of water in it. Decreasing temperature and water availability is the bottleneck of the disappearance of the major growth of microorganisms and enzyme activity in its food, causing the food to be more durable and not easily decompose. The advantages of the technique of freezing foods is all that can be achieved by maintaining the quality of the food as nutritional value, organoleptic properties, and others.

Food freezing technique has been known for a long time, while the technique of freezing the salt-ice mixture was introduced around 1800 in two places, namely in the United Kingdom and in the United States that they utilize to cool fish. Commercialization of new food freezing techniques began in the late 19th century.

Freezing point depression.
Freezing point is the temperature at which ice crystals and water are in a state of equilibrium; precise point at which water freezes or ice melts right. Pure water freezes at 0oC temperature at atmospheric pressure. Freezing the food was below freezing pure water, this is because the foods contain various mixtures of various substances and their interplay thus lowering the freezing point. Level freezing a food depends on the concentration of substances in food.

The freezing process.
When food is exposed to cold temperatures, food products will lose heat due to the rate of heat transfer that occurs from the food to the low temperature in the surrounding medium. The surface temperature of the food will decrease faster than the inside.
The amount of water that freezes in food products depends on the temperature of freezing; contains a mix of nutrients greatly affect it. Generally, the more liquid a food ingredient, the amount of water that will freeze more and more. However, the yolk still leaves more than 20 percent of the water though it is cooled to minus 40oC. This is because the high protein content that are dissolved in water. Lack freeze freezing technique is the difficulty of water content in the food perfectly so that still leaves the risk of growth of microorganisms; to overcome needed cooling further to stop the enzymatic activity of microorganisms and freeze more water, but it was not economical.

Phase change and the formation of ice crystals.
When the temperature is lowered food products to below the freezing point, the water begins to form ice crystals. The formation of ice crystals can be caused by a combination of water molecules called homogenik nucleation, or the formation of the core around the suspended particles known as heterogeneous nucleation. Homogeneous nucleation occurs in conditions in which the substance is free of impurities, which generally act as nuclei on freezing. Heterogeneous nucleation occurs when water molecules together with nucleating agents such as foreign bodies, insoluble substances, or even wall wrap. Heterogeneous nucleation is a common type that occurs in the process of freezing food.
The third type of nucleation process, which is called the formation of secondary nuclei, formed when crystals split. Type of crystallization provides a uniform crystal size, and is common on the freezing liquid foods.
Generally, the process of freezing food, the temperature decreases from the initial temperature above freezing to a few degrees below freezing. In this process, the temperature at 0 to-5oC called critical zones required by the food in the formation of ice crystals. The length of time it takes for food in through the critical zone is to determine the number and size of ice crystals formed. Rapid freezing process will form a large number of small ice crystals, whereas in a slow cooling will form a small number of large ice crystals. Freezing is slow to allow time for the water molecules to migrate to the nucleus to be united with it to form aggregates of ice crystals resulting in a large ice crystals. The formation of large ice crystals will affect the structure of the food and cause the loss of food quality. A large ice crystals pierce cell walls and damage food products. The damage will be even greater with the slow rate of freezing. The solution of these problems is to add anti-freeze proteins that can lower the freezing point of water and prevent crystallization at extremely low temperatures.

Estimated time of freezing.
All food products contain various types of solutes. It is very difficult to determine at what temperature throughout the water would freeze in food products, due to the presence of dissolved substances in the diet lowers the freezing point.
Cooling rate affect clotting time required quality food products food products can be defined by the difference between the initial temperature and the final temperature of food product freezing divided by time. Can also be defined as the ratio of the difference between surface temperature and the temperature inside the food product with the time needed to reach the surface of the food product to a temperature of 0 degrees C and the inside temperature of food products to reach -5 degrees C.
Estimated time of freezing is a major factor in making freezing food. When freezing to determine the capacity needed in the cooler to freeze.
Factors that influence the length of the freezing process is the thermal conductivity, specific heat, thickness, density, and surface area of ​​food products as well as the difference between the temperature of food products with a medium rate of cooling and heat transfer resistance. Estimated time of freezing the more difficult because the thermal conductivity, density, and specific heat of food products varies depending on the initial temperature, size, and shape of the food.
The bigger the size of the food product, the time required to perform the freezing takes longer. This is because the increase in latent heat and the amount of heat that must be removed. Increasing the size of food also increases the internal resistance of the heat transfer rate, thus requiring more time to freeze.

Tool freezing.
Type of equipment used for a particular product is determined by various factors. Sensitivity product, size, and shape as well as the quality of the final food product is required, the rate of production, availability of space, capacity investment, the type of cooling media used, and so on. Freezing equipment can generally be grouped as follows:
Utilizing direct contact with cold surfaces; food products, both packaged in a state or not exposed directly to cold surfaces, metal, plate, and so on.
Utilizing media air as the cooling medium; air in very cold temperatures used in cooling food products. Air blast, air spray, fluidized bed are also included in the method.
Using liquid as a coolant. In this case, the fluid temperature is very low, low boiling point and high thermal conductivity are used to cool the food product. The liquid is sprayed onto the product or the product soaked into the liquid. Included in this is the cryogenic method.

Direct contact with cold surfaces.
In the freezing cold plate system, the slab seems to be wrapping food products. Slabs can be either double plate or plates are cooled by a lot of different ways. Air space between the plates and wrappers can add resistance to heat transfer rate barrier, so that the space between the plates should be minimized to adjust the size of the food products. And that is the advantage of this method; shape and size of the plates can be adjusted to the size of food products. Another advantage is that freezing can be done quickly from all sides of food products, because metals have a high thermal conductivity so that the heat transfer can be sped up quickly.
Freezing with plates like these tend to save space for the location of the food preparation neat and structured.

Freezing air by utilizing media.
It is a common type of freezing, the cooling chamber filled with air cooled. The advantage is, to take advantage of the flow of convection, the cold temperatures can propagate efficiently into a corner, but the convective heat transfer coefficient of air tend to be small so that the freeze should be done in a longer time due to the low rate of heat transfer. The bigger the room, the smaller the heat that can be transferred in a given time unit. The loss of weight of the product can also result from direct contact between the product and the water is able to raise the water content in food products, especially if temperature and humidity allow.
Air circulation can be done naturally or mechanically by using a fan.

Freezing using liquid.
Generally, food products immersed in coolant cooled. The liquid used in the form of liquid that has a low boiling point but has the ability to absorb heat, such as glycol or other liquid called coolant. Food can also be cooled liquefied in this way as long as packaged before soaking. Generally there is no direct contact between food products with liquid cooling, because the risk of damaging the quality of food products.
Spraying food also includes methods, using similar coolant. The food supplied to the conveyor and spraying. After spraying, generally frozen food products with the use of media such as air drafts. This method makes the food to be frozen faster than without coolant.
With the cryogenic method, foods can be frozen in a fast way. Food soaked in liquid cryogen cryogenik called. Commonly used cryogen such as liquid nitrogen and liquid carbon dioxide. Liquid nitrogen has a very low boiling point, which is -196 degrees C, whereas liquid carbon dioxide has a boiling point of -79 degrees C. Cryogen tend odorless, colorless and inert so it will not react with solid food while cooling done in a state without affecting the quality of the food is packaged and except for cold temperature itself. In addition, the cryogen has a heat transfer rate is higher than the other coolant.
In the cryogenic freezing process, initial cooling is necessary to prevent cracking due to temperature drop dramatically because the volume of food products undergo the volume changes very quickly when submerged in the cryogen. Maintaining the temperature is very likely due to the vaporized cryogen has a convective heat transfer coefficient is very high.
Recent modifications of cryogenic cooling is a cooling method that combines cryomechanical immersion in liquid cryogen products and methods that use a mechanical sprayer type conveyors, spiral, or belt that utilizes cryogen vapor. This reduces the cooling time, reducing weight loss food products, improve product quality, and improve efficiency.

Effect of freezing and frozen storage of food.
Any addition or reduction of heat that made the food will bring some changes to the food. Cooling water will turn to ice, and the nature of the food will be determined by the nature of the ice. Growth of microorganisms and enzyme activity is determined by the reduced activity of water in frozen food. The number and size of the ice core is formed sufficiently affect the quality of the product in terms of the level of damage to the bacterial cell wall and also the network structure of food products. Losing weight and drying surfaces generally lack the quality that is not wanted. Storage and transport conditions, especially temperature fluctuations will affect the crystallization of ice and product quality.

Effects on physical characteristics.
When the water turned to ice, its volume increased 9% (water has the smallest volume at a temperature of 4 degrees C and increased in volume as the temperature decreased. If the food product contains a lot of water, then the same thing will happen, but the water content, temperature cooling, and the existence of spaces between cells greatly affect the volume change.
Cell damage may also occur due to cooling: this caused the movement of ice crystals or cell osmotic conditions. Meat products are not damaged by products of fruits and vegetables as fibrous structural owned meat is more elastic than the structure of the fruits and vegetables that tend to be rigid.
Weight loss due to cooling is also a problem because in addition to quality issues, it is also an economic issue when the product is sold by weight of the product. Products that are not packaged will experience greater weight loss due to moisture migration rate toward the lower pressure region due to direct contact with the cooling medium.
Cracking or the formation of cracks on the surface to the inside of the product can also occur, especially when the frozen food products by means immersed into a liquid cryogen cooling or freezing causes the formation of a layer on the surface of the food. This layer against an increase in the volume of that product will experience stress on the inside. If the frozen layer is formed quite brittle, cracks will occur. The nature of the product such as porosity, size, modulus of elasticity, density and so affects the occurrence of cracks. Density changes due to increased volume, and this can be handled with cooling in high pressure conditions.

The effect on the building blocks of food.
Cooling reduces the water activity in foods. Microorganisms can not grow under conditions of low water activity and temperatures below zero. Pathogenic organisms can not grow at temperatures below 5 degrees C, but other types of organisms have different response. Vegetative cells of yeast, fungi, and gram-negative bacteria will be destroyed at low temperatures, but the gram-positive bacteria and mold spores known to be affected by low temperatures. Protein denaturation will experience colder temperatures resulting in a change in the appearance of the product, but the nutritional value is not happening despite denaturation occurred during the weight is not reduced. Freezing does not affect the amount of vitamin A, B, D, and E, but the influencing vitamin C.

Freezing effect on the thermal properties of foods.
Knowledge of the thermal properties of food products needed in the design process of freezing and the equipment needed, including heat transfer capacity.
The eggs are not included because the water content in general each egg contains the same water content
The thermal conductivity of ice is 4 times the thermal conductivity of water (ice thermal conductivity is 2.24 W / m K, the thermal conductivity of water is 0.56 W / m K) so that the thermal conductivity of frozen food is generally 3-4 times greater than the foods that are not frozen. During the early stages of freezing, rapid increase in thermal conductivity. For a diet rich in fat content, thermal conductivity variation with temperature is negligible, but in the case of meat products, the orientation of the muscle fibers affect the thermal conductivity.
Specific heat of ice is only half of the specific heat of water. During the cooling period, specific heat food products declined. Measurement of specific heat is quite complicated because there are ongoing phase change from water to ice. Latent heat of food products can be estimated from the fraction of water present in the food. Thermal diffusivity of frozen food can be estimated from the density, specific heat, and thermal conductivity. Combined with data on the thermal conductivity and specific heat of ice to water, can be estimated that frozen food has a thermal diffusivity value 9-10 times greater than the food that is not frozen.

Development of freezing techniques.

Freezing at high pressure.
Conventional freezing methods, especially in the case of large-sized food, will cause the formation of large temperature gradients. The surface of the food product will accelerate clotting faster than the inside, so on the surface of the food will have a large number of small ice crystals, while the inside will have a small number of large ice crystals. This will lead to loss of product quality.
Conventional Freezing will also cause an increase in the volume of products and cause tissue damage. When freezing carried out at high pressure, an increase in volume can be prevented and between the surface and the inside of the food products will experience freezing in speed is not much different that the formation of ice crystals will homogeneously on the surface and the inside of the food products.

Dehydrofreezing.
Food freezing method is applied in particular to the foods that are high water. Food didehidrasikan to meet the required moisture content prior to being frozen. When a product such as fresh fruits and vegetables with high water kadari frozen, the main problem is the quality of the disturbing increase in volume due to the water content in it that can cause tissue damage. Partial dehydration can be done with conventional air drying or osmotic drying. Partial dehydration can provide a variety of benefits, including lower heat transfer load of food products, simplify and reduce the cost of storage, handling, and shipping.

Energy conservation in the freezing process.
Freezing is an activity with the use of energy-intensive. Cost-effectiveness of clotting activity depends on the cooling load of food products that determine the energy consumed freezer. Transfer heat at the beginning of the freezing process is the most difficult and time-consuming, so that the end point of freezing, which is generally difficult to determine, should be estimated precisely and so determine the total energy consumption freezer. Manipulation of the building blocks of food products, automation equipment cooling, tracking the phase change of water-ice, and so on, also be important in determining the total energy required in the freezing process as it prevents excessive heat transfer.