Principles of food storage
Any action that prolongs food storage is called canning or preserving food. Therefore, different methods of canning can be a simple heating operation, such as pasteurizing milk, or a series of complex and controlled operations, such as turning wheat into bread or freeze-drying.
The principles and preservation of food in all the above methods are based on three principles:
1- Eliminating microbes or preventing their activity;
2- Eliminating the effective factors in chemical interactions such as enzymes and oxygen or preventing the formation of chemical compounds;
3- Packaging to prevent re-contamination of food with microbes and effective factors in chemical interactions;
The following table classifies the different methods of food canning:
Table 1- Different methods of food storage
Food sample sample classification
Heat pasteurization (below 100) milk
Heat sterilization (above 100) of canned foods
Heat the potatoes
Electron irradiation of meat
Evaporation drying of fruits and vegetables
Biological camping of apples and potatoes
Chemicals Chemicals for juices and bread
Smoking and salting fish concentrate
Concentrate Concentrate juices and milk
Biological fermentation of yogurt, pickles and cheese
Refrigerate (above zero) fresh vegetables and fruits
Freezing Freezing (below zero) of vegetables, fruits and meat products
Refrigerator application
According to National Standard No. 4559, a cold store is a closed (moving) space in a fixed or moving place that has a cooling system or device.
The refrigeration or refrigeration industry is very widespread in our time that its applications can be briefly described in the following six groups:
1- Home refrigeration;
2. Commercial refrigeration;
3- Industrial refrigeration;
4. Transport refrigeration;
5- Air conditioning of buildings;
7. Industrial ventilation
Types of refrigerators
Refrigerators are divided into three main parts:
1- Short-term or temporary cold stores;
2- Long-term refrigerators;
3- Freezing cold stores.
In short-term and long-term refrigerators, the product is cooled and stored at temperatures above its freezing point, but in freezing refrigerators, the frozen product is stored at temperatures between 12 and 23 ° C.
Short-term or temporary storage is usually accompanied by gradual introduction of the product and rapid replacement, and depending on the type of product, storage time varies from one to two days to a week or more, but rarely exceeds 15 days.
Long-term storage is done in commercial storage warehouses (public cold stores). In this case, the storage time of the product depends on the type and input conditions of the product. The storage time of the product in these cold stores is from seven to ten days and for some sensitive products such as tomatoes, it is up to six or eight months. Time changes for resistant products such as onions or some smoked meats. If perishable food is to be stored for a long time, it should be frozen and refrigerated. Other methods must be used to maintain such products for a long time.
There are different types of refrigerators with different technical specifications for storing food and perishable goods, which are classified into three main groups:
1- Refrigerators above zero degrees
This type of facility is established for storing fruit for a certain period of time and keeps the product fresh at a temperature of 2 to 3 degrees above zero.
2. Refrigerator below zero
These cold storages store livestock products, fish and generally foodstuffs that need to be stored frozen for a long time.
3. Two-circuit cold storage
It is a combination of the two types above and its degree is adjusted depending on the product to be stored. Refrigerators are basically used in two ways. One is unit-dependent industries in manufacturing plants that store only specific and identical materials, and the second is independent refrigerators that adjust their schedule depending on the needs and food items that are delivered to them. In this way, sometimes they are given to the meat company or sometimes to the cooperative organization of the city and village or other users.
From another point of view, cold storages are divided into two types, fixed and mobile, which are defined as follows:
Mobile refrigerators: In addition to all the refrigeration machines mentioned, a number of refrigeration machines are made in different designs to store different products and special applications for transporting meat, poultry, milk, ice cream, florists and hospital refrigerators. And so on. These refrigerators are installed on vehicles such as trucks, trailers, vans, etc. and are used to transport materials, move them from one place to another or from the production site to the consumption center. In these refrigerators, Freon 22 gas is mainly used and their operating system is slightly different from the fixed refrigeration system.
Fixed refrigerators: Fixed refrigerators are a set of suitable buildings and facilities that can artificially provide special storage conditions for the product in terms of relative humidity and temperature, and if necessary have other specific conditions and can not be transferred. Fixed refrigerators are divided into five general categories:
1- Production cold storages: Storage of food and agricultural products is made for special goods or commodities, such as apple cold storage, meat cold storage, agricultural products cold storage, etc. The storage period of goods in these cold storages can last from two to nine months and their capacity is measured and determined by economic criteria.
2- Storage refrigerators: These refrigerators are built close to the place of consumption or production. The variety of goods in them is usually not great, the desired goods can be stored in this refrigerator close to the maximum storage time listed in the standard table. Annual arrivals and departures of goods in this cold storage are low.
3- Distributed cold storage: These cold stores are built in or near consumption centers and are used to distribute stored goods among wholesalers and meet the needs of the market, so the frequency of entry and exit and also the variety of goods in it is high.
4- Transit refrigeration: Foodstuffs are among the goods that can not stay in the customs for a long time for exit, because they are perishable and due to the short time of transporting them to the destination, the owner of the goods will be damaged. For this reason, in the customs points and places that are changed by transportation, in order to prevent losses, cold storages called transit cold storages will be constructed so that if the shipment is delayed, it can be kept in a safe and healthy place. Had. The entry and exit of goods in these cold stores are usually done in large quantities and the storage period of goods in them is short.
Dedicated refrigerators: These refrigerators are usually built near hotels, restaurants, supermarkets, hospitals and other low-consumption centers. The capacity of this type of cold storage is usually about 25 tons. Buildings, facilities and special storage conditions in this type of cold storage are not subject to standard regulations, but are required to comply with special regulations of the country’s legal authorities regarding the maintenance of food hygiene and storage.
– National standards
Refrigerators that are built to store food and to prevent spoilage of products should be built according to standards that can easily accommodate the products and prevent any damage to the stored materials. For this purpose, the Iranian Institute of Standards and Industrial Research has developed instructions for the construction of cold storage and how to store products in them. The total number of standards prepared is about 40, of which No. 1899-16 is related to the building regulations of the facility and technical equipment and maintenance of food refrigeration, No. 3589 is related to calculating the weight capacity of halls, No. 2720 is related to calculating the refrigeration load of food refrigeration and Other issues relate to the practice of preserving various fruits and vegetables, meat and protein products. In this work, the general criteria related to each of the titles have been stated and have been revised during the past years according to the scientific advances of the world.
Large fixed refrigerators must comply with the standards written for them and meet the specified standards. Therefore, before taking any action, the executor of the project should study the set standards and be fully aware of the actions related to the establishment and maintenance of the cold storage.
Table 2 – Related Iranian National Standards
Standard issue issue year ICS_Code
4559 Methods of storing fruits and vegetables in cold storage with controlled air 1998 01/080/67
830 Fruits and vegetables – Storage in the cold store – Ritual of work 2008 / 020,67 / 080
946 Rules of keeping apples in the cold store 1369 67/080/10
1899 Building Work Procedure – Equipment and Safety of Food Refrigeration 1996
1899-16 Building work procedure, facilities, technical equipment for health and maintenance of food cold storage 1370 91 / 91,040 / 140,
55/220
2199 Physical Conditions of Food Storage in Refrigeration – Definitions and Measurement 2008 27/27
Procedure for calculating the refrigeration load of food refrigeration
Procedure for picking goods in the food refrigerator
Procedure for calculating the weight capacity of food refrigeration storage halls 1374 27/200
4107 Procedure for delivering fruits after storage in the cold store
4559 Methods of storing fruits and vegetables in cold storage with controlled air 1998
4922 Procedures for preventing and combating ammonia gas leakage in cold stores 1378 27/27
6803 Fruits and vegetables – Storing kiwi in the cold storage – Ritual of work 1380/07/10
Preparation of fruits and vegetables
Cucumber
Cucumbers should be kept well for 10 to 14 days at a temperature between 45 and 50 degrees Fahrenheit. Temperatures below 45 ° C for more than two days can cause damage. Damaged cucumber cools soaking wet spots, burning peat or tissue. Extensive decay develops when removed from low temperatures. Temperatures above 50F cause the product to produce quickly and turn yellow after about 10 days. If cucumbers are stored with ethylene-producing goods, washing will be faster. Proper humidity is also important because cucumbers are at risk of losing moisture. They are used to help prevent dehydration.
Eggplant
Eggplants are extremely sensitive to temperature. They are best stored at 45 to 50 degrees Fahrenheit. Low temperatures cause damage. Bruising is a common problem that is not used when used carefully. The decay appears as dark brown spots on the surface.
Lettuce
The recommended storage temperature is 32 degrees Fahrenheit. Temperatures above 32F reduce the shelf life of lettuce. The temperature should be kept close to 32 degrees Fahrenheit. 38F storage temperature reduces storage life by half. However, lettuce is also easily damaged by freezing; Therefore, the storage room should be kept above the freezing point at 32 degrees Fahrenheit. Difficulty is also faced with rising temperatures. As the temperature rises, so does the rate of respiration, which shortens the shelf life. Lettuce leaves fry about twice as much as lettuce. If the temperature is kept below 35 degrees Fahrenheit, intestinal spotting is usually under control. However, ethylene-producing items such as apples, pears, and chickpeas can increase red spots. Source lettuce is more sensitive than other species, air circulation is important for lettuce. Lettuce should be stored to maximize blood circulation.
Melon
Melons should be stored at 50 degrees Fahrenheit. Melons are strongly affected by the intensity of very hot or very cold temperatures. You need to be careful when storing melons with other products. Table 46 Appendices shows the list of sensitive ethylene goods. The ethylene gas produced by melons can age some vegetables and can cause butter. Some of the required characteristics among different melons are:
Kasaba
Kasaba infertility is shown with yellow skin color and thickening at the end of the bloom (opposite the stem ulcer). The meat should be soft, creamy white, sweet and juicy.
Crenshaw
The melons are round at the base, reaching a point at the end of the stem. They have a golden and green skin that is smooth and unobtrusive and slightly belted. When ripe, they show softening of the skin at the large end, golden skin and flavor.
Honey
This color has a red and cream color and its color varies according to the origin. If the outer surface is white with a green tinge, it is unpleasant and low in sugar. A hard and smooth feeling on the skin also indicates immaturity.
Mushrooms
The best storage temperature is 32 degrees Fahrenheit. Even under optimal conditions, the fungi do not keep more than a week after harvest. At 32 degrees Fahrenheit, the mushrooms are kept in the initial conditions for five days, for two days at 40 degrees Fahrenheit, and for one day if the temperature reaches 50 degrees Fahrenheit. Due to the high rate of respiration, fungi need good blood circulation. Fungi are mainly composed of water (90%) and should be protected from dehydration. Do not put mushrooms in plastic bags. Do not wash mushrooms. Discard a large adult pod (more than 4) from the top.
Okra
Store 45-40 degrees Fahrenheit. Large discard (over 4) over mature pods.
Onions, pots
Onions should be stored in a dry dry place. Chopped onions can be stored at 32 degrees Fahrenheit to inhibit germination. The best onions will be hard and tough. They must be dried. They may need further drying after harvest to be well stored. 90 ° F with air circulation causes drying and drying.
Green onion
Green onions are very rotten and should be stored at 32 degrees Fahrenheit. High temperatures cause the leaves to turn yellow and fall off. Frozen is useful in providing moisture.
Pepper
Peppers should not be stored for more than 5 to 7 days under optimal conditions. The recommended temperature is 45 to 50 degrees Fahrenheit. Peppers will be damaged if they remain below 45 degrees Fahrenheit. Temperatures above 50 degrees Fahrenheit will encourage redness or the development of red color and the rapid growth of rot.
potato
Keep the store in a cool, dark place. Potatoes should not be cooled below 45 degrees Fahrenheit or transfer the starch to sugar to create a sweet flavor. Light is also a factor because even small amounts of light will cause green potatoes. Potatoes stored at 42 degrees Fahrenheit can be stored at 50 degrees Fahrenheit or slightly higher for a week to 10 days. It converts the sugar into natural starch and opens the scales, giving the potatoes a fresh taste.
Radish
Preferably stored at 32 degrees Fahrenheit. Like carrots, trained radishes are longer than prickly radishes.
Green Spinach
Store at high temperature 32 degrees Fahrenheit
Squash
For storage periods of less than four days, store the suction daily at 32 to 40 degrees Fahrenheit and use it immediately after harvest. If longer than four to five days, the temperature should be 45 to 50 degrees Fahrenheit. Storage life under optimal conditions usually takes two weeks to be of good quality.
Sweet corn
Sweet corn needs to cool down quickly after harvest. The use of hydraulic cooling or frying in an instant refrigerator at 32 ° F gives the best results in preventing sugars from turning into starch. Loss of sugar at 70 degrees Fahrenheit is 4 times faster than at 32 degrees Fahrenheit. Never leave enough sweet corn unless it is very frosty in terms of its tendency to heat through the candle. Maximum shelf life 4 to 8 days when stored properly.
sweet potato
Sweet potatoes should be stored at 80 to 85 degrees Fahrenheit and 90 to 95 percent relative humidity for 4 to 7 days before storage. After cooking, reduce the temperature to 50 to 60 degrees Fahrenheit. At low temperatures, sweet potatoes cause damage, decay, hard core and flexibility.
tomato
Tomatoes that are ripe green and properly harvested turn into a full-color product with a good flavor. The recommended temperature for reaching is between 50 and 70 degrees Fahrenheit. Tomatoes are exposed to cold damage at temperatures below 50 degrees Fahrenheit and quickly lose their flavor. Care is very important in handling. Stroke causes corruption and shortens life expectancy. Do not let it stay 50 degrees lower !!! The quality of tomatoes depends on proper harvesting and handling methods.
Watermelon
Keeping watermelon at room temperature for a few days can improve the flavor and color. At 50 degrees Fahrenheit and below watermelon loses color, neutralizes flavor and is crushed. At higher temperatures they tend to collapse. Immature melons do not ripen enough, when harvested, total sugar does not rise.
Sweating
When fruits or vegetables are harvested from a low temperature to a high temperature, the humidity often drops from the air to the cold surface of the product. This is known as sweat; The higher the relative humidity, the more pronounced it becomes. This is because the dew point of the air is at a higher or higher temperature than the product. Sweating, however, may be used to prevent or prevent it, especially with more cohesive onions and fruits, as it may cause destruction. This does not mean that when the products sweat after being removed from a frozen room, they decompose; This means that the conditions for degradation are more favorable, unless the surfaces remain until they are consumed. On the other hand, vegetables and greens can be heated gradually. The movement of air on the product while it is warming is useful in drying the surface.
Storage of composite goods
In some cases it may be necessary to manage different products together. This may or may not be. With some products there is a reciprocal transfer of odors. Also, some processed products, such as ethylene, are produced by some products that may be harmful to others. Ingredients that should be avoided in storage rooms are apples or pears with celery, cabbage, carrots, potatoes or onions. Melt celery with onions or carrots and citrus fruits with any of the intense vegetables. Table 45 in these diagrams shows the list of sensitive ethylene goods. When stored with potatoes, unpleasant pears and apples get the ground. It is recommended that onions, nuts, citrus fruits and potatoes be stored separately. Salads, carrots and vegetables when stored with apples, pears and many other fruits and some vegetables are damaged due to ethylene, which is produced from these products as a natural substance. Very low concentrations may have adverse effects. Ethylene also causes many fruits and vegetables to settle. This effect of sediment is low at low temperatures (for example, 32 degrees Fahrenheit), but may affect higher temperatures. For this reason, products such as cucumber, pepper and oak sakurah, in which green color is desirable and should be stored at 45 to 50 degrees Fahrenheit, should not be stored with apples, pears, tomatoes or other ethylene. Production of agricultural products such as crabs, melons Honey and tomatoes.
Simple ventilation of storage rooms is the cheapest way to remove excess ethylene, which ensures that the outside air is not polluted. Goods full of fine and rotten produce significant amounts of ethylene and must be regularly removed from storage. Internal combustion engines release some ethylene into their exhaust and should never be closed in a storage area. Goods that are very sensitive to ethylene should be used with electric forklifts
Several available materials directly absorb ethylene or convert it to inactive compounds. Absorbs certain types of activated charcoal or ethylene bromide; However, some cheaper materials use potassium permanganate to oxidize ethylene to plain carbon dioxide and water. Purafil is an example of a commercial attraction available.
Manipulating storage space, whether in large warehouses or in small packages, can reduce the harmful effects of ethylene. In general, reducing oxygen and increasing carbon dioxide is important for this purpose and is an acceptable commercial method for some products. Other chemicals that directly inhibit ethylene production or ethylene activity are not removed for post-harvest use in vegetables.
Sometimes it is necessary to store or transport different types of goods in a common area. For this to be successful, products must meet the same expected conditions. Items shipped in mixed loads must be compatible with the following:
Temperature means cold tolerance or sensitivity
relative humidity
Ethylene production rate
Sensitivity to ethylene
Discover products with odors
Absorb odor