Under canning It is customary to understand the method of food preservation (canning), which involves the technical processing of fresh raw materials in order to inhibit the vital activity of microorganisms that provoke its spoilage. In addition, canning also includes a number of some other methods that increase the shelf life of food.
Chemical preservation methods
Among the chemical methods of preservation used in the food industry, the most important is preservation with table salt, or salting. In addition, acetic acid, antiseptics, antioxidants, spices, and gases are used as canning chemicals.
Ambassador. The preservative properties of sodium chloride solutions are due to the action of sodium chloride on proteins, enzymes and microorganisms. When acting on proteins, Na + and C1 - ions, joining at the site of peptide bonds, block them, while protein molecules become resistant to the action of proteolytic enzymes. This effect is directly dependent on the concentration of salt in the cell sap.
Table salt inhibits and changes the nature of the biochemical activity of enzymes. In this regard, the proteolytic enzymes of microorganisms in the presence of salt form different products of protein cleavage than in its absence. High salt concentrations inhibit the biochemical activity of proteolytic enzymes. The vital activity of microorganisms is accompanied by an osmotic exchange between the cell and the environment. When the osmotic pressure of the solution surrounding the microbial cell is greater than the osmotic pressure of the plasma, an outflow of water from the plasma (plasmolysis) occurs, as a result of which normal metabolism is disrupted in the microbial cell.
Application of acetic acid. Fish preservation is achieved by the combined action of weak solutions of sodium chloride (6-18%) and acetic acid (0.3-2%). Acetic acid enhances the preservative effect of table salt, and table salt weakens the maceration of meat with acetic acid. The preservative effect of acetic acid is due to changes in the concentration of hydrogen ions and the toxic effect of undissociated molecules. For the vital activity of the overwhelming majority of microorganisms, the optimal pH values lie in the range of 6.5-7.5, therefore, a decrease in pH to 4.5-5.0 causes the death of such microorganisms. However, there are types of microorganisms that can develop even at pH 2.5-4.0.
Solutions containing 1-2% acetic acid inhibit the development of most putrefactive microorganisms, and at 5-6% concentration, almost all microbes die off, but spores remain viable. Mold resistant to acetic acid solutions: weak solutions encourage mold growth, and some molds grow in solutions containing as much as 10% acetic acid. Molds use acetic acid as a source of carbon, which leads to a decrease in acid concentration and allows the development of other types of microorganisms. The development of molds on the surface of marinades can be prevented by coating them with a layer of vegetable oil (excludes contact with air), as well as by using hermetic packaging.
The use of antiseptics. A number of chemicals have the ability to react with the protoplasm of a microbial cell and at the same time have a toxic effect: they paralyze the action of enzymes and cause the death of microbes; spores are more resistant to such action. Such substances are called antiseptics. The preservative effect of an antiseptic depends on its chemical nature, concentration, temperature conditions, pH of the medium. At a concentration of an antiseptic below the lethal, inhibition occurs, and at low concentrations even stimulation of the growth of microorganisms. An increase in temperature increases the toxicity of the antiseptic. However, if its concentration is insignificant, then with an increase in temperature, the protective effect of the antiseptic may be insufficient to protect products from spoilage. Antiseptics have a selective effect, therefore, the preservative effect of individual antiseptics depends both on the species composition of the microflora and on the number of microorganisms.
For the manufacture of food products, it is allowed to use urotropine, benzoic acid and its sodium salt (sodium benzoate), sorbic acid.
The use of antioxidants. Fat oxidation is a very significant defect that occurs during storage of frozen, salted, dried fish, fishmeal. The oxidation of unsaturated fatty acids that make up lipids is determined by the action of atmospheric oxygen and oxidizing enzymes (lipoxidases).
Oxidation can be delayed by the use of antioxidants, the action of which is due to the presence of labile hydrogen atoms in their molecule, therefore, when peroxides are formed, the antioxidant absorbs energy and stops the autoxidation reaction. The antioxidant effect is achieved both through the destruction of active peroxides and through the inactivation of oxidants contained in the product. The protective action of the antioxidant continues until its complete oxidation, after which the process of oxidation of the substrate (fat) continues.
Chemicals that stimulate the action of antioxidants, but do not have an antioxidant effect, are called synergists (citric acid).
The use of spices. In the manufacture of delicate lightly salted fish products with the addition of spices, the preservative effect of salt is somewhat enhanced by the action of essential oils contained in spices. The toxic effect of essential oils is different: the most toxic are allyl isothiocyanate (from mustard), eugenol (from cloves), cinnamic aldehyde (cinnamon). For example, mustard essential oil at a concentration of 0.2% is equivalent in bactericidal action to 0.031% sulfur dioxide.
gas storage. Changing the composition of the air surrounding the product has a significant impact on the vital activity of microflora. An increase in the content of CO 2 in the air inhibits the development of aerobic microorganisms, but does not affect the development of anaerobes. When the air contains 10-20% CO 2, the growth rate of various types of microorganisms decreases by 20-50%. The cessation of vital activity of molds and bacteria occurs when the content in the air is 40-50% CO2, however, in this case, the product acquires unpleasant organoleptic properties.
The activity of molds and microorganisms is actively inhibited by ozone: at negative temperatures, the presence of 0.0003-0.0005% ozone in the air effectively inhibits the growth of microorganisms, but the active oxidizing properties of ozone adversely affect fatty foods, causing rapid fat oxidation.
Gaseous sulfur dioxide and nitrogen trichloride are also used to suppress the vital activity of microflora. Sulfur dioxide is used to preserve fruits and vegetables harvested as a semi-finished product for subsequent processing, which ensures the destruction and removal of excess sulfur dioxide. In fresh fruits and berries, the content of sulfur dioxide should not exceed 0.15-0.2%, and in finished products - 0.002-0.010%.
Food preservation methods
Canning is the processing of food products for long-term preservation of their good quality in various ways that ensure the suppression and termination of biochemical processes occurring in products under the action of enzymes. Canning allows you to eliminate seasonality in the consumption of perishable products, expand the range of goods and increase their readiness for consumption. In addition, the use of certain preservation methods makes it possible to obtain products with other properties, i.e. essentially other goods.
There are physical, physico-chemical, biochemical and chemical methods of preservation.
Physical methods include preservation using low and high temperatures, filtration, radiant energy, ultrasound, ionizing treatment.
Let's consider these methods.
1. Low temperatures are used for cooling and freezing food.
Cooling is the lowering of the product temperature to the minimum (0-4 °C). When cooling, freezing of moisture in the product is not allowed. Cooling causes a slowdown in chemical and biochemical processes, the vital activity of microorganisms and contributes to an increase in the shelf life of goods. Chilled foods have an internal temperature of 0°C or slightly lower. At the same time, the products almost completely retain their nutrients, taste and aroma (milk is stored chilled for up to 24 hours, meat for 15–20 days, etc.).
The temperature at which the formation of ice crystals in the product begins is called cryoscopic. The cryoscopic temperature for eggs is -2.8 °C, for apples - from 1.7 to -2.8 °C, for fish - from -0.6 to -2 °C, for potatoes - from -1.2 to -1.6 °С, for milk it is -0.5 °С.
Products are stored not only in a chilled, but also in a supercooled state, as well as in a frozen form.
Freezing is the cooling of products to a temperature of -12 to -18 ° C and below, while most of the water turns into ice. As a result, unfavorable conditions for the development of microorganisms are created in the product, and the rate of biochemical processes is sharply reduced.
The quality of frozen products is preserved better with rapid freezing, which is carried out at a temperature of -24 ° C and below. However, the quality of frozen products in terms of taste and nutritional properties is inferior to chilled ones.
During rapid freezing, small ice crystals form in the product, which are evenly distributed and do not change the structure of the product. During defrosting, the formed moisture is completely bound by the product. In chilled and frozen products, microbiological and biochemical processes are significantly slowed down or suspended, vitamins are well preserved.
The freezing process is also used to achieve the following goals:
1) separation of moisture when concentrating liquid food products;
2) changes in the physical properties of products (hardness, brittleness, etc.) when preparing them for further technological operations;
3) freeze drying;
4) production of original food products and giving them specific taste and commercial qualities (ice cream, dumplings and other quick-frozen products).
The effect of freezing is achieved at a temperature in the center of the product -6 ° C and below. Frozen products are stored at a temperature not exceeding -18 °C.
A frozen product differs from a chilled one in a number of features and properties:
1) hardness - the result of the transformation of water into ice;
2) color brightness - the result of optical effects caused by ice crystallization;
3) a decrease in specific gravity - a consequence of the expansion of water during freezing;
4) change in thermodynamic characteristics (heat capacity, thermal conductivity, thermal diffusivity).
During freezing, in contrast to cooling, there is a partial redistribution of moisture, injury to the tissues of the product with ice crystals, and sometimes partial denaturation of the protein.
During the freezing of products, their shrinkage occurs. The moisture carried away by the air is deposited on the surface of the air coolers in the form of a “snow coat”. Almost no shrinkage occurs if the product is in a sealed container or package.
2. High temperatures are used for pasteurization and sterilization of products.
Pasteurization is the heating of a product to a temperature below 100 °C. During pasteurization, only vegetative microbial cells die. Therefore, pasteurization, although it lengthens the shelf life, does not guarantee their complete safety. The nutritional value of pasteurized products practically does not change, only vitamin C is partially destroyed.
Sterilization is the heating of a product at a temperature above 100 °C. Sterilization kills most microorganisms and their spores, and destroys enzymes. Therefore, sterilized products are stored for a long time. During sterilization, their taste and nutritional value is reduced, vitamins are destroyed.
Liquid and puree products are preserved using the aseptic method: the products are subjected to short-term high-temperature sterilization in large containers, and then packed in sterile containers and sealed under aseptic conditions. At the same time, the heat treatment time of the product is reduced, as a result, its quality is better preserved after sterilization and during subsequent storage.
The products are also sterilized by ultra-high frequency electric current and ultrasound. Bactericidal properties are possessed by ultraviolet rays, which sterilize the surfaces of products, water, air, containers and equipment. Ultrasound destroys microorganisms and their spores. Mechanical sterilization - filtration of liquid products (fruit juices) through special filters that trap microorganisms. Irradiation with ionizing radiation can be used to delay the germination of potatoes, onions during storage, etc. This method is under development.
Physical and chemical methods are the preservation of products with table salt, sugar and drying.
Preservative factors are an increase in osmotic pressure (i.e. pressure caused by solute molecules) and a decrease in water activity. An increase in osmotic pressure is achieved by adding table salt or sugar to the product, or by concentrating the solutes of the product itself by drying it. At high osmotic pressure, water activity decreases, plasmolysis (dehydration) of microbial cells occurs, and enzymes are inactivated. The preservative effect of table salt is also due to the fact that active sodium cations and chlorine anions are attached at the site of peptide bonds of protein molecules, as a result of which the proteins of the product become unavailable for microbial nutrition.
1. When preserving by drying (dehydration), the moisture necessary for the life and activity of microorganisms is usually removed from the products by a thermal method. The most common drying of products with air heated to 80-120 ° C and above. For each type of product, optimal drying modes have been developed.
There is natural and artificial drying. Apricots, grapes and other fruits are dried in a natural way. Artificial drying of products is carried out in special drying chambers and apparatuses. Many drying methods are known: air heated to 80–120 °C (convective, spray), hot surface (roller drying), sublimation, vacuum, microwave and other types.
Vacuum drying is characterized by the fact that the product is dried without access to air at a relatively low temperature (40-60 ° C), due to which the original properties of the product are well preserved.
Microwave drying is carried out using microwave energy; the drying process is accelerated, the products acquire a porous structure, increase in volume.
When drying by sublimation, the product is dehydrated in a frozen state (at –5 °C and below) and under high vacuum (1.5–2.0 hPa). Under these conditions, the moisture of the product from the solid state (ice) passes into the vapor state, bypassing the liquid phase. Sublimation occurs, i.e. sublimation, frozen moisture into steam. Dried products quickly restore their original properties when pouring them with warm water. Sublimation is used to preserve meat, fruits, vegetables, juices and other products.
Dry canning has its advantages and disadvantages. The advantages are that dried products are well preserved, convenient for transportation, and have a higher calorie content.
The disadvantages of drying include a change in the physical state of the product (appearance, shape, volume, density), loss of vitamins, aromatic and flavoring substances. The size of the losses, and hence the nutritional value of the products, largely depend on the type of drying used. The most significant losses are observed in products during solar drying, drying with a hot surface and heated air.
2. Preservation with salt is used to suppress or terminate the vital activity of microorganisms as a result of an increase in osmotic pressure in the product when salt is added to it. High osmotic pressure causes dehydration and plasmolysis of the microbial cell. The preservative effect depends on the concentration of the cell.
When salting, there is a partial loss of the nutrients of the product, which, together with water, pass into brine, the taste properties change. Some types of fish (herring, salmon) as a result of exposure to salting acquire special taste qualities.
3. Preservation with sugar is also based on an increase in osmotic pressure, which suppresses the development of microorganisms in the product when sugar is added to it. The preservative effect of sugar is weaker than that of salt; therefore, preservation with sugar is often combined with pasteurization or sterilization of the product in sealed containers, as well as cooking. These methods are used to prepare jam, jam, jam, candied fruit. Products preserved with sugar have a higher calorie content compared to the original raw materials, however, when heated, vitamins and aromatic substances may be lost.
Biochemical methods of preservation. These methods are based on the suppression of the action of microorganisms and enzymes by adding preservative substances to products or their formation as a result of biochemical (enzymatic) processes. A typical example of a biochemical preservation method is fermentation.
Fermentation is based on the preservative effect of lactic acid, which is formed as a result of lactic acid fermentation of sugars in the product. The accumulated lactic acid, changing the acidity of the medium, suppresses the activity of putrefactive microorganisms, which explains the good preservation of fermented products in refrigerated rooms. Simultaneously with the formation of lactic acid, ethyl alcohol accumulates, which also has a preservative effect.
Fermentation is used for preserving vegetables (sauerkraut, pickled cucumbers, tomatoes, etc.), fruits, mushrooms. Fermentation, salting and urinating are different names for the same canning method. Salt added to products during fermentation plays the role of a flavor component, promotes the release of cell sap containing sugar, and also favorably affects the development of lactic acid bacteria in the first stage of fermentation.
The advantage of fermentation is that it allows you to get a product with different taste properties, as well as retain a significant amount of vitamin C.
Chemical methods. Chemical methods include the following methods:
1. Preservation with ethyl alcohol (based on the destructive effect of alcohol on microorganisms). At concentrations of 12–16%, ethyl alcohol slows down the development of microflora, and at 18% it completely suppresses it. Ethyl alcohol is used as a preservative in the production of fruit and berry juice semi-finished products, it causes long-term storage of wine and other alcoholic beverages.
2. Pickling (based on the suppression of the vital activity of microorganisms by acetic acid, which, like lactic acid, increases the active acidity of the medium). Acetic acid in an amount of 0.6 to 1.2% is added when pickling fruits, vegetables, fish, mushrooms. A small concentration of acid cannot fully guarantee the protection of the product from spoilage during storage. Therefore, fruits and vegetables marinated with a small amount of acetic acid are subjected to pasteurization or sterilization, marinating fish is combined with salting. A higher concentration of acetic acid worsens the taste of the product and is not harmless to the human body.
3. In addition to the listed acids, sorbic, citric, benzoic acids and their salts are used for preservation. The most promising of them is sorbic acid, which has a bactericidal effect on yeasts and molds. Unlike other chemical preservatives, sorbic acid does not have a harmful effect on the human body and does not impart any taste or smell to products. Sorbic acid and its salts are used for preserving fruit purees, juices, tomato products, etc.
Many other chemicals are known to be used to extend the shelf life of food products. Such substances include potassium metabisulfite, sulfur dioxide, urotropine, boric acid, etc.
Developers of biopreservatives are faced with a serious challenge. Due to the increase in the cost of metal containers, it has now become possible to use polymer containers for food preservation. But the disadvantage of this type of material is a decrease in the shelf life of the product. Therefore, they resort to various preservatives that can have an adverse effect on the human body. Among modern and fairly safe preservatives, preparations of natural origin should be distinguished.
Products of natural origin include products with the addition of bifidum and lactobacilli. Lactococci, which have beneficial properties for humans, are also used. The representative of this group is nisin - an antimicrobial substance of natural origin. This is its difference from traditional and not at all harmless acetic, benzoic, sorbic acids. It is the only antibiotic approved by the health authorities for widespread use in the food industry.
Given the need for high-quality canned food with high organoleptic characteristics, the food industry, especially the canning industry, is beginning to introduce biopreservatives that have a high consumer value.
Combined preservation methods. They are widely used in the production and storage of food products. These include, for example, smoking fish, meat products. The preservative factors during smoking are chemicals that pass into the product from smoke or smoking liquid, partial dehydration of the product, and salt. Cold smoked goods can be stored at normal temperature for several months. Combined methods should also include drying fish (salting is combined with drying), obtaining canned milk (condensation is combined with sugar or sterilization).
Combined preservation methods often produce positive results in preserving the nutritional value of the product and improving shelf life.
Sanitary examination of canned food
Such examinations are carried out to assess the quality and safety of canned food. For processing into meat (poultry, fish, dairy) canned food, appropriate raw materials that have passed a veterinary and sanitary inspection are allowed. Before sterilization, the contents of cans are examined microbiologically. Ready-made canned food is subjected to organoleptic testing and laboratory research to determine the physico-chemical and microbiological parameters. Sampling of canned food and preparing them for laboratory studies for compliance with safety requirements for microbiological indicators is carried out after inspection and sanitization, checking for tightness, thermostatting canned food, determining the appearance of canned food after thermostating.
In accordance with the current standard, a unified system for marking cans with various canned products (mainly on tin cans) has been adopted. Marking in the form of an alphanumeric code represents the passport of a can of canned food. In addition, the jar indicates the date of manufacture of canned food and the shift that made them. Typically, markings are stamped or applied with indelible paint on the lids of metal cans.
The contact of a metal container with the contents often leads to undesirable chemical interactions - corrosion on the surface of tin and tin. These phenomena are more pronounced in canned foods with high acidity (marinades, vegetable snacks, etc.). In jars with canned food from products containing a lot of protein substances (meat, fish, peas, etc.), the so-called marbling, or sulfide corrosion, is usually formed when tin and tin iron interact with the sulfur components of protein products. This sulfide strong bluish-brown film is not harmful to health, but it detracts from the appearance of the product. To prevent corrosion and marbling, cans are made from pre-lacquered sheet metal (tinplate, aluminum and its alloys), and sometimes finished cans are varnished from the inside with food varnishes by spraying.
The main types of marriage of canned food include:
1) true bombing (swelling of lids and bottoms due to gas formation as a result of the vital activity of microorganisms with insufficient sterilization - biological bombing, or when the acids of the product interact with metal in unlacquered cans - chemical bombing);
2) false bombing (with excessive filling of cans, heating or freezing);
3) deformation of cans (crackers, birds);
4) rusting.
The optimal storage conditions for canned food are temperatures from 0 to 20 ° C, relative air humidity not higher than 75% (for jam, jams and marmalade to avoid sugaring - from 15 ° C) in ordinary storage facilities for long periods (usually several years). Preserves should be stored at low temperatures (below 0°C).
The microbiological indicators of safety (industrial sterility) of full canned food (groups A, B, C and D) include:
Spore-forming mesophilic aerobic and facultative anaerobic microorganisms of the B. subtilis group;
Spore-forming mesophilic aerobic and facultative anaerobic microorganisms of the B. cereus and B. polymyxa groups;
mesophilic clostridia;
Non-spore-forming microorganisms, lactic acid microorganisms, molds, yeasts;
Spore-forming thermophilic anaerobes, aerobic and facultative anaerobic microorganisms.
Microbiological safety indicators of incomplete canned foods include: QMAFAnM, BGKP, sulfite-reducing clostridia, salmonella, B. cereus, S. aureus.
From the point of view of chemical safety in canned products, the content of tin and chromium (for canned food in combined tin and chrome containers), degradation products of polymeric and other synthetic materials (depending on the class of polymer used), concentrations of used food additives (preservatives).
They need to be preserved!
As you know, we only get to enjoy fresh fruits and vegetables from our garden or from the market for only a few months a year. Therefore, it is so important to preserve this fruit, berry and vegetable abundance for a longer period. How to do it? The answer is simple: they need to be CANNED!
preserve, i.e. That is, it is possible to subject products to special processing and create conditions for protecting them from spoilage in different ways.
Pickling
Salting
fermentation
Freeze
Harvesting jams, jams, marmalade, jelly
- all these are ways of canning!
Using the recipes from our book, you can provide the whole family with vegetables and fruits prepared by your own hands. Now the crop is not only harvested, but also safely stored!
The use of canned foods in winter and spring allows you to diversify your diet during this period of the year, when the range of fresh vegetables and fruits is limited, which makes it possible to provide a balanced diet all year round.
If you are looking for new recipes for canned food, then you have a huge selection of ways to prepare a wide variety of preparations from a wide variety of products. There are recipes here for super lazy people, when the cooking time is about half an hour, lazy people (you will spend one hour) and for those who are not too lazy to cook yummy for the winter. Add your recipe to the collection!
The main methods of preserving food
There are several ways to preserve food: drying, salting, pickling, pickling, boiling with sugar, cooling, freezing, sterilization, etc.
Drying is one of the long-known methods of food preservation. It consists in the almost complete removal of moisture from the product.
Preservation of vegetables by salting and fermentation is based on the preservative effect of lactic acid in the presence of table salt. The latter significantly reduces the development and activity of unwanted bacteria and promotes the vital activity of lactic acid bacteria, which form lactic acid.
When urinating, sugar is added to the product to ensure the rapid accumulation of lactic acid. Salt is not added in this case. The most favorable temperature for the development of lactic acid bacteria is 15–22 °C.
Preservation of fresh fruits and vegetables using acetic acid is called pickling.
Fresh berries and fruits can be preserved in highly concentrated sugar solutions (jam, jam, marmalade, jelly, etc.). The preservative effect of sugar is manifested when its concentration in jam is at least 65%, in marmalade - at least 60%, in candied fruits - at least 75-80%. If the sugar concentration is lower, canned food should be sterilized or pasteurized, followed by hermetic sealing.
Cooling food products to a temperature close to 0 ° C ensures their safety for a long time. However, many microorganisms are resistant to even lower temperatures. To create unfavorable conditions for the development and vital activity of microorganisms, to suspend the activity of enzymes, and, consequently, the physicochemical changes in the tissues of food products, it is enough to bring the temperature of the canned product to -18 ° C. At this temperature, the quality of products does not change for a long time.
The nutritional value of frozen fruits and vegetables, i.e. their carbohydrate, protein and mineral content, remains unchanged. Vitamins are almost completely preserved. Even the least stable vitamin C in quick-frozen fruits and vegetables is quite stable.
Prevent spoilage of canned food
The main cause of food spoilage is the development and action of various undesirable microorganisms in them, therefore one of the conditions for ensuring the high quality of home-made canned food is cleanliness.
The room in which products are processed, utensils, containers, tools and fixtures used in this must be clean.
One of the main requirements that must be met when preserving food is the exact dosage of the ingredients of the recipe. For the convenience of dosing liquid and bulk components, you can use the data in the table. Using this table, you can easily measure the right amount by weight, using a glass or a tablespoon, which you always have at hand.
The time indicated in the recipes for boiling, additional boiling, sterilization and pasteurization is counted from the moment the water boils.
Before canning, raw materials must be carefully sorted out, selected according to size, maturity and color.
To prevent spoilage of canned food, you must:
wash food thoroughly before canning;
strictly observe the canning technology, especially the time of sterilization or pasteurization;
ensure the tightness of the closure;
observe the temperature regime during storage.
In the process of preparing many canned food, calcined sunflower or cottonseed oil is used. It is obtained by heating until white smoke appears (temperature about 160 ° C).
Marinating products
Preservation of fresh fruits and vegetables using acetic acid is called pickling. Pickling is one of the main methods of canning.
The food industry prepares acetic acid of 5-, 6- and 9% concentration, as well as acetic essence of 70-80% concentration.
If there is a 5% solution of acetic acid, and the essence of 80% concentration is indicated in the recipe, then a recalculation can be made.
Let in the recipe the need for acetic acid of 80% concentration is 30 g, then the amount of 5% solution of acetic acid to replace the specified amount of essence will be 30 * 80 / 5 = 480 g.
Technology for making jam, jam, marmalade, jelly
Fresh berries and fruits can be preserved in highly concentrated sugar solutions (jam, jam, marmalade, jelly, etc.). The preservative effect of sugar is manifested when its concentration in jam is at least 65%, in jam - at least 60%, in candied fruits - at least 75-80%. If the sugar concentration is lower, canned food should be sterilized or pasteurized, followed by hermetic sealing.
Jam, jam, jelly, jam must be cooked until fully cooked.
The readiness of jam can be determined by the following signs:
intensive foaming stops and with the same force of fire, the mass begins to boil more slowly;
the foam is collected in the center of the container in which the jam is cooked, and does not diverge at the edges, the berries do not float, but are evenly distributed in the syrup;
a drop of syrup dropped onto a glass or saucer does not blur when cooled.
The boiling point of the jam at the end of cooking during subsequent hermetic closure should be about 105 °C, and when stored without hermetic closure - about 108 °C.
The readiness of the jam is determined a small sample on a saucer. If sugar syrup does not separate from the boiled sample, the jam is ready for packaging.
To determine the readiness of jelly a drop of boiling product is dipped into a glass of cold water. If it does not dissolve, but sinks to the bottom, the jelly is ready. You can also put a drop of jelly on blotting paper. It is considered ready if there is no wet spot on the paper.
The readiness of jam is determined test on glass or plate. If the boiled mass does not spread, the jam is ready.
Ready-made jam, jam, jelly and marmalade in most cases are hermetically sealed. They can be stored without hermetic sealing, but the storage time is reduced.
Sugar syrup in canning
For 1 kg of all canned food, from all products, except for citrus peels, 1 liter of sugar syrup is prepared (the fact is that a kilogram of citrus peels is not covered with the indicated amount of syrup, so 1.5 liters of syrup are prepared for 1 kg of them). If citrus peels are cut into small slices, 1 liter of syrup is enough for 1 kg of slices, but then the appearance of canned food, especially candied fruits, is lost.
It is desirable to prepare sugar syrup in water, in which the products to be preserved were blanched.
Sugar syrup should be clean and clear. If after filtration it remains cloudy, it is clarified. For clarification of sugar syrup it is cooled to a temperature of 45-50 ° C and well-beaten egg white is added, the mixture is thoroughly mixed and brought to a boil.
The foam from the surface of the syrup is removed with a slotted spoon, and the hot clarified syrup is filtered through 3-4 layers of gauze. For 5 liters of syrup, 1/4–1/5 hours of protein of one egg is required.
All canned food prepared with sugar can be prepared for diabetics, but the sugar is replaced with sorbitol or xylitol. Besides, canned foods for diabetics you need to cook from unripe fruits, which contain less sugar. The concentration of syrup for compotes should be 15–20% (185 g of sorbitol or 250 g of xylitol per 1 liter of water).
Tools and fixtures for canning
The following utensils, tools and appliances are commonly used in the canning process:
stainless steel knife;
knife for peeling fruits;
device for removing pits from cherries and sweet cherries;
a pan with a blanching net (you can use a juicer grate);
tongs for removing jars from the sterilizer;
stainless steel or nickel-plated tongs for removing sterilized caps;
kitchen scales;
enameled pots and basins;
sieve (hair or stainless steel);
seaming machine (sealing key);
kitchen boards;
a wooden or metal grate placed on the bottom of the sterilizer;
thermometer with scale up to 150 °С;
juicer or press;
juicer.
The need for a particular tool is determined by the specifics of the recipe and the characteristics of the product to be preserved.
Canning containers
For canning fruits and vegetables at home, glass containers (jars) are usually used. Individual products can be preserved in barrels and bottles, but in this case it is difficult to ensure tightness when capping.
Canning jars come in capacities of 0.5, 1, 1.5, 2 and 3 liters. The outer diameter of the neck of the jar is standard and equal to 83 mm.
Glass containers for canning must be intact, without cracks. The integrity of the container is determined by lightly tapping it with a stick or pencil. If there is even an imperceptible crack, the sound will be deaf and rattling. It is also necessary to ensure that there is no chipped rim or ledge on the neck of the glass container.
Before canning jars are thoroughly washed. To do this, they are soaked in a solution of soda ash (1 teaspoon of soda per 1 liter of water) for 30 minutes or more, depending on the pollution. After that, the jars are rinsed with cold water and washed with a washcloth or hair ruff with soap or baking soda.
Secondarily, the jars are rinsed with clean (preferably hot) water and placed with the neck down to drain the water.
Before filling the jars with prepared products steam sterilized. It is convenient to sterilize jars with a capacity of 0.5–1 l in a teapot with a neck slightly larger than the diameter of the neck of the jar. Banks with a capacity of 2-3 liters are more convenient to sterilize in a coffee pot. Also, for sterilization of jars, a pan with a special lid for sterilization is used, which is a circle with a hole in the middle.
Converting the volume of products to mass
Recipes often give a mass of products, but there are no kitchen scales. Using this table, you can easily measure the right amount by weight, using a glass or a tablespoon, which you always have at hand.
Approximate content of spices in 1 g: black bitter pepper - 30 peas, allspice - 15 peas, cloves - 12 pcs., Bay leaf - 7 pcs. The mass of one clove of garlic of medium size is approximately 2 g.
Washing and packing products
Before canning, the products are thoroughly washed with running cold water. In some cases, contaminated products (such as root vegetables) are pre-soaked and then washed.
After washing, be sure to let the water drain, and in the case of preparing some types of canned food, the washed products are dried.
Before packing canned food, jars must be washed well with hot water and treated with steam or boiling water. If they are filled with jam, jam or marmalade, then before filling clean jars should be dried well in the oven, preventing them from becoming contaminated. When packing products in wet cans, canned food may become moldy.
Prepared products are placed in containers in bulk or in rows. When preparing fruit mixtures, fruits of light colors should not be stacked with fruits that give an intense color (cherries and apples, cherries and apricots, etc.), as such canned food will not have an attractive appearance.
When preparing compotes or marinades, fruits and vegetables packed in jars are recommended to be poured with hot sugar syrup, marinade and tomato fillings (temperature 85–95 ° C).
When packing, it is recommended to fill the container to the top (with the exception of cases specially specified in the recipe). If not the entire volume of the container is filled, then in its upper part there remains a layer of air containing up to 21% oxygen, which adversely affects many substances that make up the canned product (they quickly oxidize and lose their valuable properties). Therefore, the packing of the fruit should be tight, but not too tight, as this can cause bruising of the fruit.
Blanching
Blanching (blanching) consists in preliminary processing of fruits in hot or boiling water, followed by cooling in cold water. Most fruits and vegetables are blanched before canning.
* Plums are blanched in boiling water so that invisible cracks (mesh) form on the skin, which protect the fruit from boiling and cracking.
* Squash, white cabbage are blanched to give them elasticity and preserve their natural color, eggplant and pepper - to remove excess bitterness.
* When blanching apples, pears, quince, the fruit tissue softens, the color improves and the quality of canned food increases.
*Blanching of fruits, depending on their type, degree of maturity and size of fruits, lasts from a few seconds to 1 hour from the moment the water boils.
*After blanching, the products are removed from boiling water and immediately cooled under running water. Such processing helps to strengthen the fabric, displace air from the product, as a result of which it does not boil soft during further heat treatment.
* For blanching, at least 1 liter of water is taken for 500 g of food. Recipes usually provide detailed blanching recommendations for specific foods.
Roasting, sautéing and stewing food
Roasting, sautéing and stewing are used in the preparation of various canned snacks, vegetable preparations and other products.
Prepared vegetables (zucchini, eggplant, onions, carrots, white parsnips, celery, parsley) are fried in refined sunflower or cottonseed oil calcined until white smoke appears.
The purpose of frying is to remove moisture, give the products a specific bite and aroma, as well as increase calorie content by removing moisture and absorbing the oil on which they were fried by vegetables.
Passer products with the addition of fat, and stew in their own juice, that is, in the liquid released from the raw material during its maturation.
The duration of frying depends on the type and size of the pieces of chopped vegetables, as well as on the temperature at which the products are frying. Typically, recipes indicate the recommended size of the pieces, the temperature and duration of frying, sautéing or stewing.
Some types of fruit raw materials (apples, quinces, eggplants, peppers) are baked over intense heat to make them soft. Roasting fruits is usually done in a double-bottom saucepan, and vegetables in a baking sheet or pan.
Pasteurization
Pasteurization - This is a type of processing of canned food, which is the destruction of microorganisms by heating foodstuffs to a temperature below 100 ° C.
Some types of canned food made from berries, fruits and vegetables (compotes from apricots, grapes, pickled or canned cucumbers, squash, small-fruited tomatoes, etc.) during sterilization at 100 ° C are boiled for even a short time, their taste is reduced .
Therefore, during the canning process, these products are subjected to pasteurization, which is carried out at a temperature of 85-90 ° C. The time of such processing is longer than the time of sterilization.
The sterilization time is counted from the moment the water boils when the cans are immersed in it, and the pasteurization time is counted from the moment the set water temperature is reached.
During the heat treatment of canned food according to the pasteurization method, it is necessary:
use only fresh sorted and thoroughly washed fruits or berries;
strictly adhere to the temperature and time of pasteurization;
Thoroughly wash and boil the container before laying. Sterilization
To destroy microorganisms in canned foods, the latter are sterilized. Prepared fruits or vegetables are placed in glass containers, poured with hot sugar syrup, marinade or tomato sauce, covered with boiled metal lids and placed in a sterilizer with hot water.
As sterilizer you can use a basin, pan, bucket. A wooden or metal grate of the appropriate size is placed on the bottom of the sterilizer. It is not recommended to replace the grille with a piece of cloth.
The temperature of the water in the sterilizer should be 15–20 °C higher than the temperature inside the glass container, and the water level in it should be no more than 3 cm below the upper edge of the jar. There should be a gap between the jars and the wall of the container in which the treatment is carried out. at least 5–10 mm.
During sterilization, water should not be allowed to boil violently. Banks to be sterilized with subsequent hermetic sealing with metal lids should be hermetically sealed before processing it is forbidden, since excess pressure is formed in them during heating and the covers are torn off.
For some products, re-sterilization.
Steam sterilization produced in the same container as when sterilizing canned food in boiling water. At the same time, the amount of water in the sterilizer should not exceed the height of a wooden or metal grate.
When heated, the water boils and the resulting steam heats the jars and the contents in them. To prevent the steam from escaping, the sterilizer is tightly covered with a lid. The steam sterilization time for canned food is almost twice the time for canned food sterilization in boiling water.
Self-sterilization and re-sterilization
Canned food that is packaged in a hot (boiling) state and immediately hermetically sealed should be turned upside down and cooled. This type of conservation is called self-sterilization.
To guarantee the sterility of such canned food, it is necessary to prepare (scald) the containers, pack the product and seal the cans quickly and carefully.
Corked canned food is placed in a place where there is no draft, and covered with a thick cloth (blanket, towels) to keep the heat inside the jars longer.
Repeated (multiple) sterilization from two to three times the same can of canned food is produced at the boiling point of water and is used in the sterilization of food products containing large amounts of protein (green peas, meat, poultry, fish).
The first sterilization kills mold, yeast and germs. During the daily exposure in canned food after the first sterilization, the remaining spore forms of microorganisms germinate into vegetative ones and are destroyed during secondary sterilization. In some cases, canned food is re-sterilized after knocking for the third time.
Sealing and cooling
Hermetic closure. At the end of sterilization or pasteurization, glass jars are carefully removed from the sterilizer so as not to slightly open the lid and immediately hermetically sealed using a rolling machine.
To remove the jar from the sterilizer, it is convenient to use special tongs. If these are not available, you can use a clean towel.
Cooling. After sterilization or pasteurization and hermetic sealing, the jars are usually air-cooled.
Some types of canned food (apricot compote, canned or pickled cucumbers, tomatoes, white cabbage, quince and pear puree) should be cooled as quickly as possible after sterilization and capping so that the products do not soften and lose their natural color.
In this case, the jars are placed outdoors (in the yard) or in a cold pantry, but not in a draught.
It is possible, after hermetic sealing, to place the cans neck down in a container with hot water, where they were sterilized, and then gradually add cold water to the hot water so that the temperature of the contents of the cans gradually drops to 35-40 ° C, and then finally cool the canned food in air.
To date, it is not possible to name all the available methods for processing products of various types for their long-term storage. The microflora can be destroyed in different ways, leaving the product suitable for human consumption only.
Different nationalities and peoples have their own ways of preserving food, in addition, they differ depending on personal preferences and the products themselves. Each housewife has secret ingredients (marinades and spices) that are added to a jar of cucumbers or tomatoes before they are sent for storage. However, with all the arsenal of canning methods, they can be divided into main groups, which we will discuss in more detail.
Canned Food Types
Various canning methods are designed to remove moisture, which destroys a favorable breeding ground for bacteria, and products can have a longer shelf life or be filled with microbes, but still remain edible for humans. We will analyze each of the known methods.
- Drying. The method is used for certain types of vegetables, fruits, fish or meat. The essence of the method is that a special apparatus for drying or the sun's rays manage to remove moisture from the products before the bacteria begin their offensive.
- Salting. Products, more often meat or fish, are abundantly rubbed with salt, which removes liquid, depriving bacteria of their usual habitat.
- Pickling. As a result of this method, products are saturated with acetic, lactic or citric acid. For humans, these substances in small concentrations are harmless, but bacteria cannot multiply in them.
- Fermentation. This type of preservation is used mainly for dairy products, sometimes for some vegetables. The principle of operation is similar to the previous method, only canned foods are saturated with special bacteria - lactic acid, which process the sugars contained in the product.
- Candied. The method also has an industrial name - candling (derived from the English word candy - sweet / candy). A large amount of sugar added to the product removes moisture from it and kills bacteria. A striking example of candling are candied fruits.
- Smoking. Bacteria are destroyed in the product during the treatment with fire smoke. A huge plus of the method is the delicious aroma of the finished product.
- Sterilization. Products are exposed to strong heat, as a result of which bacteria die. If you heat the food several times in a row, you can destroy the spores - they are a more stable form of existence of microbes.
- Sealing. The method follows immediately after heating. Such a tandem eliminates the reproduction of bacteria that need oxygen for life.
It should be said that today canned products can also be considered those that are hermetically packed. Of course, before they get a reliable “clothing”, they can be processed by various methods, which will certainly affect the appearance of the product and its taste.
It is up to each person what to choose in the process of compiling a diet, but remember that canned food, even expensive and high quality, cannot be considered a natural product, so use them infrequently and for a short time.
Preservation methods
When canning at home, the following canning methods are most easily implemented and are most commonly used.
1. Sterilization. With this method of preservation, microorganisms die, and enzymes are destroyed as a result of heating food products placed in hermetically sealed jars. Sterilization is usually carried out at a temperature of 100–120 °C. Raw materials are filled with water or other filling.
2. Cooking fruits with sugar. When cooking sweet fruits, a product with a high concentration of sugar is obtained - 60–65% and more (jam, jam, marmalade, etc.).
3. Evaporation (concentration). In this way, fruit and vegetable juices or puree masses are processed. The juice (puree) is heated to remove much of the water it contains. Concentrated products are also an unfavorable environment for the development of microorganisms. Jam, vegetable puree and other products are prepared in this way.
4. Salting and pickling. This method of preserving fruits and vegetables is based on creating conditions under which fermentation proceeds with the formation of lactic acid.
5. Drying. This method removes most of the water it contains from the product. Dried foods are an unsuitable environment for the development of microorganisms due to their low moisture content.
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