Food preservation
Food preservation (from Latin conservare, “to get, to preserve”) describes the process of treating food so that it can be kept longer. The products treated and packaged in this way are called preserves (via preserve from Middle Latin conserva : in technical terms, 'medicinal product preserved with honey or sugar').
Preservation encompasses processes that are intended to stop or slow down the spoilage or deterioration of the food and its ingredients into inedible or harmful decomposition products . In addition, preservation can aim to stabilize and maintain nutritional value , taste , color and texture ( structure ) in the long term. Most procedures, however, require a compromise between these objectives. In many cases, the transition between the method of preparation and preservation of a food is fluid. Often it is precisely the method of preservation that defines a certain food as such.
The decay, which the preservation is supposed to prevent, usually occurs through biochemical processes such as microbial or enzymatic activity ( autolysis ). The most common application is the preservation of food in the context of industrial production, storage in the household , kitchen , in the context of self-sufficiency with food and as a preserving technique for food and similar natural objects in museums and collections . The emergence of a food industry and the production of ready-to-eat food on a large scale was only possible thanks to modern preservation processes.
history
Food preservation by salt , smoke , sugar or simple drying is the human race has long been known.
The beginning of modern heat preservation is mostly associated with the work of two French people : Around 1700 Denis Papin undertook experiments with preserving jellies and cooked meat in copper pots sealed with putty ; In 1809 Nicolas Appert presented technically mature methods of conservation. But the theoretical solution was accompanied by many technical problems, especially with soldering the cans and the duration of the heat exposure on different foods.
In 1864 \ 65 the French chemist and microbiologist Louis Pasteur invented the pasteurization process . This procedure represented a breakthrough in the understanding of the spoilage of food and its preservation. With experiments Pasteur refuted the thesis of the spontaneous development of spoilage pathogens (the internal development from the food itself). He proved that most of the spoilage pathogens are of microbiological origin and that infection with them comes from external sources. At the same time he found that microbiological harmful organisms and germs are omnipresent in the environment, both in environments with and without atmospheric oxygen. The pasteurization process (disinfection by briefly heating to temperatures just below 100 ° C) was registered for a patent and was initially conceived to stabilize wine. However, the process quickly found application in many areas of food preservation and beyond. Even if wines are nowadays often no longer pasteurized and we now know that there are also “food-internal” spoilage agents or causes, Pasteur's discoveries and developments must be viewed as milestones in the field of food preservation.
The first handicraft businesses emerged in the German Confederation in the 1840s. However, significant production volumes were not reached until the 1860s. Braunschweig was the pioneering region , the preferred product was the luxury good asparagus at the time .
In Switzerland, malt extract was introduced on the market from 1865 by Wander , condensed milk from 1866 from Anglo-Swiss Condensed Milk Co. , flour for infant nutrition from 1867 from Nestlé, and legume flours and powder soups from 1884 from Julius Maggi as industrially preserved products. In 1886, Henckell, Zeiler & Cie. a canning factory for fruits and vegetables.
The transition to industrial forms did not take place until the 1870s. The autoclave was introduced in Germany in 1873, and automatic can sealing machines as well since 1889 . The real breakthrough for canned food, however, came with department stores that had been selling canned food to a mass audience since 1892.
Despite high growth rates, canned food did not catch on as strongly in Germany as it did in Great Britain or the USA , for example . One reason for this was the relatively high prices that made consumption in the German Empire affordable only for the middle and upper classes . But an even more important reason was that canned food was perceived as a health risk. In the early days, lead poisoning occurred through soldering the cans with lead (soldering was later replaced by crimping as a closure method). Not only cases of poisoning , but above all the canning industry, which wrongly insisted on its expertise and the supposed non-toxicity of many preservation techniques and agents, led to a critical attitude. At the same time, the preservation of fruit , vegetables and meat by means of boiling became increasingly popular in households .
A fundamental change did not take place until the late 1930s with the implementation of cold preservation. The deep freezing was provided during the Nazi Four Year Plan supported by the state with high resources, then sat down but it was only in the early 1960s -Jahren generally by.
Typing
A distinction is made in the preservation of foodstuffs or luxury foods :
- Fully canned food with a very long shelf life of at least two years, at temperatures below 25 ° C for at least 4 years,
- Three-quarter canned foods that can be kept for up to 12 months (at max. 15 ° C),
- Semi- preserved foods ( preserves ) that can be kept below 5 ° C for at least 6 months,
- Tropical preserves, stable for at least one year at temperatures above 40 ° C,
- Long-term supplements not intended for human consumption.
Principles
In order to prevent biological decay, there are basic principles that also occur in combination:
- Harmful organisms are killed or their reproduction is inhibited.
- Contact with the harmful organism is eliminated and renewed contact is prevented.
- The harmful organism is deprived of one of the bases it needs.
- One of the ingredients is (for example by distillation or refining etc.) so highly concentrated or added in such a high concentration that it prevents the development of harmful organisms.
- Food additives such as preservatives inhibit the development of harmful organisms (see also list of food additives approved in the European Union # preservatives ).
- Food's own substances such as enzymes . Proteins are changed ( denatured ) in order to stop or slow down the chemical deterioration of the product.
- The food is protected from physical environmental influences or processed in such a way that it can retain its original properties for longer.
Notes on food spoilage
The deterioration of food, which should be slowed down or stopped by the preservation, describes the loss of certain desirable properties of a food, through which it may define itself as such.
Physical environmental influences, the food's own ingredients and microorganisms change a food through chemical processes. The food goes through an aging process, which is associated with the loss of freshness, progressive aging, overaging up to decay or rotting .
The further the spoilage has progressed, the more likely it is to have adverse health effects in the event of consumption. When a food is considered spoiled is, to a relative degree, a matter of taste. The health risks associated with the consumption of more or less spoiled food must also be assessed relatively. This applies in particular to particularly endangered risk groups, such as people with a weakened immune system (small children / pregnant women / sick people), who must be taken into account in a risk assessment.
While the food processing industry knows certain standards, such as maximum limits with regard to the microbial load, which can be checked in laboratories, in private use the consumer usually only has the orientation on best before dates or the assessment of the condition of the food based on their own senses. Basically, foods with a high protein content should be viewed particularly critically in this regard.
Examples of undesirable influences
Undesired physical influences
Physical influences can influence a food in an undesirable way and thus represent a form of spoilage or promote spoilage through other spoilage pathogens.
It can be:
- Unwanted drying out of the food due to external influences such as temperature and air
- An unwanted moisture absorption from the environment z. B. the surrounding air
- The influence of light can also affect a food and its ingredients e.g. B. dyes but also vitamins change and destroy undesirably.
- A taking place during storage contamination with non-biological pollutants such. B. Chemicals or dust is usually undesirable and can make food inedible, harmful to health or introduce other harmful organisms. In contrast to a load with z. B. chemical pesticides or poisons, the food can be protected from subsequent contamination by suitable measures such as packaging and storage.
Chemical and biochemical processes
Furthermore, the food's own ingredients and chemical reactions play a role in the spoilage of food. B. caused by enzymes , proteins .
Enzymes are food ingredients (mostly proteins), which in turn can break down or convert other proteins or ingredients. Certain ingredients also break down due to other influences such as B. Oxidation by oxygen over time into decomposition products ( metabolites ), which can be harmful to the consumer. Through changes ( denaturation , degradation), such ingredients (but also prions ) are stopped in their activity, strongly inhibited or stabilized. Many methods of preservation aimed at sterilizing food simultaneously cause certain ingredients to be denatured. This is the case, for example, with heating, but does not necessarily have to be accompanied by sterilization.
However, enzymes in particular can also be used specifically for processing (for breaking down or converting certain ingredients) of foods. Here, enzymes take over the change of other proteins, which leads to denaturation of the same by z. B. is similar to cooking and has the consequence that certain substances do not convert themselves into potentially harmful decomposition substances (metabolites) over time and remain stable.
Biological harmful organisms
- Animals: vertebrates such as mice, birds (especially as carriers of other infections ), insects such as worms, flies and their eggs and larvae
- Mushrooms: yeast mushrooms
- Bacteria : Salmonella , Clostridium botulinum , acetic acid bacteria , many others and their spores
Bacteria and fungi decompose food in a similar way to the food's own enzymes, but they also actively produce metabolic products that can be highly toxic to humans. These biological harmful organisms can be further divided into:
- aerobic (those that can live in an environment with atmospheric oxygen)
- anaerobic (those that can live in the absence of atmospheric oxygen)
Both groups contain organisms that produce very strong poisons (e.g. aerobic / mold , anaerobic / Clostridium botulinum ). In practice, this means that packed or liquid food can be colonized by dangerous germs even if the air is excluded.
Some organisms are not only able to decompose food and have a damaging effect in this way, but can also colonize the human body directly and only there produce metabolic products that are harmful to health.
Must be distinguished are viruses , certain bacteria such. B. Coli bacteria which are to be regarded as pathogens or parasites . These can persist in food for a while, but the food serves less as a breeding ground and more as a carrier. Such germs can also be destroyed through appropriate food hygiene or sterilization in the course of preservation.
While an infection of food by yeasts can be rated as harmless, both salmonella and certain molds, but especially bacteria such as Clostridium botulinum , should not be underestimated in their dangerousness. In particular, certain molds and the bacterium Clostridium botulinum (and relatives) produce highly dangerous toxins as metabolic products . Some of these very dangerous poisons are not very stable and theoretically it is also possible to sterilize a food that is already heavily infected , since the determination of the organisms (at least the bacteria) is hardly possible for the layman, however, should Under no circumstances try to make heavily infected foods edible again by boiling or frying them. Infested food should be disposed of immediately.
Typical characteristics of a spoiled canned food are:
- abnormal appearance such as visible mold, rot or an abnormal, usually pungent odor,
- the lifting or bulging of the lid on canned jars,
- the puffing / bulging of cans .
Progressive growth
A progression or resumption of growth e.g. B. the formation of sprouts or roots of vegetables should usually be prevented in the context of conservation.
Methods and procedures for preserving food
Preservation methods can be further broken down into
- physical methods,
- chemical methods without the aid of additives , preservatives or food additives to be declared with an E number ,
- chemical methods with the help of additives to be declared, preservatives or food additives with E number,
- chemical methods with the help of microbiological processes,
- microbiological methods,
- combined methods.
Physical methods and processes of preservation
Superficial cleaning
The cleaning of coarse soiling usually makes a food edible in the first place and thus a food.
A superficial cleaning also reduces the germ load and facilitates subsequent sterilization. While mechanical cleaning precedes most treatment methods, water cleaning is considered in some cases. Too high a moisture content, especially in the surface area, has a very negative effect on the shelf life of fresh foods. Cleaning with water must therefore usually be followed by a drying process. In this case, it must be considered whether cleaning after storage (before sale / consumption) might be more useful. Eggs are usually not cleaned with water either, since contact with water can promote and spread certain germs such as salmonella in the growth.
A cleaning with the help of additives such as acids or the removal of z. B. bowls can also bring about an additional germ reduction. In most cases, a food is not only colonized by germs on the surface, but also permeated by them. The following method of preservation must do justice to this fact or the given properties of the food.
A related topic is that of food hygiene .
Thermal processes
In these processes, spoilage pathogens are destroyed (heating) or their activity is inhibited (cooling).
With the thermal methods, it should be noted that the necessary or recommended temperatures always relate above all to the achievement and maintenance of a core temperature.
For adequate sterilization and denaturation, it is necessary to penetrate the food “through and through” that is, right into the inner “core” at a given temperature. In addition, this temperature must be maintained for a further period of time.
When cooking food at low temperatures, for example, core temperatures of 50 ° C to 90 ° C are aimed for and maintained. Although these temperatures are sufficiently high for the denaturation of certain proteins in the food, the process is much slower compared to cooking at higher temperatures.
This is also the case with regard to the destruction of microbial spoilage pathogens at temperatures above 60 ° C.
The temperatures and periods of time that must be maintained during heating in order to achieve the desired sterilization and denaturation depends on the nature of the food. On the one hand, the bacterial load, but also the protein and, above all, the water content of the products play a decisive role, since water is a very good conductor of heat.
The relationships can be illustrated using the example of a hard-boiled chicken egg. A chicken egg needs an average of 10 minutes in its shell at a water temperature of 100 ° C to completely coagulate. But if you whisk the egg into scrambled eggs and distribute it in a larger amount of 100 ° C hot water or a 200 ° C hot pan, the time for the proteins to coagulate can be greatly reduced. The example relates to the denaturation of proteins, but the situation is similar when it comes to the effects of heat on the harmful organisms it contains.
In the case of cooling food, a certain core temperature is also initially aimed for. As soon as the core temperature is reached, however, it must be ensured in the course of the cold chain that a food as a whole (in all its points) is kept at the same temperature ( Section 1 of the Regulation on frozen foods).
cooling
Food can be cooled at different temperatures in order to stop or slow down the activity of harmful organisms and other chemical processes. However, harmful organisms and enzymes cannot be sufficiently destroyed even at very low temperatures. If the cold chain is interrupted , these spoilage pathogens resume their activity (sometimes increasingly). With all methods of refrigeration, it must be noted that any interruption in the cold chain has a major impact on the further shelf life of the food.
This includes:
- The storage / renting of mostly fresh fruit and vegetables but also cheese or sausage at temperatures of around +15 ° C to + 1 ° C. This method slows down the decay and activity of harmful organisms over short to medium-term periods, depending on the food. Further ripening may be desirable during storage and this can be checked. On an industrial scale, for example, apples are stored at low temperatures and possibly an additional protective gas atmosphere and then ripened slowly. Another example is the storage of root vegetables in soil heaps . Another factor that must be taken into account with this type of storage is the humidity , which may have to be regulated. Prior cleaning with water should be considered, as too high a moisture content, especially on the surface of certain foods, has a very negative effect on the shelf life. Potatoes, root vegetables or mushrooms, for example, should not be cleaned with water before being stored fresh, or a drying process must follow.
- Storing fresh or processed food in standard refrigerators at temperatures from +5 ° C to +3 ° C slows down the activity of harmful organisms and enzymes over short / medium-term periods. At the same time, this storage method protects against other environmental influences such as B. Light
- Freezing in typical household freezers at temperatures of around −18 ° C to −25 ° C : This stops or slows down the activity of enzymes and harmful organisms over long periods of time. However, this type of freezing usually has negative effects on z. B. the consistency of the food. Due to the low cooling capacity and correspondingly long freezing times, large ice crystals arise when freezing, which negatively affect the structure of the food.
- The freezing / blast freezing in the industrial area at temperatures down to -50 ° C : This procedure stops the activity of enzymes and harmful organisms for extended periods of time and is easy on the consistency and ingredients of food. The rapid freezing at very low temperatures creates smaller ice crystals than household appliances, which means that the structure of the food is better preserved. At temperatures around −50 ° C, high-performance machines bring food to core temperatures of -18 \ -25 ° C very quickly. With powerful machines and circulating air, even warm preparations can be cooled down quickly. After deep-freezing, the food is stored at temperatures between −18 ° C − 25 ° C. According to the law, fluctuations in the specified maximum temperatures for frozen goods of −18 ° C by a maximum of 3 ° C are tolerated. Examples: Frozen food from the trade ( Section 2 of the Regulation on Frozen Food).
Heat
By heating depending on the temperature and length of time living harmful organisms or even destroy their spores. In addition, ingredients such as proteins, enzymes (but also prions or poisons) are denatured, which regulates their decay / activity.
The temperatures and periods of time that must be maintained in order to achieve the desired sterilization and denaturation depend on the nature of the food. On the one hand, the bacterial load, but also the protein and water content of the products play a decisive role.
In the case of many products, it must also be assumed that the canned food will not be reheated before consumption. Accordingly, the food, not only in the case of z. B. Sausage spread, but also all kinds of preparations, sufficiently cooked, denatured and sterilized to ensure food safety.
In addition, it must be taken into account that food that has been processed / sterilized by heat must also be treated by chemical processes, cooled or at the same time (subsequently) sealed airtight. After heating, even the smallest contact with unfiltered air or unsterile objects can lead to renewed contamination with harmful pathogens.
- Pasteurization : The brief heating of food to temperatures of 60 ° C to a maximum of 100 ° C. Pasteurization at relatively low temperatures and short periods of time is gentle on certain ingredients of the food, such as B. Vitamins. Since the food is not cooked in this way, properties such as consistency (e.g. “crunchiness”) can be retained in suitable products. In contrast to boiling or autoclaving, sterilization (and denaturation) through pasteurization is only sufficient for certain foods. These include B. low protein, but high water content foods with higher acid concentrations. Bacterial and mold spores are not destroyed in the process. One area of application is e.g. B. the prevention or interruption of a fermentation process by killing the yeasts or lactic acid bacteria. Most pasteurized foods are preserved through additional combined processes. Examples: fruit juices, traditional milk, pickled preserves,
- Cooking , boiling , boiling , by boiling : the water reaches a temperature of 100 ° C at a "normal" atmospheric pressure. Boiling destroys most of the living harmful organisms. In order to ensure adequate disinfection and denaturation of the proteins, a certain period of time for the boiling process must be taken into account, depending on the contamination, protein and water content of the food. The spore stages of bacteria and fungi are only partially killed by boiling at 100 ° C. A clear distinction must be made between boiling (boiling) and boiling through (heating through). When cooked through, all components of the food should have reached the cooking temperature - see also core temperature. Food treated in this way is, as everyday life shows, safely preserved for one day. A safe longer preservation requires further follow-up treatment.
- Bottling / canning : A typical application for long-term preservation of food by boiling the boil in Einkochgläsern. With this method you have to adhere to certain cooking times, depending on the food, in order to achieve sufficient sterility (and denaturation). The recommendations for canning times try to keep the cooking times and temperatures as low as possible, depending on the food, in order to enable gentle cooking. However, if you attach great importance to sterility and shelf life for foods with an uncertainly high bacterial load or a corresponding consistency, you have to consider that the maximum temperature when boiling is limited to 100 ° C. Since the spores of various fungi and bacteria are not destroyed at these temperatures, heavily contaminated foods may have to be boiled twice. Some sources assume that repeated boiling down of certain foods aims to germinate possibly persistent spore stages of spoilage pathogens during the first boiling process and to kill them in the second "boiling process". However, since microorganisms are usually present in such high numbers that active organisms and their spore stages exist at all times, this explanation is questionable. Other sources assume that with certain foods such as legumes, the first "boiling process" helps to accelerate the water absorption, the swelling of the food, so that sufficient water is absorbed in the meantime and that in the subsequent cooking process through sufficient water as a heat conductor Core of the food, the core temperature required for sterilization and denaturation can be achieved. High protein products with a low water content - such as meat or legumes and preparations made from them - are sterilized on an industrial scale at higher temperatures for safety reasons. The food is hermetically sealedduring the process of preserving and preserving. There is also the option of cooking food packed in special heat-resistant foils instead of jars (see also vacuum cooking). In this way, too, the food is protected from renewed contamination from the environment after the cooking process. Examples: Glass preserves from the canning pot .
- Baking / roasting / deep-frying : These processing methods reach higher temperatures (at least on the surface) than when cooking. When deep-frying, core temperatures similar to those achieved when "boiling through" can be achieved. Often, however, food is only “pre-fried” very briefly and on the surface and only cooked and brought to the desired core temperature in the course of later preparations. The food treated in this way must be further processed for longer-term preservation, such as B. be frozen or packaged in a protective gas atmosphere.
- Sterilization in an autoclave at 110–130 ° C (wet canning): With sterilization / autoclaving, food is made almost completely sterile. Certain food ingredients such as heat-sensitive vitamins are not spared in this process, and the consistency is also changed by the cooking process. The physical-technical process of autoclaving is based on the fact that watercan reach temperatures higher than 100 ° Cunder increased pressure . When the pressure is increased by 1 bar (relative pressure based on sea level), water reaches a temperature of slightly less than 110 ° C. With an increase of 2 bar, the water already reaches a temperature of around 120 ° C. This increase in temperature and the prevailing overpressure kill harmful organisms faster and more reliably than simply boiling them at 100 ° C at normal atmospheric pressure . In addition, this process not only kills living bacteria and fungal strains, but also their spore stages. These pressures and temperatures are achieved using special pressure vessels. Thepressure cookers / pressure cookers commonly used in the homework on the same principle and can be used in a similar way to preserve food. These common household pots usually only reach pressures of max. +2 bar and temperatures of max. 120 ° C (usually even less). In principle, autoclaves are nothing more than large pressure pots, which in the food sector, however, reach pressures of +3 bar and temperatures of around 130 ° C and more. This is done either in a water bath or the air inside the container is replaced by water vapor . In addition, a number of other methods derived from this principle, such as sprinkling autoclaves, etc., are used in industrial applications. The pressures and temperatures achieved in this way then guarantee an almost complete sterilization of particularly critical foods such as meat products, legumes or preparations with a high protein content and a correspondingly high probability of shelf life. To make sure that the food heated in the autoclave has reached a certain core temperature, many devices have a temperature sensor. This sensor is placed in a measuring dummy (e.g. a tin can) in such a way that the core temperature of the food it contains can be monitored by way of example. Even if simple systems, which are used in a similar form for the sterilization of instruments in the field of surgery , beekeeping , mushroom cultivation, etc., are now also available for private users, there are some practical problems with the preservation of food in the privatesector, as there are complications regarding of pressure equalization, pressure build-up and pressure drop within the system. These problems are due to the fact that inexpensive devices do not have automatic control of the process. If the protection of sensitive ingredients is negligible, the autoclaving of canned food is one of the safest methods of preservation by exposure to temperature. Examples: many commercially available canned and glass preserves, especially meat products and preparations with a high protein content such as soups, stews, goulash, canned sausage / meat and fish.
- Ultra-high-temperature heating (Uperization, UHT): Temperatures of 135 ° C are briefly reached and the food is then cooled down again very quickly . Examples: UHT milk
Drying
During the drying process, moisture (water) is removed from the food. This procedure deprives the harmful organisms and enzymes of their basic activity. In combination with appropriate storage, food can be preserved for a very long time.
It should be noted that many organisms are adjusted to such changes in their environment and survive in their spore stages. Similar to freezing, they can also resume their activity during drying in the event of rewetting. For this reason, too, certain properties of the dried food must be taken into account so that it does not absorb moisture again after drying or during storage.
Due to the concentration of ingredients and the strong change in consistency, drying always affects the taste of the food. Re-moistening partially offsets these effects.
- Air drying : Air drying removes moisture from the food in a natural way. After z. B. fruits their natural water supply has been interrupted, these are dried in dry, possibly additionally moving air. Depending on the weather, this can be done directly outdoors, e.g. B. common with cereals and legumes, or also take place in ventilated rooms (e.g. after-drying of onions). In areas with a suitable climate, foods with a high water content such as tomatoes or peppers can easily be air-dried. But even in cold areas with sufficiently dry moving air, food can be dried without additional aids, e.g. B. Stockfish in Scandinavian countries. Cheese and sausage are also partially air-dried.
- Dehydration : During dehydration, moisture (water) is removed from the food through heat or greatly reduced humidity. However, drying can have a strong impact on the taste, consistency and texture of the food. Examples are dried fruit, dried mushrooms or pasta.
- Freeze-drying ( sublimation drying ) : The freeze-drying of food mostly goes hand in hand with prior deep freezing / shock freezing. The process is based on the fact that water can be converted from the frozen state directly into the gaseous state in a vacuum without becoming liquid. Freeze drying preserves the consistency and structure of food relatively well compared to other drying methods, and ingredients are also conserved. Both solid and liquid foods can be dried / pulverized with this method. The process is mostly used in the industrial sector; Recently, however, a market for devices for private use has also developed. Examples are: instant coffee , raspberries in muesli, trekking or astronaut food , bag soups
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special industrial processes of drying :
- Vacuum drying (evaporation): Since water boils and evaporates in a vacuum even at very low temperatures, heat-sensitive ingredients such as vitamins can be spared when water is reduced in a vacuum. Examples: fruit juice concentrates
- Spray drying in a stream of heat or vacuum: With spray drying, liquid mixtures are processed into dry powder. Example: milk powder
- Roller drying and others.
Filtration
By using fine filters, food can be made sterile. In wine and juice production, suspended matter, but also z. B. yeasts separated with the help of fine filters. Water can be filtered germ-free through suitable membranes ( reverse osmosis ). Milk is also sterilized by microfiltration , among other things .
Insertion
- Soaking in cooking oil : When soaking in cooking oil, food that is dry or with a reduced moisture content is usually inserted airtight. The oil protects the food from air and provides a relatively poor breeding ground for harmful organisms. The oil often absorbs the flavor of the pickled food and is used as such itself. It should be noted that untreated, fresh and moist foods in oil only have a very limited shelf life. To preserve them for a longer period of time, these foods have to be added, e.g. B. be treated by heat. However, heat treatment only makes sense with heat-stable cooking oils. For example, cold-pressed olive oils should not be additionally heated. It must also be borne in mind that, depending on the temperature and moisture content of the food, oil-water emulsions or water deposits in the glass can occur. A similar method is the confection of meat in its own fat (see confection).
- Soaking in high-percentage alcohol ( ethanol ) : Food can be soaked in high-percentage alcohol. Ethanol has a disinfectant and thus preservative effect in a sufficiently high dose (from around 50% by volume). The disinfecting effect is based on the fact that, similar to a cooking process or the action of acids , ethanol is able to denature proteins and kill microbes. Alcohol always has a strong effect on the taste of the pickled foods.
- Konfieren / Confieren referred various combined methods of preparation and preservation of food. The methods have their origins in traditional French cuisine and still have their place in cooking, gastronomy and cuisine today. Beyond that, however, they are no longer of any importance as methods of preservation in the food industry. Confectioning includes methods of sweet, sour or salty pickling, e.g. B. in sugar solution ( candying ). Most often, however, the term is used in connection with a special preparation method for meat ( confit ). In this context, confection refers to the slow cooking of mostly high-fat meat (e.g. poultry) in the animal's own fat. To preserve it, the cooked meat is later layered in containers and covered with the animal fat. By storing it in fat, the meat is protected from air and harmful organisms and thus preserved. To preserve them, foods cooked in fat, their own juice, stocks or broths can be covered with clarified animal fats or oils and stored in suitable containers such as preserving jars. Depending on the food used and the hygiene during the confectioning process, food treated in this way can be kept for several weeks to months, either refrigerated or not.
packaging
The methods of packaging , which are mostly only used in combination with other processes , which represent protection against environmental influences and renewed contact with harmful pathogens, are also considered to be physical methods.
The outer packaging may, depending on purpose and application of bags, sheets, jars, cans, cardboard boxes but also coatings such as, for example, consist of wax and is complemented by other processes:
- Vacuum sealing : Wet and dry preserves are packed in jars, foils and other containers before, after or during the preservation process with the exclusion of air.
- Packaging in a protective gas atmosphere : Processed or fresh food is stored in halls, containers or even tightly sealable packaging with exclusion of air in a protective gas atmosphere. Examples of such protective gases are concentrated nitrogen or carbon dioxide (see also Modified Atmosphere Packaging ).
- Packaging / storage with exclusion of light : Light is also able to break down certain ingredients of food. This applies to dyes , among other things . For this reason, many foods are kept in opaque containers such as tinted bottles or dark storage rooms.
distillation
During the distillation , certain ingredients of a food are so highly concentrated that an environment hostile to harmful organisms is created. During the distillation of ethanol from fermented mash , spoilage pathogens such as vinegar bacteria are killed by heat and at the same time the ethanol content is so highly concentrated that most harmful organisms are deprived of their breeding ground. From around 50% by volume, ethanol has a disinfectant effect against most microbes.
Further methods of preservation from the industrial sector
Furthermore, there are various special industrially used methods that can be counted among the physical processes:
- Plasma sterilization
- High pressure sterilization
- Ultraviolet radiation sterilization
- Sterilization by ionizing radiation
Chemical methods / processes for preservation
The chemical methods for preserving food can be divided into methods with or without the aid of declarable preservatives (food additives with E number)
The transition from chemical methods of preservation without any preservatives to be labeled and chemical methods with the help of additives to be declared is fluid. Since many additives and preservatives are at least formerly of natural origin, z. B. Certain acids can be viewed as both declared preservatives or as a naturally given component of a preparation.
Chemical methods / processes for preservation without the aid of food additives
Salting Salting
- Salts / salting / curing / pickling : The preservative salt is based inter alia on the principle of suppressing the growth of spoilage by osmosis . Salt is highly hygroscopic and removes moisture from foods that contain water. If this is not removed, a “brew” of salt solution is created. Since saline solution has a high osmotic potential, it removes the cellular fluid from harmful organisms, which are usually small in number . In the case of heavily salted foods, salting always goes hand in hand with dehydration and, with the appropriate dosage, can be preserved for a long time without additional treatment (e.g. herbal salts, salted vegetables, fish, pickled fish / meat). It should be noted that food dried by salt tends to absorb moisture from the air again, which can be prevented by suitable packaging. Salting always has a more or less effect on the taste of the food. A special case is curing with nitrite curing salt , which is used for the production of meat and sausage products to prevent discoloration of the meat and infection with the bacterium Clostridium botulinum (nitrite curing salt is, however, an additive to be identified).
- Soaking in salt solution / brine : When food is soaked in brine (salt solution in different concentrations), the growth and germination of harmful organisms is made more difficult. Depending on the concentration, foods prepared in this way must also, for. B. be treated with heat, since less saturated salt concentrations alone are not able to permanently prevent the growth of spoilage pathogens. The spore stages of harmful organisms are also not killed in saline solution. In addition, the addition of salt (like sugar) in certain doses has a taste-preserving effect. If there is too much salt or sugar imbalance between the food and the brew, osmosis can water down the food or release the ingredients into the brew. The brew can be balanced isotonically with sugar and salt , so that a food does not lose too much of its taste or structure in this way.
Sugar
Preservation using sugar is based on a similar principle to salting. Sugar solution is also able to remove the cell fluid from the cells of harmful organisms by osmosis and thus kill them.
- Soaking in sugar solutions : Sugar solutions come when placing food - e.g. B. Fruit - used in a more or less concentrated form, whereby further treatments are required for longer-term preservation (e.g. heating, acidification). An example is jam or marmalade , which is a form of high doses of sugar solution. In connection with acidification and heating, this can have a very long shelf life with but also without exclusion of air. In the appropriate dosage, sugar can also have a taste-preserving effect. If there is too much salt or sugar imbalance between the food and the brew, osmosis can water down the food or release the ingredients into the brew. The brew can be balanced isotonically with sugar and salt , so that a food does not lose too much of its taste or structure in this way. Examples are many commercially available canned foods, jams, and honey.
- Candying : When candying, the moisture in food (mostly fruit) is replaced by a sugar solution. So these can be made durable for a long time. Examples: candied fruit
pH value regulation
By regulating the pH value of food, acidic or basic environments can be created that inhibit the growth of harmful organisms.
The taste of the food is changed depending on the dosage of acids (PH-) or bases (PH +). In addition, this is also used specifically to change the taste (edible acids). Acids are also able to change proteins and enzymes in food , similar to a cooking process .
It should be noted that a change in pH does not necessarily have to stand out in terms of taste. For some food preparations, such as pickled foods (e.g. pickled cucumbers), a clear acidic taste is desirable, however, an inlay can have a very low pH value even if the acidic taste is not so important.
- Acidification : The acidification of food can e.g. B. by already contained acids like with many types of fruit or by adding acidulants. Typical pickles are pickled cucumbers or onions, but other acidulants from the field of additives can also be used to regulate the pH value, e.g. B. acetic acid, malic acid, tartaric acid, citric acid, hydrochloric acid or lactic acid. Pure lactic acid is a food additive , but it can also be added to food through lactic acid fermentation . In the latter case, the resulting lactic acid should not be regarded as an additive. Examples are: pickled cucumbers, but also most canned vegetables or fruit are acidified (pH-regulated) to improve shelf life. At the same time, the acidification has the effect of enhancing the taste, even if it is barely noticeable.
- Lyes / bases : In principle, a strongly alkaline environment can also inhibit the growth of certain harmful organisms. Substances from the field of food additives that have an alkaline effect in aqueous solution include various carbonates . Usually these substances are only used to regulate the pH value to a small extent for reasons of taste or to improve other properties related to it (such as gelling ability). A strong increase in the pH value, as would be necessary for preservation, would, however, remove all acids as important taste components in the food. In addition, the inherent taste caused by the high concentration of hydroxide ions, in contrast to acidification, is usually perceived as inedible. For these reasons, a strong increase in the pH value for the purpose of conservation is rarely used in practice.
Refining
By refining a food is purified of unwanted substances and thus prepared concentrated. For example, oils can be freed of accompanying substances, which harmful organisms are no longer available as a breeding ground. The rancidity of oils and fats is also contained in this way.
Smoking
Smoking can be viewed as a combination of physical and chemical preservation. With this type of preservation, the food is either cooked by heat or dried, depending on the method, but chemical ingredients in the smoke also have a preservative effect.
- When cold smoking , temperatures of 15-25 ° C are reached.
- With hot smoking , on the other hand, temperatures of around 80 ° C are reached, which results in a greater reduction in the water content and a cooking process. As a result, hot-smoked foods have a potentially longer shelf life. Examples are smoked fish, meat or cheese.
Chemical methods of preservation with the help of food additives
(see the list of food additives approved in the European Union # preservatives)
Special preservatives : are used to maintain very specific properties such as: B .:
- Water storage capacity of baked goods, for example, through swelling agents or humectants such as glycerine
- Color retention through antioxidants such as ascorbic acid
- Structure retention such as flowability through release agents or stabilizers
- antibiotic substances
The preservatives used can be of natural origin or nature-identical. In the field of food additives, however, fully synthetic substances are also used.
Widely used preservatives to be declared are z. B. various acids such as sorbic acid , sulfur in wine and dried fruit (see also sulfurization ) or antioxidants such as ascorbic acid.
Fumigation: Fumigation with gases such as pure nitrogen can kill both macrobiological pests and microbes. The gas is used as an auxiliary material which is then no longer contained in the food.
Chemical methods of preservation with the aid of microbiological processes
The modification of protein-rich or carbohydrate-rich raw materials with the help of microorganisms leads to new products that usually have a better shelf life than the original. It is not just a question of preservation, but also of refinement (a “desired spoilage”) - see also dairy products .
Here too , enzymes produced by microbes often play a role. B. Bacteria are able to metabolize the ingredients of the food to convert them and actively produce substances such as lactic acid.
A related topic is that of auxiliary materials that are used in food processing but are later no longer contained in the food and do not have to be declared. This topic is often controversial because certain enzymes are produced by genetically modified organisms.
Fermentation and fermentation
- Alcoholic fermentation : In alcoholic fermentation, sugar is fermented into alcohol, which in sufficient doses represents a hostile environment for many (but not all) microorganisms or even has a disinfecting / killing effect. Vinegar bacteria z. B. can use alcohol as a livelihood under certain conditions; For this reason, alcohol must also have an antibacterial effect, e.g. B. be concentrated by distillation. Beverages with only moderate ethanol content, such as wine or beer, require additional processes such as heating, filtering or the addition of sulfur; Due to its high acid content,sour must / cider can have a long shelf life even without additional processes. Brandies and schnapps achieve a significantly higher alcohol content through the distillation process and can be kept for a very long time in the absence of air. Ethanol concentrations of 50% by volume or more can then also be used to insert other foods. Examples: wine , brandy , schnapps , cider / must
- Vinegar fermentation : In vinegar fermentation, alcohol is fermented into vinegar with the help of vinegar bacteria at certain temperatures and with a supply of oxygen. This creates a strongly acidic environment that is hostile to most harmful organisms. Examples: vinegar
- Lactic acid fermentation : In lactic acid fermentation, lactic acid bacteria process sugars such as lactose or starch in food into lactic acid. This creates an acidic environment that is hostile to many harmful organisms. Lactic acid bacteria are anaerobic bacteria and, like yeast, are widespread in nature. Spores of the bacteria are therefore present in almost every food or can be added through starter cultures. With exclusion of air, e.g. B. in weakly concentrated salt water, the bacteria multiply and begin fermentation. Many sugary or starchy foods such as vegetables or dairy products are suitable. The production of yogurt and sour milk cheese also involves lactic acid fermentation, which is achieved by lactobacteria and the exclusion of air. Examples: sauerkraut , yoghurt, cheese, wet silage (cattle feed)
- Fermentation by enzymes ( rennet ): By adding enzymes (rennet) to milk, solid fats and proteins are separated from the water in the milk, which enables the moisture content to be greatly reduced. This is further reduced by air drying and treatment with salt. Examples: cheese , dairy products . The preservation of pickled herring ( matjes ) is also based on treatment with the fish's own enzymes, which, similar to a cooking process, metabolize or denature the ingredients of the fish. On the one hand, this gives the fish its delicate structure; on the other hand, the process, in addition to soaking it in salt or vinegar, contributes to the shelf life of the fish.
Microbiological methods of preservation
In the purely microbiological methods of preservation, a food is colonized with harmless organisms, which, as food competitors, remove the nutrient medium. Examples: noble mold
Examples of common combined methods and processes of preservation
- When boiling / autoclaving wet canned food, in addition to being heated, the food is usually salted, sugared (or both), the pH value is regulated (usually acidified), vacuum-sealed and hermetically sealed.
- Pickled foods in vinegar or oil are additionally heated (in the sense of pasteurization / preserving), vacuum-sealed and hermetically sealed.
- Food chilled in the refrigerator is also packaged, chemically treated and stored in the dark.
- When freezing, foods are used to avoid z. B. Freezer burns additionally packed under the exclusion of air (vacuum, protective gas) or covered with a protective layer of water ice ( glazed ). Preparations can also be treated chemically.
- Smoking, a physical and chemical combination of heating, drying and wrapping with preserving substances, subsequent packaging with exclusion of air and possible cooling.
- When cooking jam, an increase in the sugar concentration is combined with souring, heating and the subsequent / simultaneous packaging under the exclusion of air / vacuum.
- In the case of dehydration, the reduction of the water content, a possible increase in the sugar concentration and the subsequent packaging with the exclusion of air, soaking in oil or salting, are combined.
- Confection refers to the cooking and then soaking of meat in fat or oil, combining heating and soaking in the absence of air.
Long-term preparations not intended for human consumption
For the long-term preservation of food in order to For example, to display in museums, other methods of preservation are used. In principle, common conservation methods for long-term biological preparations are suitable, such as B .:
- the freeze drying ;
- soaking in formaldehyde solution ( formalin ) or alcohol;
- the Plastination by plastics such as silicone , acrylic or epoxy resins .
A particular challenge here is the preservation of dyes, which can be achieved through special additives or natural coloring.
Choosing the appropriate method
For the selection of a suitable method for preserving a food, the desired taste or the desired end product is primarily decisive. In many cases, a food is primarily defined by the method of preservation used.
If different methods come into question, it must be decided which properties are to be retained in a particular way. A particularly long shelf life is z. B. must be weighed against the preservation of sensitive ingredients.
In addition, the (cost) effort must be taken into account as a factor. While many foods have to be processed quickly and in large quantities depending on the season, other foods are produced and preserved in smaller batches . In the mass production of z. B. Canned vegetables require processes that enable non-stop processing. In such cases, the sterilization / pasteurization takes place in a continuous process in a production line . Other methods cannot be implemented in a continuous process and are therefore unable to carry out such mass processing.
An example of particularly complex industrial processes is that of freeze drying . Relatively small systems have to be charged for freeze drying; In addition, when freeze drying, food must be frozen and then reheated. In addition, a vacuum must be maintained and moisture must be bound. For this reason, the process usually only processes higher quality foods from the outset. All of this naturally affects the price. So it happens that in one kilogram of inexpensive muesli you can definitely find 400 g of raisins, but you have to look for the freeze-dried raspberries with a magnifying glass even in high-priced muesli.
Ultimately, it is methods that are applied to the smallest extent by hand in the sense of manufacture , such as the production and maturation of cheese and sausage products on a small scale, which are probably to be regarded as the most complex preservation processes.
Trivia
There is a Norsk Hermetikkmuseet (canning museum) in Stavanger ( Norway ).
See also
- Food safety
- Food
- food industry
- Food additive
- List of food additives
- Spoilage
- Preservation
- disinfection
- sterilization
- Portal: food and drink
literature
- Christel Rademacher, Heike Rapp: Preserving food. Bonn 1994 (= aid brochure No. 1270)
- Uwe Spiekermann : Jumps in Time: Food Preservation Between Household and Industry 1880–1940. In: Food culture through the ages. Edited by KATALYSE eV and BUNTSTIFT eV, Cologne 1997, pp. 30–42.
- A. Hausner: The manufacture of canned goods and candies. In: Hartleben's chemical-technical library . Volume 23. 5th edition. A. Hartleben's Verlag, Vienna 1921
Web links
- Preserving food: preserving
- https://www.bzfe.de/
- https://www.bvl.bund.de/
- http://www.bfr.bund.de/
- https://www.lgl.bayern.de/lebensmittel
Individual evidence
- ^ Willem Frans Daems: Dosage forms. In: Lexikon des Mittelalters I (1980), Sp. 1094-1096, here: Sp. 1095 .; see. also Otto Zekert (ed.): Dispensatorium pro pharmacopoeis Viennensibus in Austria 1570. Berlin 1938, p. 140 ( herbal sugar ). See also Gotthilf Wilhelm Schwartze : Pharmakologische Tables on the “Spoonbill Conserve”, for example . [...]. Volume 1, Leipzig 1819, p. 194: Spoonbill Conserve (Conserva Cochleariae) .
- ^ History . In: Institut Pasteur . November 10, 2016 ( pasteur.fr [accessed October 2, 2017]).
- ^ Albert Pfiffner: canning industry. In: Historical Lexicon of Switzerland . October 28, 2008 , accessed February 23, 2020 .
- ^ Andreas Steigmeier: Hero. In: Historical Lexicon of Switzerland . August 30, 2006 , accessed February 23, 2020 .
- ↑ Gert Hartwig, Heiko von der Linden, Hans Peter Skrobisch: Thermal preservation in the food industry. Behr's Verlag, 2014, ISBN 978-3-95468-218-8 , p. 74. ( limited preview in Google book search)
- ↑ Dr. Gesine Schulze Bavarian State Office for Health and Food Safety: Food: Verderb - Internet offer. Retrieved September 28, 2017 .
- ↑ Recognize food spoilage: eat it or throw it away? Retrieved September 28, 2017 .
- ↑ BVL - Undesirable substances and organisms. Retrieved September 28, 2017 .
- ↑ Assessment of microbial risks in food - BfR. Retrieved September 28, 2017 .
- ↑ Amal Wicke: Microbial spoilage of plant-based foods. (PDF) In: Halle lecture afternoon. State Office for Consumer Protection Saxony-Anhalt, May 10, 2006, accessed on September 28, 2017 .
- ↑ Freezing: freezing food properly. Retrieved September 28, 2017 .
- ↑ Preserving: Preserving, canning or preserving. Retrieved September 28, 2017 .
- ↑ Drying: Preservation by removing water. Retrieved September 28, 2017 .
- ↑ Soaking: Well stored in vinegar, oil & alcohol. Retrieved September 28, 2017 .
- ^ Frank Massholder: Confit, Konfieren: Preservation: Definition, product knowledge, food science. Retrieved October 28, 2017 .
- ↑ Dr. Gesine Schulze Bavarian State Office for Health and Food Safety, Brigitte Butz Bavarian State Office for Health and Food Safety: Food: Food technology - Internet offer. Retrieved September 28, 2017 .
- ↑ Salting and curing: preserving meat and fish. Retrieved September 28, 2017 .
- ↑ Sugar: jam, marmalade and jelly. Retrieved September 28, 2017 .
- ↑ Additives: Technically necessary helpers in processed foods. Retrieved September 28, 2017 .
- ↑ Fermentation: ferment vegetables until lactic acid. Retrieved September 28, 2017 .