Food preservation methods

Food preservation methods

Food preservation methods

Food processing techniques to prevent food deterioration and ensure good condition during consumption

Human beings have always preserved food with the aim of keeping it edible for as long as possible. It is evident that the mechanisms used nowadays by the food industry are quiet different from those used in the past, although the knowledge of our ancestors has laid the foundations for everything we know today.

In this article we will introduce you to the wide variety of techniques for preserving foods of plant and animal origin.

Main causes of food spoilage

Below, we will classify the various agents that can cause food spoilage:

Moldy tomato, need to apply food preservation methods
  • Physical agents, those external elements that directly impact and alter the external appearance of the preserved food:
    • Temperature.
    • Humidity.
    • Air.
    • Light.
  • Chemical agents, which usually change internal aspects of food, for example, natural nutrients undergo chemical changes that can reduce their efficacy when consumed:
    • Oxidation of vitamins.
    • Protein decomposition, which produces a bad odor.
    • Fermentation of carbohydrates that produces a spicy flavor and sometimes forms gas.
    • Rancidity of lipids.
    • Browning of food, called a Maillard reaction, which is produced by the combination of the derivatives of sugars and certain proteins.
  • Biological agents, which can either be intrinsic components: such as enzymes, which are responsible for causing oxidation and browning in fruits and vegetables such as peeled apples or potatoes or extrinsic elements: such as biologic agents, such as insects, parasites or microorganisms (bacteria, fungi and virus among others).

Food preservation methods

There are many methods of food preservation used to slow down food deterioration, prevent food poisoning and extend food best before dates. In this article we will briefly explain the most popular methods:

Low-temperature food preservation methods

Frozen vegetables, low temperature food preservation methods


Preservation technique using refrigerators, which consists of lowering the temperature between 0-5ºC, so that the bacteria present in the food takes time to proliferate and the enzymes in the food work more slowly.


Similar to the above, but with a reduction in temperature to -18ºC, so that the water in the food turns to ice and the bacteria cannot proliferate as there is no liquid water. However, this does not mean that bacteria are eradicated, they are merely frozen and therefore cannot proliferate.

Deep freezing

Consists of subjecting the food to temperatures below -40ºC for a short period of time, a maximum of 2 hours, and then keeping the product in normal freezing temperatures.

· The cold delays the proliferation of microorganisms and allows the food to retain its nutritional properties for large periods of time.

· Both freezing and deep-freezing are the most effective methods of preservation and the techniques that change the organioleptic and nutritional properties of the product the least. Likewise, both allow the food to be preserved for long periods of time, up to several years in some circumstances.
· Low-temperature techniques do not inactivate posterior microorganism growth after thawing.

· The conservation of food at low temperatures allows food to be preserved for a limited time, days, weeks or months and, obviously, these products always require refrigeration during transport and storage.

High-temperature food preservation methods

TERRA Food-Tech autoclave for the sterilization and pasteurization of preserves, methods of food preservation using heat

Scalding or boiling

Not a preservation method per se. It is usually the step before freezing, especially for vegetables. Vegetables are submerged in boiling water for a few seconds to partially destroy microorganisms from the surface.


Sterilization is a procedure that consists of subjecting food to high temperatures for a certain period of time in order to completely inactivate all microorganisms, pathogenic or not, and their spores. We can sterilize all kinds of meat, fish, vegetables and fruits. This technique is used in jams, syrups, pickles, creams, soups, sauces and stews, among many other food forms..


Unlike sterilization, pasteurization uses lower temperatures, below 100ºC, and the process does not completely eliminate microorganisms and spores. Milk and its derivatives, flavored juices and beers are usually pasteurized, but also ready meals and some sauces.

· From a microbiological point of view, sterilization is the safest food preservation method. It manages to eliminate all bacteria and fungi, including spores.

· Sterilization provides the longest shelf life. More than 4 months and, depending on the type of food, this time can be extended to 2 or 5 years.

· Pasteurization is the process by which the aromas are not excessively volatilized and the flavor and nutritional properties remain unchanged.

· No chemical additives are required in sterilization, so gourmet preserves and/or natural ready meals can be obtained without additives or artificial preservatives.
· With sterilization, by applying such high temperatures, above 100ºC, the properties of the food can be altered and some of its nutrients and vitamins can be lost.

· Pasteurization does not totally kill all bacteria. Therefore, pasteurized products should be kept refrigerated at all times during transport and storage.

· Pasteurization best before dates are very limited, could be from days to a month.

Water content reduction as a food preservation method

Bowl with dehydrated apples, one of the methods of preserving food by heat by modifying the amount of water

As bacteria and other microorganisms require water for their development, by controlling the moisture of the food, their growth is hindered.

The most common techniques include:

Hot dehydration

The total or partial extraction of the water content of a food through the application of heat.

Natural drying

Traditional method based on removing moisture from food by exposing it to natural environmental conditions, especially the sun, so that it loses most of its water through evaporation. Products obtained by this method include mojama, dried cod or raisins, among others.

Freeze-drying (Cold drying)

Consists of subjecting the product to a very rapid freezing (below -30ºC) and then heating it under vacuum conditions and thus eliminating the water. What happens is that the water content goes from solid (ice) to gas (vapor) through sublimation, that is, without going through the liquid phase.


This procedure does not completely dry the product but substantially reduces water. There are several methods to achieve this such as membrane microfiltration or reverse osmosis.

· Dehydration prevents the development of microorganisms and also limits the activity of enzymes.· Freeze-drying is a very effective food preservation method that also keeps its properties in perfect condition. But, due to the number of steps to go through, it is usually more profitable on a large scale. Therefore, it tends to be used mainly at the industrial level.

Food preservation methods based on irradiation


Consists of exposing the product to ionizing or electromagnetic radiation (X-rays or UV-c) or high-energy particles for a specific period of time. It is a very common method in the food industry.

· Countless studies have been carried out by international organizations such as the Food and Agriculture Organization of the United Nations (FAO), and all agree that irradiated foods do not become radioactive and do not change their nutritional properties or organoleptic characteristics.· Not all foods can be subjected to irradiation, only some meats, fruits and vegetables, crustaceans, molluscs, spices and condiments.

· This technique is not accepted in all countries and must be applied in an external food irradiation plant.

· Requires expensive equipment

High pressure food preservation methods

Pascalization or pressurization

The technique is named after Blaise Pascal, a 17th century scientist who studied the effects of pressures applied to fluids in detail. It is based on subjecting a food to high hydrostatic pressure (HHP), affecting its cell membranes and the structure of some proteins. This process makes microorganisms inactive without altering the organoleptic quality or the nutrients of the product.

· It is a method of food preservation that does not require additives or preservatives.

· It does not change the organoleptic properties of food. The food’s flavor, texture and appearance are maintained.

· Not all foods can undergo this treatment. It works especially well in acidic foods, such as yogurt and fruit.
· Some foods treated with pascalization require storage at a controlled temperature.

· The application of high hydrostatic pressure (HHP) in a food product kills many microorganisms, but the spores are not destroyed.

· Food should be packaged in a flexible container so the pressure can be optimally transmitted. Glass jars or canning tins cannot be used.

Food preservation methods using chemical alterations

Pickled gherkins, one of the methods of food preservation using chemical alterations

These are very old techniques that have been used since prehistoric times to extend the shelf life of foods, help reduce their microbial load and slow down the chemical degradation rate of nutrients and organoleptic properties.

These methods are classified into two types, depending on whether the food is preserved in a dry or liquid medium.

  • In dry mediums:


Consists of applying smoke directly to food and thus prevent the proliferation of microorganisms thanks to the antiseptic properties of smoke and the effects of heat. Used mainly in sausages, cheeses, meats, fish, etc.


The food to be preserved is covered with a dry brine. Sometimes also with sugar to protect the exterior. This causes dehydration of the product and therefore prevents the proliferation of microorganisms. Used in the production of anchovies, dried hams or dried fish roe, among others.

  • In wet mediums:

The food is covered with different preservative liquids in order to slow or prevent the appearance or multiplication of microorganisms.


Liquid preparation made up of various ingredients such as oil, vinegar, spices, salt and aromatic herbs. It is applied cold, covering the raw food. The oil protects the food from the action of oxygen and the vinegar hinders the proliferation of microorganisms.

Pickling spice

Aqueous mixture, formed by three parts oil and one part vinegar, wine or other liquor, in which the submerged food is cooked. It is used mainly with meat, poultry, vegetables, fish and shellfish.


Consists of covering the food with wine and a base of vegetables such as onions, celery and carrots and aromatic herbs for a few hours, depending on the quantity and size of the product. Mostly used with fish or game.


Submerging the food in salt and vinegar. This acid medium suppresses the development of microorganisms. Usually used for raw or cooked vegetables: gherkins, onions, carrots, turnips, cabbage and garlic, as well as for various aromatic herbs.

· These are food preservation methods that require natural additives and preservatives.

· Foods preserved in dry media can last up to 2 years.
· Food preservation methods using chemical alterations change the taste, texture and appearance of food. They can also limit certain denominations such as ‘bio’ or ‘eco’.

· It is recommended to sterilize foods preserved in liquid media prior to marketing and, once the container is opened, they must be refrigerated and consumed shortly.

Food preservation methods using additives

So-called “food additives” are substances added to food to improve its color, texture, flavor or simply to preserve it for a longer period of time. They can be of natural origin, such as pectins, from plants, and agars, from algae; or of synthetic origin, all of which must be authorized for human consumption.


These prevent the chemical degradation of the food caused by heat, light and traces of pro-oxidant metals. They are used in fatty products such as margarines, mayonnaise, etc. A natural antioxidant commonly used in cooking preparations is ascorbic acid or vitamin C (naturally present in lemon juice).


They prevent the biological degradation of food by inactivating bacteria, yeast or fungi, or preventing or drastically reducing their growth. Commonly applied in meat preserves, bakery products, sauces, etc.

· They improve the flavor and appearance of the foods to which they are added.· Food preservation methods that incorporate additives and preservatives of artificial or natural origin, which for some consumers is an issue.

· Some additives or preservatives may be not tolerated by patients with certain pathologies, such as asthmatic or allergic people.

Food preservation methods based on atmospheric control

Tray with vacuum-packed fish, one of the methods of preserving food by controlling the atmosphere

These techniques seek to reduce the presence of substances that favor the deterioration of food or incorporate those that stop it within the container itself.

Vacuum packaging

Elimination of all the air inside the container in which the food is stored, such as with vacuum bags or trays. This treatment stops the oxidation processes and the multiplication of germs and prolongs the useful life of the product. Microorganisms that need oxygen to live (aerobic) cannot grow, but those that do not need oxygen (anaerobic) can.

Modified atmosphere packaging

This process focuses on creating a vacuum in the packaged food to then introduce a mixture of gases, mainly intended to eliminate oxygen or modify the percentage of gases that make up the air. The most commonly used gases are carbon dioxide (CO2) and nitrogen (N2). Carbon dioxide has a certain preservative power by itself, while nitrogen is an inert gas thatis preferrable than naturail air that contains oxygen and also acts as a “filler”, so that food is not squashed, as it is when using vacuum packaging.

A clear example of this practice are bags of potato chips, in which nitrogen is inserted, because in order to prevent the food from going rancid, the oxygen must be eliminated. And, therefore, a gas must be introduced that prevents the bag from becoming empty and the potato chips from being crushed.

This technique allows the product to be preserved in a fresh state, without chemical or thermal treatments, and without altering its organoleptic properties. Although over time, and depending on the evolution of the food, the atmosphere will change.

Products packaged in modified atmosphere which are not dry (like some snacks), must be kept refrigerated.

Controlled atmosphere packaging

It consists of creating a vacuum, but replacing the air with other gases whose composition we will keep constant over time through continuous control of the atmosphere. This system guarantees a long preservation of the product.

· These conservation techniques keep most of the organoleptic properties of the food unchanged and guarantee long shelf lives.· Methods of preserving food by controlling the atmosphere usually need to be supplemented by other methods, such as refrigeration or freezing.

· Requires expensive equipment

Important considerations when selecting the most suitable preservation method for the preparation of gourmet preserves and ready meals

When choosing which process is best, both for your premises and the food to be preserved, it is important that you make sure that the technique you are evaluating allows you to:

  • Guarantee the maximum useful life of the food preserved or, at least, a sufficient length.
  • Achieve minimal changes in the organoleptic and nutritional characteristics of the food.
  • Affordable to implement in your production process and business model.

Likewise, when choosing between one method or another, the requirements demanded by each method must be taken into account, such as the scope of application, the necessary equipment and machinery, storage spaces, distribution methods, etc.

With regard to gourmet preserves and ready meals, sterilization is the technique that provides the best results as it avoids cold chain distribution and very long best before dates. And we are not just saying that because we are the manufacturers of autoclaves used for the cooking, pasteurization or sterilization of gourmet preserves and ready meals, but because our customers confirm it. You can check it out for yourself, by visiting our success stories.

Why? Well, because sterilization ensures the total eradication of microorganisms and spores and, although it is true that it could lead to a decrease in the organoleptic characteristics of your product, that loss is very insignificant, especially if you sterilize with a TERRA Food-Tech autoclave®.

Likewise, working with an autoclave gives you the security of complying with hygiene and food safety regulations and avoiding possible health and public health risks. The traceability and auditability of each batch processing is guaranteed.

TERRA Food-Tech® autoclaves for artisan productions

Canned Virtute Naturae sterilized with the TERRA Food-Tech autoclave

Our vertical top-loading autoclaves have a capacity of 33 to 175 liters and are designed for entrepreneurs, restaurateurs, farmers and chefs that want to cook, pasteurize and/or sterilize all kinds of packaged preserves, canned food and ready meals.

In addition, the purchase of a TERRA Food-Tech® autoclave includes food consultancy and professional guidance service — we provide you with an initial guidance free of charge so that you can get started as soon as possible.

Likewise, to make it easier to estimate the viability and performance of your project, at TERRA Food-Tech® we provide a free online calculator for you to calculate the per cycle production capacity, i.e., the amount of containers that can be produced according to the type of recipient and the autoclave model.

If you are a small-business, a farmer, restaurateur or microentrepreneur, and you want to produce your own gourmet canned food and prepared dishes, don’t hesitate to use a professional autoclave to comply with applicable regulations and avoid jeopardizing your customers’ health.

For more information on thermal processing of food, such as pasteurization or sterilization, or to find out which autoclave best suits your business, contact our sales team. We will be happy to help you.

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