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:

Physical agents

Those external elements that directly impact and alter the external appearance of the preserved food:

Chemical agents

Which usually change internal aspects of food, for example, natural nutrients undergo chemical changes that can reduce their efficacy when consumed:

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

Refrigeration

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.

Freezing

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.

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High-temperature food preservation methods

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

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. This technique is used in jams, syrups, pickles, creams, soups, sauces and stews, among many other food forms.

Pasteurization

Unlike sterilization, pasteurization uses lower temperatures, below 100ºC, and the process does not completely eliminate microorganisms and spores. Above all, milk and its derivatives, flavored juices and beers, but also prepared dishes and sauces are pasteurized.

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Water content reduction as a food preservation method

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.

Concentration

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.

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Food preservation methods based on irradiation

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.

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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.

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Food preservation methods 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:

Smoking

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.

Salting

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.

Dressing

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.

Marinating

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.

Pickling

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.

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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.

Antioxidants

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).

Conservatives

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.

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Food preservation methods based on atmospheric control

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.

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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.

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 itcould 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

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 includesfood 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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