Preservation Methods

Preserving food means slowing down and stopping the reactions and microbial growth that deteriorate it. No domestic method turns food into indefinite preservation: the raw ingredients, hygiene, process, packaging, and storage temperature form a single system.

What Controls Preservation

Microorganisms need favorable conditions to grow. Preservation methods act by reducing temperature, removing available water, increasing acidity, applying heat, or creating an environment that is less favorable. Often, multiple barriers are combined.

Safe Preservation, Proven Recipes

In home canning, it's not advisable to improvise proportions, times, or processes. Acidity and type of food determine if a water bath is sufficient or if pressure treatment is needed. Always use validated procedures.

Preservation by Cold

Refrigeration

Slows microbial growth, but does not stop it completely. Store raw and cooked foods separately, use sealed containers, respect the date and instructions on the packaging, and place what should be consumed first in front.

Freezing

Stops the growth of many microorganisms while maintaining cold, but does not eliminate them. Freeze in portions, label with content and date, protect from air, and avoid repeated temperature changes.

Thawing

Do it in the refrigerator, in the microwave if it will be cooked immediately or as part of cooking when the food allows it. Avoid leaving perishable products at room temperature for hours.

Quick Cooling or Rapid Cooling

Consists of rapidly lowering the temperature of cooked food. At home, divide large portions into low containers or portions to cool before refrigerating.

Preservation by Heat

Ultraviolet Light

Applies a moderate thermal treatment to reduce microorganisms and extend shelf life. It does not always equate to sterilization: many pasteurized products need to be kept refrigerated.

Boiling

Uses higher temperatures to achieve a stable product for a longer time. At home, requires equipment, control, and a process adapted to the food. Acidic foods should not be treated as jams or pickles.

Marie Pasteurization for Acidic Foods

Used with validated recipes for fruits, jams, pickles, and other sufficiently acidic foods. The jar size, filling, closure, altitude, and time are part of the process.

Pressure Canning

The procedure indicated for many low-acid canned foods, such as vegetables, meats, poultry, or mixes containing them. A common domestic pressure cooker should not be assumed equivalent to a validated pressure canning equipment.

Preservation by Reducing Available Water

Drying

Removes moisture through air, gentle heat, and circulation. Uniform slicing is essential. The food must be completely dry and protected from moisture, heat, and light.

Salting and Fermentation

Salt draws out moisture and modifies the microbial environment. Fish, meat, and vegetables require specific proportions, temperatures, and times; large pieces do not suffice to salt the surface.

Preservation with Sugar

High concentrations of sugar reduce available moisture in jams, jellies, and confit fruits. Reducing sugar in a validated recipe can change both texture and stability.

Dry Ice

Freezes the food and extracts water in a vacuum. Maintains good shape and aromas, but requires specific equipment and is not equivalent to freezing or drying in a domestic oven.

Acidity, Pickling, and Fermentation

Pickling

The food is preserved in an acidic medium, typically vinegar or acidified saltwater. Use vinegar with known acidity and do not alter the relationship between food, water, and acid in a validated recipe without criteria.

Lactic Acid Fermentation

Beneficial microorganisms transform sugars and generate acid. Sauerkraut, kimchi, or some olives follow this principle. The proportion of salt, immersion, temperature, and cleanliness control the process.

Alcoholic Fermentation

Yeasts convert sugars into alcohol and carbon dioxide. Used in bread, wine, beer, and other beverages. Each elaboration requires specific yeast strains, temperature, and control.

Other Methods and Their Limits

Vacuum Sealing

Reduces oxygen and protects against oxidation and desiccation, but does not sterilize. Perishable foods vacuum-sealed still need refrigeration and controlled shelf life.

Canning in Oil

The oil limits contact with air, but does not eliminate microorganisms or guarantee safety at room temperature. Homemade preparations with garlic, herbs, vegetables, or fish in oil should follow a safe recipe and, when appropriate, be kept refrigerated.

Drying

Provides aromatic compounds and can contribute to preservation when combined with salting, drying, or cold. Light smoking alone is primarily considered a flavor technique.

Which Method to Choose

Need	Method	Key Control
Consume in a few days	Refrigeration	Constant cold, sealed container, and date
Store portions for longer periods	Freezing	Proper packaging, labeling, and safe thawing
Fruit for spreading	Validated jam recipe	Proportion, acidity, treatment, and closure
Acidic vegetables	Validated pickling	Known acidity and exact proportions
Herbs or dried fruit	Drying	Uniform drying and moisture-free packaging
Vegetables, meat, or fish of low acidity	Validated pressure canning	Equipment, pressure, and specific times

Packaging, Labeling, and Warning Signals

• Wash and inspect containers; use compatible and good condition lids.
• Label with name, date of preparation, and, if applicable, date of opening.
• Rotate the pantry: the first in should be the first out.
• Discard sealed containers with bulges, leaks, broken closures, unexpected foam, or content that releases pressure.
• Do not taste a suspicious can to decide if it is safe: some toxins are not detected by smell or taste.