Food Preservation

Fermented Foods

Fermentation is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using microorganisms.

Learning Objectives

Describe the process of fermentation and its use in the food industry

Key Takeaways

Key Points

  • Fermentation usually implies that the action of microorganisms is desirable.
  • Fermentation produces alcoholic beverages such as wine, beer, and cider.
  • Fermentation is also employed in the leavening of bread and the production of dairy products.

Key Terms

  • fermentation: Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions.
  • carbohydrates: A major class of foods that includes sugars and starches.
  • microorganisms: A microorganism or microbe is a microscopic organism that comprises either a single cell (unicellular), cell clusters, or multicellular relatively complex organisms.
  • oligodynamic action: that is active in small quantities; used especially to describe the sterilizing effect of some heavy metals against bacteria

Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol. The science of fermentation is also known as zymology or zymurgy.

Historically, when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that the fermentation was catalyzed by a vital force, called “ferments,” within the yeast cells. The “ferments” were thought to function only within living organisms. “Alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells,” he wrote.

Fermentation usually implies that the action of microorganisms is desirable. This process is used to produce alcoholic beverages such as wine, beer, and cider. Fermentation is also employed in the leavening of bread (CO2 produced by yeast activity); in preservation techniques to produce lactic acid in sour foods such as sauerkraut, dry sausages, kimchi, and yogurt; and in the pickling of foods with vinegar (acetic acid).

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Beer: This is beer fermenting at a brewery.

Food fermentation has been said to serve five main purposes:

  1. Enrichment of the diet through development of a diversity of flavors, aromas, and textures in food substrates.
  2. Preservation of substantial amounts of food through lactic acid, alcohol, acetic acid, and alkaline fermentations.
  3. Biological enrichment of food substrates with protein, essential amino acids, essential fatty acids, and vitamins.
  4. Elimination of antinutrients.
  5. A decrease in cooking time and fuel requirement.

Food Spoilage by Microbes

Food spoilage is the process in which food deteriorates to the point it is not edible to humans or its quality of edibility becomes reduced.

Learning Objectives

Describe the process of food spoilage

Key Takeaways

Key Points

  • Bacteria can cause food spoilage by breaking down the food, producing acids or other waste products during this process.
  • Harvested crops decompose from the moment they are harvested due to attacks from microorganisms.
  • Signs of food spoilage may include an appearance different from the food in its fresh form, such as a change in color, a change in texture, an unpleasant odor, or an undesirable taste.

Key Terms

  • food spoilage: Food spoilage is the process in which food deteriorates to the point that it is not edible to humans or its quality of edibility becomes reduced.
  • microorganisms: A microorganism or microbe is a microscopic organism that comprises either a single cell (unicellular), cell clusters, or multicellular relatively complex organisms.
  • bacteria: A type, species, or strain of bacterium.

Food spoilage is the process in which food deteriorates to the point that it is not edible to humans or its quality of edibility becomes reduced. Various external forces are responsible for the spoilage of food. Food that is capable of spoiling is referred to as perishable food.

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Food Spoilage: This apple has decomposed to the point that it is unappealing for humans to eat.

Harvested crops decompose from the moment they are harvested due to attacks from microorganisms.

Various bacteria can be responsible for the spoilage of food. When bacteria breaks down the food, acids and other waste products are created in the process. While the bacteria itself may or may not be harmful, the waste products may be unpleasant to taste or may even be harmful to one’s health.

Yeasts can be responsible for the decomposition of food with a high sugar content. The same effect is useful in the production of various types of food and beverages, such as bread, yogurt, cider, and alcoholic beverages.

Signs of food spoilage may include an appearance different from the food in its fresh form, such as a change in color, a change in texture, an unpleasant odor, or an undesirable taste. The item may become softer than normal. If mold occurs, it is often visible externally on the item.

Some spoiled foods are harmless to eat, and may simply be diminished in quality. But foods exhibiting certain types of spoilage may be harmful to consume. Uncooked or under-cooked animal flesh that spoils is typically quite toxic, and consumption can result in serious illness or death. The toxic effects from consuming spoiled food are known colloquially as “food poisoning”, and more properly as “foodborne illness. ”

Food Preservation

Food preservation is the process of treating food to stop or slow down spoilage, loss of quality, edibility, or nutritional value.

Learning Objectives

Describe how food preservation processes stop or slow down food spoilage thus allowing for longer food storage

Key Takeaways

Key Points

  • Preservation usually involves preventing the growth of bacteria, fungi (such as yeasts), and other microorganisms, as well as retarding the oxidation of fats which cause rancidity.
  • A number of methods of prevention can be used that can either totally prevent, delay, or otherwise reduce food spoilage.
  • Maintaining or creating nutritional value, texture, and flavor is an important aspect of food preservation.

Key Terms

  • Preservation: Food preservation is the process of treating and handling food to stop or slow down food spoilage, loss of quality, edibility, or nutritional value and thus allow for longer food storage.
  • microorganisms: A microorganism or microbe is a microscopic organism that comprises either a single cell (unicellular), cell clusters, or multicellular relatively complex organisms.
  • food spoilage: Spoilage is the process in which food deteriorates to the point that it is not edible to humans or its quality of edibility becomes reduced.

Food Preservation

Food preservation is the process of treating and handling food to stop or slow down food spoilage, loss of quality, edibility, or nutritional value and thus allow for longer food storage.

Preservation usually involves preventing the growth of bacteria, fungi (such as yeasts), and other microorganisms, as well as retarding the oxidation of fats which cause rancidity.

Methods of Food Preservation

A number of methods of prevention can be used that can either totally prevent, delay, or otherwise reduce food spoilage. Preservatives can expand the shelf life of food and can lengthen the time long enough for it to be harvested, processed, sold, and kept in the consumer’s home for a reasonable length of time.

Maintaining or creating nutritional value, texture and flavor is an important aspect of food preservation, although, historically, some methods drastically altered the character of the food being preserved. In many cases these changes have now come to be seen as desirable qualities, as with cheese, yogurt, and pickled onions.

Drying is one of the most ancient food preservation techniques, which reduces water activity sufficiently to prevent bacterial growth.

Refrigeration preserves food by slowing down the growth and reproduction of microorganisms and the action of enzymes which cause food to rot.

Freezing is also one of the most commonly used processes for preserving a very wide range of food including prepared foodstuffs which would not have required freezing in their unprepared state.

Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag or bottle. The vacuum environment strips bacteria of oxygen needed for survival, thereby slowing spoiling. Vacuum-packing is commonly used for storing nuts to reduce the loss of flavor from oxidation.

Salting or curing draws moisture from the meat through a process of osmosis. Meat is cured with salt or sugar, or a combination of the two. Nitrates and nitrites are also often used to cure meat and contribute to the characteristic pink color, as well as inhibition of Clostridium botulinum.

Sugar is used to preserve fruits, either in syrup with fruit such as apples, pears, peaches, apricots, plums, or in crystallized form where the preserved material is cooked in sugar to the point of crystallisation and the resultant product is then stored dry. This method is used for the skins of citrus fruit (candied peel), angelica, and ginger. A modification of this process produces glacé fruit such as glacé cherries where the fruit is preserved in sugar but is then extracted from the syrup and sold, the preservation being maintained by the sugar content of the fruit and the superficial coating of syrup. The use of sugar is often combined with alcohol for preservation of luxury products such as fruit in brandy or other spirits. These should not be confused with fruit flavored spirits such as cherry brandy.

Smoking is used to lengthen the shelf life of perishable food items. This effect is achieved by exposing the food to smoke from burning plant materials such as wood. Most commonly subjected to this method of food preservation are meats and fish that have undergone curing. Fruits and vegetables like paprika, cheeses, spices, and ingredients for making drinks such as malt and tea leaves are also smoked, but mainly for cooking or flavoring them. It is one of the oldest food preservation methods, which probably arose after the development of cooking with fire.

Preservative food additives can be antimicrobial. These inhibit the growth of bacteria or fungi, including mold, or antioxidant, such as oxygen absorbers, which inhibit the oxidation of food constituents. Common antimicrobial preservatives include calcium propionate, sodium nitrate, sodium nitrite, sulfites (sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, etc.), and disodium EDTA. Antioxidants include BHA and BHT. Other preservatives include formaldehyde (usually in solution), glutaraldehyde (kills insects), ethanol, and methylchloroisothiazolinone.

Pickling is a method of preserving food in an edible anti-microbial liquid. Pickling can be broadly categorized into two categories: chemical pickling and fermentation pickling.

Canning involves cooking food, sealing it in sterile cans or jars, and boiling the containers to kill or weaken any remaining bacteria as a form of sterilization. Foods have varying degrees of natural protection against spoilage and may require that the final step occur in a pressure cooker. High-acid fruits like strawberries require no preservatives to can and only a short boiling cycle, whereas marginal fruits such as tomatoes require longer boiling and addition of other acidic elements. Low acid foods, such as vegetables and meats require pressure canning. Food preserved by canning or bottling is at immediate risk of spoilage once the can or bottle has been opened.

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Preserved Food: Canning food is one method of food preservation.

Other forms of preservation can include: jellying, jugging, irradiation, pulsed electric field processing, modified atmosphere, high pressure, burial in the ground, and biopreservation.