Food preservation has played an important role in the survival of humanity. It is also a good way to prevent food being wasted. Here we discuss some of the most common food preservation techniques used historically and in modern times.
Artificial food additives
Adding preservatives to food is one of the most modern ways of preserving food. The additives are either antimicrobial, to delay, inhibit or prevent microbial growth, or antioxidant, which inhibits the oxidation of food and prevents spoilage. Common antimicrobial preservatives include calcium propionate, sodium nitrate, sodium nitrite, sulphites and ethylenediaminetetraacetic acid (EDTA). Antioxidants include butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT).
Curing is a method of preserving meat by drying, salting and smoking. People were drying meat as early as 12 000 BC. Later, smoking and salting techniques were used, which improved the drying process by adding antimicrobial agents that helped with preservation. Today nitrites are used to cure meat. Some examples of cured meat are Parma ham, salami and biltong.
Cooling and freezing
Cooling food delays the activity of the microorganisms and enzymes that cause food to rot. Before refrigerators and deep freezers were available, food was kept cool in cellars and iceboxes. In colder countries cellars are still popular places to keep root vegetables and wine cool, but generally, freezing meat and vegetables is now the most common form of preservation.
Boiling and pasteurisation
Heat kills microorganisms in food and prolongs its shelf life. Throughout the ages, heating through boiling has been used as a form of preservation. An ancient example is the perpetual stew, common in the Middle Ages. A perpetual stew simmers in a pot that is never, or rarely, emptied of all its contents; ingredients are continuously added and liquid is replenished as necessary.
A more modern technique that uses boiling is pasteurisation, which is applied to dairy products. This technique was invented by Louis Pasteur, a French chemist, in 1862. The milk is heated at approximately 70°C for 15 to 30 seconds to kill the bacteria, and is then rapidly cooled to 10°C to prevent the remaining bacteria from growing. It is then stored in containers.
Burial, jugging and confit
Burial, jugging and confit are very old ways of preserving food and are not widely used today.
The burial of food preserves it by limiting exposure to light and oxygen and providing a cool temperature. Burial was often combined with salting or fermentation. Common food types that were buried included fish, such as gravlax (cured salmon), dairy products, such as bog butter buried in peat bogs, and vegetables.
Jugging was a popular method of preserving meat until the middle of the 20th century. Meat, usually cut into pieces, would be placed in a tightly-sealed earthenware jug with brine or gravy, and stewed. Red wine and/or animal blood was sometimes added to the cooking liquid.
A similar way of preserving meat, common in Europe and still used in France, is the confit method, where the meat is preserved by salting it, cooking it in animal fat at or near 100°C, and storing it immersed in the fat. The meat was often stored in a cold cellar or buried in the ground.
Canning is widely used to preserve a variety of food, from meat and fish to vegetables and fruit. It was invented by the French confectioner Nicolas Appert, and by 1806 it was used by the French Navy to preserve meat, fruit, vegetables and even milk, for soldiers. Canning involves cooking food, sealing it in sterilised cans or jars, and boiling the containers to kill or weaken any remaining bacteria.
Cheese, wine and beer is made using specific microorganisms that combat spoilage by the microbial conversion of starch and sugars into alcohol, making this a good preservation technique. Fermentation can also make food more nutritious and palatable. In the Middle Ages, it was more dangerous to drink water than to drink beer or wine, because water contained pathogens that were killed during the brewing and fermentation process of beer and wine.
Freeze drying is a low temperature dehydration process during which a product is frozen, the pressure is lowered, and the ice is removed through sublimation. It results in a high-quality product because of the low temperature used in processing. The original shape of the product is maintained, and the quality of the rehydrated product is excellent.
High-pressure processing (HPP) is a modern food preservation technique that processes food by applying pressure in a contained space. It allows food to retain its fresh appearance, flavour, texture and nutrients while inactivating harmful microorganisms and slowing spoilage. The process has been popularly used since 2005 for various products, including orange juice, guacamole and processed meats.
Irradiation exposes food to ionising radiation that kills microorganisms. It also reduces the ripening and spoiling of fruit. This method allows lower quality or contaminated foods to be rendered marketable and is commonly used on herbs and spices to prolong shelf life.
Pickling preserves food by storing it in a liquid and can be classified into two categories: chemical pickling and fermentation pickling.
In chemical pickling, the food is placed in an edible liquid that inhibits or kills bacteria and other microorganisms. Typical pickling agents include brine (high in salt), vinegar, alcohol and vegetable oil. Many chemical pickling processes also involve heating or boiling so the food being preserved becomes saturated with the pickling agent. Cucumbers, peppers, corned beef, herring, eggs and mixed vegetables are some commonly pickled foods.
In fermentation pickling, bacteria in the liquid produce organic acids that act as preservation agents, typically by a process that produces lactic acid through the presence of lactobacillus. Sauerkraut and kimchi are made in this way.
Sugaring and jellying
Using sugar as a preservative is one of the oldest food preservation techniques and is still used today. Sugar draws water from microorganisms that dehydrates and eventually kills them. It was commonplace to store fruit in honey until sugarcane was brought to Europe.
Sugar is often used to preserve fruit, either in syrup or in a crystallised form. Fruit, such as peaches and apricots, is commonly boiled in sugar syrup and preserved in jars. Alternatively, fruit is cooked in sugar until it crystallises, after which it is stored dry. This method is most often used for the skins of citrus fruit and ginger.
Sugaring can also be used to produce jam and jelly. Jellying involves cooking fruit until it forms a gel. The only difference between jelly and jam is that all fruit pips are removed in the making of jelly.
Vacuum-packed food is stored in an airtight bag in which bacteria cannot survive due to the lack of oxygen. This method is used for a wide range of food products, from nuts to cheese and meat. – Ursula Human, FarmBiz