Food Safety Milestones Part 2: Food Preservation in the Industrial Age

In Part 1 of our mini-series on the milestones of food safety, we surveyed the history of food preservation techniques prior to the advent of the Industrial and Scientific Revolutions. In this post, Part 2 will look at five essential technical advances in food preservation discovered primarily by scientists and developed by inventors: canning, pasteurization, refrigeration, freezing, and thermometry.

Canning

Canning is the first major industrial form of food preservation. In simple terms, it’s the process by which foods are sealed in jars or cans and heated to a temperature that destroys microorganisms and inactivates enzymes. This heating (and later cooling) forms a vacuum that prevents other microorganisms from contaminating the food as long as the seal remains unbroken.

In the early 1800s, during the Napoleonic wars, the French government offered a cash award of 12,000 francs to any inventor who could devise a cheap and effective method of preserving large amounts of food to feed armies with regular supplies during winter months. In 1809, Nicolas Appert, a French confectioner and brewer, won the prize for discovering that the application of heat to food in sealed glass bottles preserved the food from deterioration.

Appert's principles were successfully adopted by the French Navy for meat, vegetables, fruit, and milk. Eventually, his methods spread throughout England, where Peter Durand improved the process using tin cans in 1810; and then to the United States, where Robert Ayars established the first canning factory in New York City in 1812. By the late 19th century, canning companies such as Underwood, Nestlé, and Heinz developed new markets for civilian urban populations between wars, competing with each other using lower prices, novel products, and innovative printed labels. Canning also moved into the domestic kitchen, where homemakers could preserve their own jams, pickles, and soups.

Pasteurization

Although Appert had devised a successful method to preserve foods, he did not understand why it worked. It was not until 1864, when Louis Pasteur discovered pasteurization, that the cause-and-effect connection between microbes and foodborne illness became clear. Whereas Appert had believed the lack of air within the sealed vacuum killed pathogens, Pasteur proved that it was the heat itself.

Today, pasteurization is used widely in the dairy industry and other food processing industries (such as juice, vinegar, eggs, and nuts) to achieve both food preservation and food safety for packaged and unpackaged products. Typically, one of three processes is involved:

• High Temperature Short Time (HTST): the most common form of pasteurization that uses metal plates and hot water to raise temperatures to at least 161° F for not less than 15 seconds, followed by rapid cooling
• Ultra Pasteurization (UP): requires that foods be heated to not less than 280° for two seconds, resulting in a product with a longer shelf life, but still requiring refrigeration
• Ultra High Temperature (UHT): involves heating with commercially sterile equipment and filling it under aseptic conditions into hermetically sealed packaging that is “shelf stable” with no need for refrigeration

Refrigeration

Despite innovations like UHT, refrigeration remains the most popular and prevalent form of industrial food preservation, since it is best at maintaining food quality, including freshness, texture, and nutritional value. Briefly, the process removes heat from a low-temperature reservoir and transfers it to a high-temperature reservoir, traditionally by mechanical means, but also by magnetism, electricity and laser, among others.

Historically, the desire for artificial refrigeration arose from the combination of new forms of common knowledge: the ability of cold to keep food safe, Pasteur’s discovery of germs and bacteria as the cause of foodborne illness, and the efficiency of industrial processes such as canning that allowed all kinds of food to be preserved and transferred anywhere over long distances.

Many scientists and inventors contributed to the development of refrigeration, including such well-known figures as Benjamin Franklin and Michael Faraday. But perhaps the most important was Alexander C. Twining, who in the mid-19th century experimented with commercial refrigerants that would eventually be used for both trains and meat packing. Beginning in the 1860s, refrigerated train cars transported food around the country, requiring new standards in food processing and the creation of huge, centralized processing plants.

As society rapidly transformed from a rural, agricultural to an urban, industrial one, refrigeration increased the availability of fresh beef and other meats, and in turn, the taste for it at the grocery store and at home. The result was the invention of the modern home refrigerator that supplanted iceboxes in the 1930s.

Freezing

Freezing keeps food safe by slowing the movement of molecules, causing microorganisms – bacteria, yeasts and molds – that cause both food spoilage and foodborne illness to enter a dormant stage, thereby preventing their continued growth. Two processes dominate the food industry:

• Mechanical: the most popular form of freezing, mechanical systems circulate a refrigerant, usually ammonia, which withdraws heat from the food product. This heat is then transferred to a condenser and dissipated into air or water.
• Cryogenic: a more recent development, also referred to as “flash freezing,” cryogenic systems apply liquid nitrogen or solid carbon dioxide directly to the food product.

Clarence Birdseye is the most important figure in the history of commercial frozen food. In 1928, he invented the double belt freezer, the forerunner of modern freezing technology; and two years later, he introduced a line of frozen foods to the public, including vegetables, fruits, fish fillets, 18 cuts of meat, and even Blue Point oysters.

The advent of WWII guaranteed the success of frozen foods. When the U.S. government placed controls on canners to conserve wartime metal, retail grocers were more than happy to fill their empty shelves with new frozen products to replace the dearth of canned goods. Food manufacturers began to innovate new forms of highly successful frozen products, such as concentrated orange juice, breaded fish sticks, and TV dinners.

The introduction of the microwave accelerated the marketing of frozen meals, which soon became popular as much for their convenience as their safety. Of course, microwaves increased the danger that pathogens deactivated (but not killed) by the freezing process could once again become active if the frozen food is not thawed and cooked within safe temperature ranges.

Thermometry

Which brings us to the final scientific milestone: the invention of thermometers. Whether the process is canning, refrigerating or freezing, the only sure method to know that foods are being processed at safe temperatures is the science of thermometry. Although Greek philosophers were aware of some basic principles of the thermometer two thousand years ago, only with the Scientific Revolution was the modern thermometer invented. Highlights of this long development process include:

• Christiaan Huygens first suggested using the melting and boiling points of water as standards of temperature measurement (1665).
• Daniel Gabriel Fahrenheit invented the first reliable mercury thermometer (1724) and proposed the temperature scale still used in the United States.
• Anders Celsius proposed a universal scale with 100 degrees (1742), today commonly used throughout the world.
• Thomson Kelvin updated the centigrade scale (1848) based on the theoretical "absolute zero" where all molecular activity stops, now the official International Temperature Scale, as of 1990.

In the last 150 years, scientists discovered other physical properties that respond reliably to the application of heat and cold besides the expansion and contraction of liquids inside a tube:

• Dial thermometers use the expansion and contraction of metal.
• Digital thermometers use the effects of heat and cold on the speed or flow of electronic circuits.
• Infrared thermometers measure the emission of infrared radiation.
• Still other thermometers use physical phenomena such as sound waves, photoluminescence, fluorescence, magnetism, and gamma rays.

At SmartSense, we understand the science behind these incredible inventions, and use it to create a temperature monitoring system that best ensures your heating, cooling and freezing units and equipment are working continuously to keep your food products safe for consumers.

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