Unit Content
The content is organized into three sections that examine the methods people used to preserve food before refrigeration: salting and brining, pickling, and smoking. The first section, "Salt and Survival," explores the historical importance of salt preservation in Colonial America while addressing the essential question, "How does salt help keep food safe to eat?" Students investigate both the historical significance of salt and the scientific principles that make it an effective preservative, including osmosis and diffusion as they relate to dry salting and brining. The section concludes with two hands-on investigations that reinforce these concepts. In the first activity, students compare cucumbers treated with salt to untreated cucumbers, recording observations after 30 minutes, 3 hours, and 24 hours to observe the effects of dry salting. In the second activity, students investigate the effects of different salt concentrations by placing apple slices in brines with varying levels of salinity. Together, these investigations allow students to apply scientific concepts to historical food preservation practices while encouraging them to consider the challenges faced by European colonists during the transatlantic voyage and the early colonial period.
The second section, "Preserving Through Pickling," explores the cultural traditions and scientific principles associated with pickling while addressing the essential question, "How can changing the environment around food prevent spoilage?" Students investigate the chemical processes underlying pickling and are introduced to fermentation while examining how these preservation methods were used differently by European colonists and Eastern Native American communities. Building on the concepts introduced in the previous section, students apply their understanding of osmosis and diffusion to distinguish between brining and pickling and to explain the chemical changes that occur during pickling. They then prepare quick pickles and observe how the preservation process changes food over time by documenting differences in appearance, texture, smell, and taste and comparing pickled cucumbers with fresh samples. To further explore the science of preservation, students measure and compare the pH of water, vinegar, and the finished pickling solution, allowing them to investigate how increasing acidity inhibits the growth of many microorganisms responsible for food spoilage.
The final section, "Up in Smoke," explores smoking as a preservation method while addressing the essential question, "Why does smoke help preserve food?" Students investigate how Native American communities and colonial societies used smokehouses and other smoking techniques to extend the shelf life of food while exploring the scientific principles behind dehydration and the antimicrobial properties of smoke. As a hands-on extension, students construct a small-scale model of a colonial smokehouse using basic classroom materials, such as cardboard boxes, craft sticks, paper, and string. Through this model, students visualize the structure and function of a smokehouse by identifying the location of the fire source, where food would be suspended, and how smoke would circulate throughout the space.
Throughout the unit, students connect historical food preservation practices to scientific principles while examining how geography, cultural traditions, and available resources influenced the methods different communities developed. Together, these sections address the overarching question: "How did food preservation help people survive, adapt, and build communities in early America?"
Salt and Survival
Salt may seem like a simple ingredient, but it is a fascinating chemical compound with significant historical importance. In chemistry, the term salt refers to any ionic compound composed of positively and negatively charged ions. The salt commonly used in cooking is sodium chloride (NaCl), which is formed from sodium (Na⁺) and chloride (Cl⁻) ions. This essential nutrient has played a significant role throughout human history, not only as a dietary necessity but also as a valuable resource for preservation, trade, and cultural practices.
Archaeological evidence suggests that during the early Neolithic Period (6050–5500 BC), people were producing salt by boiling mineral-rich spring water in what is now Romania.[2] Although researchers cannot determine with certainty whether this early salt production was used for food preservation, livestock, ritual practices, trade, or other purposes, the discovery demonstrates that communities developed methods for obtaining and utilizing salt thousands of years ago. The ancient Egyptians and other civilizations of the Fertile Crescent are among the earliest societies credited with intentionally using salt to preserve food.[3] This innovation transformed food storage practices by extending the usability of perishable foods and allowing communities to store resources for future needs.
Salt preserves food by drawing moisture away from tissues, reducing the amount of water available for microbial growth. By creating conditions that inhibit many spoilage-causing microorganisms, salt preservation allowed communities to better withstand periods of scarcity, travel greater distances, participate in trade, and explore new regions without relying on a constant supply of fresh food. In addition to dry salting, these civilizations also preserved foods through brining, a process that involves immersing food in a saltwater solution.
For colonists immigrating to North America, salt was an essential resource for food preservation. It was transported alongside other necessities, and natural salt sources were sought soon after settlement.4 One of the simplest preservation techniques described by Oliver was lightly salting the exterior of meat, a process known as corning. Depending on environmental conditions, particularly temperature, this method could extend the storage life of meat for approximately one week, with colder conditions allowing for longer preservation. In general, the longer meat remained in contact with salt, the longer it could be stored safely. Colonists also practiced dry salting by combining salt with brown sugar and saltpeter before placing the meat into a vessel known as a powdering tub.[4] The tub allowed the meat to be rotated periodically, ensuring that the curing mixture coated the entire surface before the meat was packed into wooden barrels for storage. A related preservation method involved creating a concentrated brine by boiling water with salt, brown sugar, and saltpeter and then pouring the solution over the meat in barrels.[5]
Historical sources sometimes use the terms dry salting, brining, and pickling differently than they are defined today. For example, William B. Dick’s Encyclopedia of Practical Receipts and Processes describes dry salting and brining as using similar ingredients but distinguishes between them based on whether the meat remains submerged in the liquid.[6] According to this source, if the brine is drained away after salting, the process is considered dry salting; if the meat remains immersed in the brine, it is referred to as being pickled.[7] In this unit, however, brining and pickling are distinguished based on modern food preservation terminology: brining refers to preservation in a saltwater solution, while pickling refers to preservation through an acidic environment, typically using vinegar or fermentation-produced acids. The pickling process and its scientific principles are discussed in greater detail in the following section. Both dry curing and brining preserved meat by creating a high-salt environment that reduced the availability of water needed for microbial growth, thereby slowing spoilage and extending storage life. Although meat was the most commonly preserved food using salt during the colonial period, historical cookbooks also provide evidence that this practice extended to some vegetables, including cucumbers, green beans, and peas.[8] Hannah Glasse’s The Art of Cookery Made Plain and Easy, first published in 1747, was one of the most influential cookbooks available to American colonists and included recipes for preparing preserved foods.
Salted meats were not universally adopted among Indigenous communities. In Michael Wise’s Native Foods: Agriculture, Indigeneity, and Settler Colonialism in American History, he notes that many Eastern Woodland Native communities preferred traditional preservation practices, such as drying and smoking meat, rather than adopting salted meats introduced through colonial foodways. These preservation methods reflected Indigenous knowledge systems and adaptations to local environments and resources, which will be explored in a later section of this unit.
Osmosis and Diffusion
Although both methods rely on salt, dry salting and brining affect food differently. How is this possible? Before explaining how osmosis functions in both dry salting and brining, it is helpful to first review the structure of a cell and the processes involved. For simplicity, this discussion will focus on a muscle (meat) cell, although the same principles apply to many other organic cells. A muscle cell is "a long cylindrical fiber of protein and liquid containing dissolved substances, all encased in a membrane that allows water molecules to pass through”.[9] The cell membrane is selectively permeable, meaning it allows some substances to move across it more easily than others. One of the fundamental principles of chemistry is that systems naturally move toward equilibrium, or balance. In the context of osmosis, this means balancing the concentration of water on both sides of the cell membrane. When meat is submerged in a liquid, such as water or in this case, a brine, water molecules move across the cell membrane in response to differences in water concentration. If there is a higher concentration of water outside the cell than inside, water moves into the cell in an attempt to equalize the concentration on both sides of the membrane. This movement of water across a selectively permeable membrane is called osmosis.
At first glance, it may seem as though water is the only substance involved in this process, but salt also plays an essential role. Because a brine contains a much higher concentration of dissolved salt than the meat itself, salt ions also move across the cell membrane. Unlike the movement of water, however, the movement of salt ions is not osmosis; it is a process known as diffusion, the movement of dissolved particles from an area of higher concentration to an area of lower concentration. As salt diffuses into the muscle cells, it interacts with muscle proteins, causing them to partially unwind and increasing their ability to bind and retain water.[10] As a result, properly brined meat extends its shelf life and is often juicier and more tender after cooking.
Dry salting relies on the same scientific principles as brining but creates the concentration gradient in a different way. Instead of placing meat in a saltwater solution, dry salting applies salt directly to the surface of the food. This creates a highly concentrated environment outside the cells, causing water to move out of the meat through osmosis. As moisture leaves the cells, it dissolves the salt on the surface and creates a concentrated brine that surrounds the food. Over time, salt ions diffuse into the tissue while the overall amount of available water decreases, creating conditions that slow the growth of many spoilage microorganisms. The primary difference between dry salting and brining is the way salt and water move during the preservation process. In brining, the food begins surrounded by a liquid solution, allowing salt ions to gradually diffuse inward while water movement depends on the concentration of the surrounding solution. In dry salting, the food itself releases moisture to create the salty environment needed for preservation. Both methods rely on salt’s ability to alter the movement of water and create conditions that inhibit microbial growth, but they achieve this through different pathways. Although salt does not eliminate all microorganisms, it creates an environment that makes it difficult for many spoilage-causing microbes to grow and reproduce. This process is known as bacteriostasis, meaning the inhibition or slowing of bacterial growth. By drawing moisture away from food and reducing the amount of water available for microbial activity, salt preservation slows spoilage and extends the shelf life of perishable foods. The combined effects of osmosis, diffusion, and reduced water availability explain why dry salting and brining remained valuable preservation techniques for communities before refrigeration.
Preserving Through Pickling
For the purposes of this curriculum unit, pickling is defined as the preservation of food through the use of vinegar or other acidic solutions that inhibit the growth of spoilage-causing bacteria. It is important to note that while they achieve the same results, “pickling relies on an acidic liquid like vinegar and heating to achieve the end result, which is a sour flavor and longer shelf life. Fermentation, on the other hand, works because of the reaction between the sugars and bacteria that are naturally present in the food”.[11] According to a historical timeline published by the New York Food Museum, archaeological and anthropological evidence suggests that the Mesopotamians began pickling foods as early as 2400 BCE.[12] The timeline also illustrates the enduring cultural significance of pickled foods throughout history, noting that figures such as Julius Caesar, Cleopatra, and Queen Elizabeth I praised their perceived medicinal or health benefits. The word pickle also expanded beyond its culinary meaning, with Shakespeare among the early writers to use it metaphorically.[13]
By 1659, Dutch settlers in New Amsterdam (present-day New York City) were cultivating large cucumber fields and selling pickled cucumbers throughout the city. These practices contributed to a long-standing tradition of pickle production in North America, influencing the development of the country’s pickle industry long before the United States was established.[14] Evidence from colonial cookbooks also demonstrates the careful attention early Americans gave to the preparation and storage of pickled foods. In Hannah Glasse’s The Art of Cookery Made Plain and Easy, first published in 1747, she provides detailed instructions for properly storing pickled foods and preventing spoilage:
“Always use Stone-Jars for all Sorts of Pickles that require hot Pickle to them. The first Charge is the least; or these not only lasts longer, but keep the Pickle better; for Vinegar and Salt will penetrate through all earthen Vesl'els, Stone and Glass is the only thing to keep Pickles in. Be sure never to put your Hands in to take Pickles out, it will soon spoil it. The best Way is to every Pot, tye a wooden Spoon full of little Holes, to take the Pickles out with”.14
Glasse’s instructions reveal that colonists understood that proper storage and handling were essential components of food preservation. Although they did not understand microbial growth in modern scientific terms, their practices reflected an awareness that contamination and improper storage could reduce the shelf life of preserved foods.
Although fermentation was a known food transformation process in many parts of the world, there is limited historical evidence documenting intentional fermentation practices among Eastern Woodlands Indigenous communities prior to European contact. Valery Havard, in his article “Drink Plants of the North American Indians,” references missionary Gabriel Sagard’s observations of early Indigenous-European interactions, noting that Sagard described these communities as largely “saved from drunkenness.” Havard interpreted this observation as evidence that intoxicating alcoholic beverages were not a common feature of daily life among the Indigenous groups Sagard encountered.15 While some Indigenous communities in the American Southwest and Mexico produced fermented beverages, historical accounts suggest that these drinks were often associated with ceremonial and ritual practices rather than everyday consumption.16 The absence of extensive written documentation does not indicate a lack of knowledge regarding plant resources or food transformation. Eastern Woodlands communities had access to many naturally occurring sources of sugar, including maple sap, fruits, and berries, which can support fermentation under appropriate conditions. However, direct evidence of intentional fermentation practices remains limited. Instead, Indigenous preservation traditions more clearly documented during this period include methods such as drying and smoking, which are explored in the final section of this unit.
To produce the vinegar needed for pickling, colonists relied on a two-stage fermentation process. First, they produced alcoholic beverages, often from ingredients such as apples, corn, molasses, and honey. These alcohol-containing liquids could then be exposed to oxygen and naturally occurring acetic acid bacteria, which converted the alcohol into acetic acid, creating vinegar. According to the 1775 diary of John Page, colonists produced alcohol by converting “apples into ‘cyder’; corn into whiskey; imported molasses into rum; and honey into metheglin, a spiced mead of Welsh origin”.17
This process raises an important question: if bacteria are often associated with food spoilage, how can bacteria also contribute to food preservation? The answer lies in understanding how certain microorganisms produce acids that create highly acidic environments. These environments inhibit the growth and reproduction of many spoilage-causing microorganisms through a process known as bacteriostasis.
Bacteriostasis
The term bacteriostasis can be understood through its Greek roots. According to the Oxford English Dictionary, the word combines bacterio- (derived from the Greek bakterion, meaning “little staff” or “rod”) with -stasis (from the Greek stasis, meaning “standing still,” “stoppage,” or “inhibition”). Together, the term refers to the inhibition or slowing of bacterial growth rather than the destruction of bacteria. This distinction is important because many traditional food preservation methods, including vinegar pickling and fermentation, work by creating environmental conditions that slow or inhibit the growth of harmful microorganisms.
To understand how vinegar contributes to bacteriostasis, it is helpful to first examine the microbial processes involved in vinegar production. Yeast are microscopic, single-celled fungi that break down sugars found in fruits, grains, and other plant materials. Through a process called alcoholic fermentation, yeast convert these sugars into ethanol (alcohol) and carbon dioxide gas. The release of carbon dioxide produces the bubbles found in fermented beverages and is also responsible for causing bread dough to expand during baking.
When oxygen is present, a second group of microorganisms known as acetic acid bacteria convert the ethanol produced by yeast into acetic acid (CH₃COOH), the primary acid found in vinegar. As acetic acid accumulates, the pH of the environment decreases, creating increasingly acidic conditions. This low-pH environment inhibits the growth of many spoilage-causing and disease-causing bacteria, producing a bacteriostatic effect that helps preserve food while also creating the characteristic sour flavor associated with vinegar.18 Although colonists did not understand the role of microorganisms in vinegar production, their methods relied on naturally occurring microbial processes that modern science can now explain.
Since cucumbers are among the most commonly pickled vegetables, this discussion will focus on the chemical processes occurring within cucumber plant cells. Although the examples presented here involve cucumbers, the same fundamental principles apply to many other plant tissues. Cucumbers originated near the Himalayan foothills of India, yet they had spread far beyond their region of origin by the sixteenth century. French explorer Jacques Cartier documented observing cucumbers in Canada as early as 1535, demonstrating how widely the crop had traveled through trade and early European exploration.19 When cucumbers are submerged in a vinegar-based solution, acetic acid (CH₃COOH) moves into the plant tissue through diffusion. As the acidic solution interacts with the cucumber cells, the pH decreases, creating an environment that inhibits the growth of many bacteria, molds, and yeasts. Most foodborne pathogens are unable to grow effectively in environments with a pH below approximately 4.6, making acidification an important method of food preservation.20 Osmosis also occurs during the pickling process. Because the pickling solution contains a higher concentration of dissolved substances, including salt, sugar, and acids, than the fluid inside cucumber cells, water moves out of the cucumber through osmosis. At the same time, acetic acid, salt ions, sugars, and other flavor compounds move into the cucumber tissue through diffusion. As these substances enter the cucumber, they alter both its flavor and texture. The cell walls of cucumbers are composed largely of pectin, a structural polysaccharide that provides firmness and support. The acidic environment created by vinegar gradually weakens pectin structures, causing the crisp, firm cucumber to soften into the characteristic texture associated with pickles.21 Together, these processes of osmosis, diffusion, and acidification transform the cucumber’s texture and flavor while creating conditions that inhibit the growth of many spoilage microorganisms, ultimately extending the food’s shelf life.
Up in Smoke
I have saved one of the oldest forms of food preservation for the final section of this unit: smoking. Evidence of early human interaction with fire dates back hundreds of thousands of years. Researchers from Tel Aviv University examined archaeological evidence from fire-use sites in Israel, Africa, and Spain dating between approximately 800,000 and 1.8 million years ago. Based on the presence of large animal remains and evidence of controlled fire use, researchers proposed that early humans may have used fire not only for protection and processing food but also for smoking and drying meat to extend its shelf life.22 While these discoveries demonstrate early human use of fire for processing animal resources, evidence of intentional smoking as a preservation technique developed over time as communities learned to use smoke, heat, and airflow to extend the storage life of food.
Historical evidence demonstrates that smoking became an important preservation and cultural practice in many regions around the world. In China, evidence suggests that smoking practices date back to the Zhou dynasty, where smoked meat served both practical preservation purposes and ritual roles as offerings to ancestors.23 Similar preservation traditions developed among Indigenous communities across the globe, including communities in the Andes, the Amazon, Pacific Islands, and Australia. The widespread use of smoking demonstrates the adaptability and accessibility of this preservation method, as it required only two readily available resources: fire and wood. This was also true among many Indigenous communities in North America, where smoking and drying were important methods of preserving meat long before European colonists arrived. D.M. Kinsman, presenting at the 29th Annual Reciprocal Meat Conference of the American Meat Science Association in 1976, described the importance of Indigenous preservation knowledge to early settlers:
“The American Indians contributed much to the sustenance and survival of the earliest settlers through their friendly gestures of food,' shared hunting skills and meat preparation and preservation methods. One of these was that of drying meat on racks in the sun or over fires. of meats imparted both a drying and flavoring effect which was soon utilized for cured meats. A "meat house" was one of the first buildings erected by the colonists and it served both for smoking and storing smoked meats.”
Kinsman’s account illustrates how Indigenous preservation techniques influenced early colonial food practices, particularly the development of smokehouses for preserving and storing meats.24 By the eighteenth century, smokehouses had become common features on many colonial American farms. Tax records from Kent County, Delaware, indicate that by the mid-1700s, many farmsteads with additional structures included smokehouses used for meat preservation.25 These simple structures typically contained a fire source, ventilation openings, and designated areas for hanging or storing cured foods. Colonial smoking practices reflected a combination of European preservation traditions and Indigenous knowledge. In regions such as Virginia and the Carolinas, European settlers adapted Powhatan smoking techniques, including the use of hickory smoke, and combined them with European salt-curing practices. Over time, these adaptations contributed to regional traditions of smoked meats that incorporated ingredients such as molasses, brown sugar, and spices.26 While smoking is often associated with adding flavor, its historical purpose was primarily preservation through reducing moisture and exposing food to compounds within smoke that slow microbial growth. This combination of drying and smoke exposure explains why Indigenous communities and colonial settlers could preserve hunted meats for extended periods without refrigeration.
Pyrolysis
So, what is happening chemically when meat is smoked for preservation? The process begins with the production of smoke through a chemical reaction called pyrolysis. Derived from the Greek roots pyro, meaning “fire,” and lysis, meaning “separation” or “breaking apart,” pyrolysis occurs when wood is heated to approximately 300–700°C in an environment with limited oxygen. During this process, the major components of wood, hemicellulose, cellulose, and lignin, break down and release hundreds of chemical compounds that contribute to both the flavor and preservation effects of smoke.27 Hemicellulose decomposes first, producing compounds such as aldehydes, acids, furans, and lactones. Cellulose produces additional acids and aldehydes, which contribute to the characteristic flavors of smoked foods. Lignin produces many of the phenolic compounds responsible for the familiar smoky aroma and flavor. These phenolic compounds also contribute to preservation by slowing oxidation and inhibiting the growth of some microorganisms. The type of wood used during smoking influences the specific compounds produced, which is why different woods create distinct flavors.28
In addition to smoke compounds, heat exposure during smoking can contribute to browning through the Maillard reaction. This chemical reaction occurs when amino acids and reducing sugars react under heat, creating new flavor compounds and the brown color associated with cooked meats.29 Although many traditional smoked meats were first salted or cured, the smoking process itself provides additional layers of preservation. Similar to dry salting, smoking reduces the amount of available moisture within the meat, but it does so primarily through dehydration rather than osmotic movement. As meat is exposed to warm air and smoke, water gradually evaporates from the surface and interior tissues, creating an environment with reduced water availability. Because microorganisms require accessible water to grow and reproduce, this drying process slows the growth of many spoilage-causing bacteria.
After dehydration, smoke contributes chemical compounds that enhance both the flavor and preservation of smoked foods. During the pyrolysis of wood, compounds such as phenols, acids, and aldehydes are released into the smoke and deposited onto the surface of the meat. These compounds contribute to the characteristic aroma and flavor associated with smoked foods while also providing antimicrobial and antioxidant effects. Phenolic compounds are particularly important because they can slow the growth of some microorganisms and reduce oxidation, a chemical process that contributes to the development of rancid flavors in fats. Together, the reduction of moisture and the chemical effects of smoke create an environment that slows spoilage and allows smoked meats to remain edible for longer periods of time.30
The preservation methods explored throughout this unit demonstrate that while technology and equipment have changed over time, the scientific principles behind food preparation remain consistent. Kinsman also noted that many modern approaches to meat preparation and preservation are built upon the same fundamental practices used by early American communities, with changes occurring primarily in equipment, heat control, and technology rather than in the underlying processes themselves. Traditional methods such as salting, drying, and smoking relied on observations of how environmental changes affected food safety and quality. Today, food scientists can explain these same practices through concepts such as osmosis, dehydration, water activity, pH changes, and antimicrobial compounds. Understanding the chemistry behind these historical preservation methods allows students to recognize how scientific knowledge develops from human observation, experimentation, and adaptation over time.
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