Chemistry of Cooking

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Preservation of Food

Preservation of food has played an important role in many cultures around the world. This made it possible for people to travel great distances to explore unknown places. Taking their portable food provisions with them meant they would not starve. As people settled in new lands, they searched for ways to preserve life by preserving foods. What they found through observations and trial and error was a variety of ways to use the natural chemicals around them to develop different ways of preserving foods through different processes. Many cultures developed methods to preserve surpluses of foods within the climate that they lived in by utilizing smoking, and drying. In regions of the world where winter months meant starvation and the limited supply of fresh foods, people dried their food in the air, kept cool in caves, and cured meats by smoking them. Eventually, with the discovery of salt, they pickled and fermented fish, meats and vegetables.  As cultures harnessed the power of the sun’s heat and long winter months, salts, and eventually sugars and spices, vinegars and alcohols transformed the way cultures ate and influenced their culture and lifestyles.

Bacteria

The basic idea of preservation is handling and keeping food in such a way that the food maintains the quality of its texture, flavor, and color while avoiding spoilage and bacterial growth that can cause sickness and even death. Bacteria, one of the most common agents of food infection, are single-celled microorganisms that are too small to be seen with the human eye. Microbes live, die, and reproduce, and like all living creatures, they depend on certain conditions to survive and thrive.⁵ For growth to occur within food, microorganisms require the temperature between 40°F and 140°F, which is called the danger zone, for bacteria to grow rapidly. Time, more than two hours in the danger zone, can cause spoilage. Water, high moisture content is helpful. Fresh fruits and vegetables have the highest moisture content. Oxygen, most microorganisms need oxygen to grow and multiply, but a few are anaerobic and do not. Acidity and pH Level, foods that have a low level of acidity (or a high pH level) provide an ideal environment, since most microorganisms grow best around 7.0 pH and not many will grow below 4.0 pH. Examples of higher pH foods include meat, seafood, milk, and corn. Examples of low pH foods include citrus fruits, sauerkraut, tomatoes, and pineapples. Nutrient Content, microorganisms need protein, starch, sugars, fats, and other compounds to grow. Typically, high-protein foods are better for bacterial growth.⁶ As far as food is concerned, microorganisms can show themselves as harmless, harmful and beneficial. Microorganisms that thrive on moist, warm, aerated foods are often pathogenic, but not all microorganisms that live in and on food are lethal to us. Basically, everything we touch, breathe, or ingest contains some form of microorganism. On the other hand, some microorganisms will cause great harm when ingested. Examples are: Clostridium Botulinum, E. coli, Salmonella, and Norovirus.⁷ To prevent ingesting these harmful microorganisms, we need to be educated on the safety of hand washing, the identification of food pathogens that are associated with foodborne illness, food handling, and methods on how to preserve foods in a safe way for later consumption.

The Safety of Handwashing

Keeping hands clean is one of the most important steps we can take to avoid getting sick and spreading germs to others. Many diseases and conditions are spread by not washing hands with soap and clean, running water. Where can germs come from and how can we prevent them? Let’s define two important words that will be discussed in detail further on in this unit.

1. Microbes are all tiny living organisms that may or may not cause disease.
2. Germs, or pathogens, are types of microbes that can cause disease.

Did you know, germs like Salmonella, E. coli, and Norovirus, survive and grow in feces/(poop) from animals and even people? These kinds of germs can get onto hands after people use the toilet, but also in less obvious ways, like after handling raw meats that have invisible amounts of animal poop on them. A single gram of human feces which is about the weight of a paper clip can contain one trillion germs.⁸ Germs can also get onto hands if people touch any object that has germs on it because someone coughed or sneezed on it or was touched by some other contaminated object. When these germs get onto hands and are not washed off, they can be passed from person to person and make people sick.

Handwashing with soap removes germs from hands. This helps prevent infections because people frequently touch their eyes, nose, and mouth without even realizing it. Germs can get into the body through the eyes, nose and mouth and make us sick. Germs from unwashed hands can get into foods and drinks while people prepare or consume them. Germs can multiply in some types of foods or drinks, under certain conditions, and make people sick. Germs from unwashed hands can be transferred to other objects, like clothes, table tops, or utensils, and then transferred to another person’s hands. Removing germs through handwashing helps prevent diarrhea and respiratory infections and may even help prevent skin and eye infections.⁹

Handwashing is the most important thing you can do to prevent the spread of foodborne bacteria.

It may seem silly to think that you need to learn how to wash your hands. However, a proper hand washing method can make the difference between safe science room and a potentially deadly one. This is because harmful bacteria are so easy to spread by hand. The Center for Disease Control and Prevention (CDC), recommends cleaning hands in a specific way to avoid getting sick and spreading germs to others.

How to Wash Your Hands the Correct Way According to the CDC.

First, wet your hands with clean, running, warm or cold water, and apply soap. Using soap to wash hands is more effective than using water alone because the surfactants in soap, function by breaking down the interface between water, oils and dirt, and germs.¹⁰ Soaps were the earliest surfactants and are obtained from fats which are known as tri-glycerides because they are esters formed by the tri-hydric alcohol, propane-1,2,3-triol (glycerol), with long chain carboxylic acids (fatty acids). Second, lather your hands by rubbing them together with soap. Be sure to lather the backs of your hands, between your fingers, and under your nails. By lathering and scrubbing your hands you create friction, which helps lift dirt, grease, and microbes from skin. Microbes are present on all surfaces of your hand, and a high concentration of microbes under your nails. When washing, the whole hand should be scrubbed. Third, Scrub your hands for at least twenty seconds. By doing so, you are reducing the numbers of microbes on your hands, removing more germs from your hands than washing for shorter periods. Remember to sing the ABC song from beginning to the end, twice.  Next, rinse your hands well under clean, running water. Soap and friction help lift dirt, grease, and microbes, including disease causing germs from skin so they can then be rinsed off your hands. Rinsing the soap away with running water rather than standing water decreases your risk of recontamination. Last, dry your hands using a clean towel or air dry them. Germs can be transferred quickly to and from wet hands. So, your hands should be dried after washing.

The Safety of the Science Lab

Cleaning Before Food Preparation

To prepare for food preparation in the science lab, wash your hands for 20 seconds with soap and warm running water. Then clean and sanitize your food preparation workspace.  Make sure you wash, rinse, sanitize, and air dry all bowls, cutting boards, knives, pots, pans, and other utensils. Use only a knife dedicated to food preparation for that purpose. Try to avoid bare hand contact with food. Use disposable gloves. The garbage cans you use during preparation should be lined with a plastic bag and have a lid on it. Remember to store food, food containers, paper products, and utensils away from your food prep area. This is very important; be mindful of student allergies to certain ingredients (e.g. peanuts or wheat) when preparing food. Safety of the students comes first when cooking food with a heat source. Establish a clear “safety zone” around your table.

Disinfecting

The CDC recommends a disinfection solution made by adding 1 part sodium hypochlorite, NaClO / (common household bleach), to 9 parts of water. This solution will disinfect cutting boards, sinks, counters, knives, etc. The CDC also recommends an alternative to bleach, using soap and warm water.¹¹

Foodborne Pathogens

The U.S. Public Health Service has identified the following microorganisms as being the biggest culprits of foodborne illness, either because of the severity of the sickness or the number of cases of illness they cause.¹²

1. Campylobacteriosis is an infectious disease caused by bacteria of the genus Campylobacter. Most people who become ill with campylobacteriosis get diarrhea, cramping, abdominal pain, and fever within two to five days after exposure to the organism. The diarrhea may be bloody and can be accompanied by nausea and vomiting. The illness typically lasts about one week. Sources include: raw and undercooked poultry and other meat, raw milk and untreated water.
2. Botulism is a rare but serious illness caused by a toxin that attacks the body’s nerves and causes difficulty breathing, muscle paralysis, and even death. This toxin is made by Clostridium botulinum and sometimes Clostridium butyricum andClostridium baratiibacteria. These bacteria can be spread by food and sometimes by other means. The bacteria that make botulinum toxin are found naturally in many places, but it’s rare for them to make people sick. These bacteria make spores, which act like protective coatings. Spores help the bacteria survive in the environment, even in extreme conditions. The spores usually do not cause people to become sick, even when they’re eaten. But under certain conditions, these spores can grow and make one of the most lethal toxins known. The conditions in which the spores can grow and make toxin are: low to no oxygen (anaerobic) environment, low acid, low sugar, low salt, a certain temperature range, and a certain amount of water. Sources include: improperly home-canned, preserved, or fermented foods, and these can provide the right conditions for spores to grow and make botulinum toxin. Improperly prepared home-canned foods such as honey should not be fed to children less than 12 months old.
3. Escherichia coli(abbreviated as E. coli) are a large and diverse group of bacteria. Although most strains of E. coliare harmless, others can make you sick. Some kinds of E. coli can cause diarrhea, while others cause urinary tract infections, respiratory illness and pneumonia, and other illnesses. Still other kinds of E. coli are used as markers for water contamination. You might hear about E. coli being found in drinking water, which are not themselves harmful, but indicate the water is contaminated. Sources include: beef, especially undercooked or raw hamburger, produce, raw milk, and unpasteurized juices and ciders.
4. Norovirus is a very contagious virus that can infect anyone. You can get it from an infected person, contaminated food or water, or by touching contaminated surfaces. The virus causes your stomach or intestines or both to get inflamed. This leads you to have stomach pain, nausea, and diarrhea and vomiting. These symptoms can be serious for some people, especially young children and older adults. Sources include: any food contaminated by someone who is infected with this virus.
5. Salmonella is a bacterium that makes people sick. It was discovered by an American scientist named Dr. Daniel Elmer Salmon. It has been known to cause great illness for over 125 years. The illness people get from Salmonella infection is called salmonellosis. Most people infected with Salmonella develop diarrhea, fever, and abdominal cramps between 12 and 72 hours after infection. The illness usually lasts 4 to 7 days, and most individuals recover without treatment. The Salmonella infection may spread from the intestines to the bloodstream, and then to other body sites. In these cases, Salmonella can cause death unless the person is treated promptly with antibiotics. The elderly, infants, and those with impaired immune systems are more likely to have a severe case of the illness. Sources include: raw and undercooked eggs, undercooked poultry and meat, fresh fruits and vegetables, and unpasteurized dairy products.
6. Listeriosis is a serious infection caused by the germ Listeria monocytogenes. People usually become ill with listeriosis after eating contaminated food.The disease primarily affects pregnant women, newborns, older adults, and people with weakened immune systems. It’s rare for people in other groups to get sick with Listeriainfection. Listeriosis is usually a mild illness for pregnant women, but it causes severe disease in the fetus or newborn baby. Some people with Listeria infections, most commonly adults 65 years and older and people with weakened immune systems, develop severe infections of the bloodstream (causing sepsis) or brain (causing meningitis or encephalitis). Listeria infections can sometimes affect other parts of the body, including bones, joints, and sites in the chest and abdomen. Sources include: unpasteurized dairy products, including soft cheeses, sliced deli meats, smoked fish, hot dogs, paté, and deli-prepared salads including egg, ham, seafood, and chicken.

Methods of Food Preservations

Drying

Dehydrating (another word for drying) is one of the oldest methods of food preservation.  Early Egyptians dried fruits and vegetables, eventually, leading to dried fish and meats. With the power of the sun, early Egyptians knew that fresh fruits and vegetables contain a lot of water. When they set out fruits and vegetables into the extreme heat of the sun to dry they discovered that the heat from the sun, mixed with the air caused them to swell.¹³ After time, the fruits and vegetables had changed color, shape, and texture, but the taste from natural sugars intensified because of less water content. What happened was, when fruits and vegetables were placed in a hot environment (sun) heat transferred from the hot air to the flesh and water inside the food. Heat caused the energy of the water molecule to increase. When the energy of the water molecules reached a certain level, they changed from a liquid (water) to gas (water vapor). This changing phase is called evaporation. In fresh fruits and vegetables there lies a lot a water, about 90%. To be considered a properly dried fruit, it must only contain about 20%. Dried vegetables are even less, about 10%.¹⁴ This is important, because having very low water after drying, they become protected against microorganisms, like mold. Without water, microorganisms cannot grow and spoil fruits and vegetables. Why is this important? Eating dried fruits and vegetables can help keep us healthy and happy. Fresh fruit and vegetables are rich in vitamins, nutrients, and flavor which are retained when dried. Fruits picked at their prime have the highest natural sugar content and best nutritional value. For the best quality product, choose only fresh, ripe, unblemished fruits. Vegetables have a low acid and sugar content that makes them more subject to spoilage, and tend to have far shorter shelf life than dried fruits.

Dehydrator

The dehydrator with separated trays will be the essential tool in the science lab for drying; use one with a clear top so students can see the transformation.  Most dehydrators can be found online.

Cleaning

Fruits and vegetables will need a good cleaning to insure a safe product in the end. They should be placed in a colander, washed under running water, using a fruit/vegetable brush to scrub away any dirt. When cleaned, they are to remain in the colander to drain.

Fruit Preparation

Wash fruit thoroughly and remove any imperfections. Remove skins (if desired), stems, and stones. Cut the fruit in half or slice in 1/4" to 1/2" circles or slices. Some fruits have a natural protective wax coating such as figs, prunes, grapes, blueberries, cranberries, etc. If you want to dry these fruits whole, dip into boiling water for 1 to 2 minutes (amount of time needed depends on thickness and toughness of skin) to speed dehydration. This makes the skin more porous by removing the natural wax coating and speeds up drying time. Small lines appear on fruit skin allowing moisture to escape but may be too fine to be visible. Many fruits can be dried in halves with the pits removed. If drying with skins on, make sure to dry skin side down to prevent juice and pulp from dripping down through trays. If fruit has been artificially waxed, it should be peeled to remove wax. Pre-treatment isn't necessary for most fruit. Fruits are simply sliced and dried. However, some fruits tend to oxidize more than others. Oxidation causes browning of cut food surfaces when fruit is dried. This causes a loss in flavor and vitamins A and C. Pre-treatment minimizes oxidation. Apples, pears, peaches and apricots are better when pre-treated before drying. To pretreat, place cut fruit in a holding solution of ascorbic acid, C₆H₈O₆, (vitamin C) to reduce browning during preparation. Do not keep cut fruit in a holding solution for more than an hour.

Vegetable Preparation

Wash vegetables thoroughly and remove any blemishes. Peel, trim, core, and/or slice vegetables. Most vegetables must be blanched, either steaming over boiling water or in microwave oven to slow enzyme action which will continue during drying and storage. Blanching softens cell structure, allowing moisture to escape more easily and allows vegetables to dehydrate faster. Using a pot with a tight-fitting lid and a steaming rack, bring about 1 inch of water to a brisk boil and drop in sliced vegetables. Cover and steam until vegetables are heated completely through, but not cooked. This is usually about 1/3 of the time required to cook vegetables. Vegetables should still be crunchy. Drain in a steamer rack and place immediately on dryer trays.

Vegetables are dried until they are crisp, tough, or brittle. Package into airtight containers immediately after drying to prevent absorption of moisture from air. The usual drying temperature for vegetables is 130°F to 145°F.

Fermentation and Pickling

Fermentation is one of the oldest and simplest means of preserving food.¹⁵ There is no need to cook, no heat is wasted, all that is needed are a holding vessel, salt, and a weight to hold the food in its natural juices. Fermentation occurs when certain harmless microbes, with limited presence of air, will grow and inhibit the growth of other unwanted microbes that may cause spoilage and disease. Organisms known as yeast consume sugars and convert them to alcohol, carbon dioxide, and lactic acid over the course of several weeks.¹⁶ Pickling on the other hand, is preserving foods in acetic acid, CH₃COOH / (vinegar), or other acids. Vinegar is produced from starches or sugars fermented into alcohol and the alcohol is oxidized to lactic acid, C₃H₆O₃ / (milk acid).¹⁷

Sauerkraut

Sauerkraut involves anaerobic bacteria, which is why the shredded cabbage and salt need to be packed in a  water lock container. At this stage, the surrounding environment is not acidic, just cabbage. The bacteria, mostly Leuconostoc species, produce carbon dioxide (replacing the oxygen in the jar) and lactic acid, which is a natural byproduct of anaerobic respiration. Eventually, the conditions within the jar become too acidic for these bacteria to survive and they die out, replaced with bacteria that can better handle the acidic conditions such as Lactobacillus species. The lactobacillus further ferment any sugars remaining in the cabbage, using anaerobic respiration. This produces more lactic acid, until the sauerkraut reaches a pH of about 3. These bacteria are inhibited by high salt concentrations (so most sauerkraut contains around 2-3% salt) and low temperatures, which is why the fermenting jars should be left at room temperature rather than in the fridge. At pH 3 the lactobacillus stop fermenting and the sauerkraut can be stored until needed.¹⁸

Science Sauerkraut in a Fermentation Crock

A fermentation crock (glass and plastic) is highly recommended for a visual examination of the process of the transformation, as it has a built-in water lock to create an anaerobic fermenting environment. Glass fermentation crocks are available on-line.

Preparation

You will need about 2-3 large heads (6-8 pounds) of green cabbage. Cabbage will be cut into quarters and sliced about 1/8 inch thin. Stuff shredded cabbage in the fermentation crock pressed down firmly and add 6 tablespoons of canning/pickling salt. Other types of salts may have anti-caking ingredients in them. This may make the brine cloudy but, harmless. Make sure to leave about ¾ of an inch of headspace between the cabbage and the rim of the crock. Add the weight on top to suppress the cabbage and place water in the rim of the crock and place lid on top. Place the crock in an area of the science lab where it can be seen. If, after 24 hours, the brine does not cover all the cabbage, add some filtered water and a pinch of salt. Once the desired pH 3 level has been reached, transfer to airtight jars with lids and refrigerate until ready to serve.¹⁹

Testing pH Levels in Sauerkraut

Paper pH testing strips, also known as litmus paper, change color when put into the substance being tested. The resulting color indicates the pH of the substance, correlating to the manufacturer’s label. When you use the pH strips to test the pH of sauerkraut, it is necessary to take a teaspoon of the sauerkraut, and the sauerkraut juice and puree them together for testing. You can’t simply put a test strip into the sauerkraut without blending first. It will not give you an accurate pH reading.

Sugar Preservation

Like salt, sugar makes the fruit inhospitable to microbes. It dissolves, binds up water molecules, and draws moisture out of living cells, thus crippling them.²⁰ The key to creating fruit preserves is pectin.²¹ Pectin keeps things together, it's a naturally occurring carbohydrate with thickening and gelling properties. When fruit is cut up and heated to near boil, the pectin chains are shaken loose from the cell walls and dissolve into the released cell fluids and any added water.

Recipe for Strawberry Preserves

You will need 4 cups of mashed ripe strawberries, 4 cups of granulated sugar, and 1 tablespoon of citric acid. Wash fruit thoroughly and remove any imperfections. First, mix sugar and berries in a bowl and let sit at room temperature for about 1 hour. After 1 hour, transfer to a pot and add the citric acid and bring to a full rolling boil for 7 minutes, stirring constantly. Then, pour into 8 pre-sterilized half-pint jars, leaving ¼” headspace. Process in a boiling-water bath for 10 minutes. The preserves may be kept for one year in a cool, dark area.

Preservation Tools of the Trade

Utensils for Canning

The following canning-specific tools may be purchased on-line: Jar lifter, magnetic wand, jar funnel, and a combination ruler/spatula. These also can be purchased on-line: Induction cooktop with induction cookware, measuring spoons, ladles, ruler, measuring cups, kitchen towels, timer, pot holders, colander, large sieve, 4 and 8 cup glass liquid measures.

Boiling-water canning

For the purpose, of this unit, I recommend The Ball^® freshTECH Electric Water-Bath Canning System. This tabletop water canner is perfect for the science lab. A boiling-water canner is simply a very large pot with a rack on the bottom and a lid on the top. Jars are submerged in simmering water for a specified time. They then are heated to a temperature of 212⁰F; this method is used mainly for fruits, pickles, salsa, and other high-acid foods.²²

The Anatomy of a Canning Jar

Addi. “Anatomy of a Canning Jar.” ²³