Content Objectives
Doing What Scientists Do
The National Science Teaching Association (NSTA) was formed in 1944 and is currently the largest professional organization that focuses on the teaching of science in the world. The group was a guiding force in developing the Next Generation Science Standards (NGSS). In November of 2025, the NSTA released a list of best practices related to science education. The biggest shift in strategy is a departure from primarily lecturing to deliver content. In its place is a focus on engaging students in science and engineering practices. This is a shift from passively receiving content to actively engaging in discovery. The NGSS are a reflection of this new approach to the teaching of the sciences. The state of Delaware public school system follows the NGSS when planning the teaching of science content. The NGSS is divided into 4 separate domains: physical sciences, life sciences, earth and space sciences, and engineering, technology, and the applications of science. This last domain is a large part of science education in the primary grades. “This domain involves the application of scientific knowledge to design solutions using engineering and technology. Within this domain are skills such as defining problems, designing and testing solutions, and critical thinking.”[1] To put it simply, the NGSS mandate that students do what scientists do, in a grade and age level appropriate manner. I plan to engage my students in several science and engineering practices including making observations, and predicting, measuring, and communicating their ideas and findings.
Physical Changes, Chemical Changes, and Mixtures
Physical and chemical changes can be difficult to determine at times. However, both types of change do have distinct definitions. Physical changes change the form of the substance, but not its molecular structure. For example, an ice cube melting into water is a physical change. Both ice and water have the same molecular formula: two hydrogen atoms and one atom of oxygen. Thus, water and ice are the same substance but in different phases of matter. Another example of a chemical change is when someone breaks a first aid kit cold pack. Many of these packs contain ammonium nitrate, sealed in a plastic bag, and water surrounding that sealed bag. When the cold pack is popped, the ammonium nitrate is dissolved in the water and an endothermic reaction ensues. An endothermic reaction absorbs heat from the surrounding making those surroundings cooler.[2] Physical changes could include the changing of a substance’s texture (like sanding a piece of wood), shape (possibly but cutting or stretching something), temperature (like heating metal until it glows). These types of changes do not permanently alter the substance’s composition.
A chemical change is when the molecular composition of a substance is changed through breaking and forming of chemical bonds during a chemical reaction. Often the presence of certain indicators reveal that a chemical change has occurred. Examples of this indicator would include: a change in temperature, a change in color, the development of an odor, or the formation of either a precipitate (a solid substance formed by a chemical reaction) or a gas. An example of chemical change would be burning wood which releases heat and results in a transformation of wood into carbon dioxide, water vapor, and ash.[3] Chemical changes cannot easily be reversed or undone.
Mixtures are formed when multiple substances are combined together. The mixing of substances does not break or form bonds and the substances do not undergo a chemical change. A mixture can be sorted back into its disparate parts through many techniques. Some examples of these techniques would be using a magnet to remove iron filings from non-magnetic compounds, the filtration of pollutants from water, and the distillation of salt water.
Graham Crackers
Named after the clergyman and health reformer, Sylvester Graham, the Graham Cracker was invented in 1829. At the time, its ingredients included unsifted, coarsely ground whole wheat flour which was baked without fat or refined sugar. The modern-day Graham Cracker would likely be unrecognizable (and horrifying) to the health-minded Sylvester.[4] Today’s commercially sold Graham Crackers commonly are made with whole-wheat flour and enriched white flour, treated with niacin, reduced iron, vitamins B1 and B2, and folic acid. Included sweeteners could be sugar, molasses, corn syrup, or some combination of the three. Soybean, canola, or palm oils and often honey are added to provide fats and flavoring. Baking soda, sodium acid pyrophosphate, monocalcium phosphate and soy lecithin are additives and leavening agents. Students will likely associate Graham Crackers with s’mores, traditionally a combination of the crackers with chocolate and toasted marshmallow. As with most crackers, the Graham Cracker is brittle and is very easy to crumble into tiny bits. The crumbles can then be combined with butter and other ingredients to make a pie crust, or as a topping to sprinkle over deserts like ice cream which we will be using it for in class. Transforming a rectangular Graham Cracker into crumbles is a physical change, and an easy example for students to wrap their head around.
Marshmallows
Marshmallows are over 4,000 years old. Initially they were used for the medicinal purposes or treating a cough, aiding digestion, and soothing irritated skin. A syrup was derived from the roots of Althaea officinalis, commonly known Marsh Mallow, as it was found in marshy locales. In the 1800’s, marshmallow lozenges (as they were then called) became gelatin based which eliminated the need for the plant’s roots. Marshmallows gained popularity in the 1920’s when a Girl Scout publication promoted placing them in hot cocoa. What started as a medicine has changed over the years. What begin with a marsh plant is now a popular snack unconnected with its original purpose or recipe.[5]
A typical marshmallow is made of sugar, corn syrup, gelatin, and air. “The marshmallow is basically a foam that is stabilized by gelatin.”[6] Gelatin is made by breaking down collagen which molecularly is a triple helix. When gelatin is added to warm water the heat causes the protein strands to spread out in the water. As cooling happens, the helices (helix plural) bunch back up becoming firmer, but some strands do not, and these retain their flexibility. This blend of firm and stretchy gives gelatin and thus marshmallows their texture.[7] When a marshmallow is roasted, the outer layer becomes crunchy and it turns brown (or black and flaming if you aren’t careful or prefer that). While the exterior is tanning, the interior becomes very soft almost to the point of being a viscous liquid. This transformation of the exterior is due to the properties of gelatin and a result of the Maillard Reaction. The Maillard Reaction causes browning in bread, steak, cookies, marshmallows, and many other foods. For this reaction to take place, both proteins (in gelatin) and sugar (an ingredient of marshmallows) must be available in the food being cooked. The first step of the reaction sees amino acids (found in protein) and sugar react and create a compound. These molecules form an aromatic ring which helps determine the speed of the reaction. In the final step, large complex molecules, melanoidins are formed. Melanoidins drive flavor and aroma during the cooking process and eventually give the food a brown color.[8] All of that basically means that the browning of a marshmallow during roasting is a chemical reaction involving the proteins and sugars found in a marshmallow. One interesting thing is that while the outer layer of the marshmallow is undergoing a chemical change thanks to the Maillard Reaction, the interior of the marshmallow is undergoing a physical change as the heat makes it gooey. The interior will firm up if the roasted marshmallow has the opportunity to cool.
Ice Cream
The first recipe for ice cream dates back to 1682. This early recipe called for powdered sugar and minced orange petals to be mixed in sweet cream. This mixture was to be poured in a pot. The pot was to be placed in a wine cooler and then crushed ice and salt were layered around the vessel. Over an anticipated two hours of time, the pot was to be shaken periodically to keep it from freezing solid. Frozen cream (without additional ingredients) will freeze and become as hard as rock. The addition of sugar makes the mixture softer but it comes with a lowering of the freezing point. This is problematic because, when the freezing point of the cream mixture is lower than that of water, the ice used to help freeze the concoction melts into a slush prior to freezing the cream. The salts dissolve in the slush lowering its freezing point enough that the cream mixture can be frozen and change into ice cream.[9] As early as the 13th century, the Arab world understood the effects of salts on freezing. The genius notion of the application of this knowledge of salting the ice led to the process of making ice cream. Through the late 1600s, the French improved upon the original process and recipe by incorporating a greater amount of stirring which made for a less crystalline texture. They also developed a far richer version by incorporating 20 egg yolks per pint of cream, which they called ice butter. Additionally, the French began flavoring the mixture with a variety of nuts, spices, orange blossoms, caramel, chocolate, tea, coffee, and rye bread. Another great innovation came from America in 1843 when Nancy Johnson of Philadelphia patented a freezer consisting of a large bucket for brine and a sealed cylinder for the cream mixture which had a handle and blade that allowed for continuous stirring. About a decade later a milk dealer by the name of Jacob Fussell began selling his surplus milk for the purpose of making ice cream. He sold the supply at a discounted rate. This led to large-scale manufacturing of the treat making it more accessible to masses of people.[10]
To better understand ice cream, we need to explore the chemistry involved in its creation. We can start with a look at the individual ingredients that go into the cream mixture and the substances that are foundational to the process of its making.
Milk (Fat)
There is a reason that the product we are working with is called ‘ice cream’ and that is because cream cannot be made without milk. The only difference between milk and cream is the percentage of milk fat in the liquid. The cream is the higher-fat layer that is skimmed from the milk. There are many types of cream used in a variety of cooking. With an eye toward ice cream, clotted cream has the highest milk fat percentage of at least 55%. Heavy whipping cream (which will be used in the lessons) has a milk fat percentage of no less than 36%. Half and half, which is the cream most usually put into coffee, only has a milk fat of 10-16%. Whole milk on the other hand only has 3.5% milk fat.[11] Milk fat is important to ice cream in four ways; first, during the churning fat globules trap air within the mixture (more on air later). Second, milk fat makes the mixture thicker which slows the melting time of ice cream. Third, simply put fat delivers flavor. Lastly, fat brings the creamy texture that is associated with the frozen treat.[12] Without enough fat, the overall structure of the mixture suffers due to a lack of air. Also, ice cream with insufficient fat tends to be harder to scoop and it is icier. However, a higher fat content is not always desirable. People that are counting calories may shy away from ice cream with a higher fat content. Creams with a higher fat content can be more expensive than a cream with a more modest percentage. Besides the fat, there are other components of milk that serve a purpose too. Milk also includes proteins, lactose (milk sugar), and other minerals. These components of milk help build an ice cream’s body and texture. The proteins act as natural emulsifiers which help bond the water molecules to fat molecules within the mix, and help reduce the formation of large ice crystals which would give the mixture a grainy texture.[13]
Vanilla (Flavor)
Vanilla is a wildly popular flavor that is used world-wide. The use of vanilla dates back to the Aztecs who used it to flavor their drink ‘xocolatl’, which features cocoa and vanilla beans harvested from the vanilla orchid.[14] Since demand for the flavoring is so overwhelming, the natural supply cannot meet the demand and vanilla beans are rather expensive. Scientists isolated the molecule that gives vanilla its distinct flavor. That molecule is vanillin, an organic compound which has a chemical formula of C8H8O3. Science has also allowed us to synthetically produce the vanillin molecule. There are two main ways to approximate the flavor of vanilla. The first is to “transform a similar molecule into vanillin: for this method, manufacturers look for components readily available, that contain a molecule that’s very similar to vanillin. They then isolate the molecule and transform it into vanillin.”[15] The other strategy is to “Use a microorganism to make it: ever since scientists found a way to use microorganisms to make insulin (essential for people with diabetes), developments have continued to happen. Manufacturers nowadays use microorganisms to make”[16] the ingredient vanillin. What to call synthetic vanilla extract varies dependent upon local laws, but most vanillin produced through molecular transformation end up being labeled as ‘artificial vanilla extract’. The vanillin produced through the use of microorganisms is usually harder to define.[17] Whether the flavor comes from the vanilla orchid or the laboratory, one thing is certain, vanilla is by far the most popular variety of ice cream worldwide.
Sugar (Sweetener)
“One taste sensation is undeniably the favorite of our species and of many others in the animal kingdom from hummingbirds to horses: sweetness.”[18] The most used sweetener used in ice cream is sucrose also known as table sugar. However, it is not uncommon to blend sugars together to tinker with the properties of the ice cream. Corn syrup, dextrose, glucose, and liquid glucose are common substitutes of or additions to sucrose. The obvious role that sugars play in ice cream is that they add sweetness to the product. Satisfying our sweet tooth is not the only role that sugar plays in the production of ice cream. Sugars also lower the freezing point of the mixture. They control the temperature-hardness relationship which determines how firm or soft the ice cream will be at any given temperature. Without sugar the mixture would likely freeze rock solid. The level of firmness or softness helps determine the ‘scoopability’ of the product when it’s taken from the freezer.[19] Additionally, sweeteners increase the total amount of solids in the mixture. Solids in the mix effect the body, texture, and smoothness of the product. “More solids means less ‘free-roaming’ water in the ice cream – which in turn usually means less unwanted, large ice crystals in the ice cream.”[20] “Ice crystals range in size from about 1 to over 150 micrometers in diameter, with an average size of about 25 micrometers. Small ice crystals, around 10 to 20 micrometers in size, give ice cream its smooth and creamy texture, whereas larger ice crystals, greater than 50 micrometers, impart a grainy texture.”[21]
Air
During the churning process, air is folded into the ice cream mixture. Also during the process, the fat globules or micelles, from the milk, come together and form a network which traps and stabilizes air bubbles. The amount of air captured during churning is measured as ‘overrun’. ‘Overrun’ is the measure of the percentage increase in the volume over the pre-churned ingredients. So, if an ‘overrun’ measure is 100%, that means half the volume of the ice cream is the captured air. More expensive ice creams may have a lower ‘overrun’ and that results in a richer and creamier mouthful. Conversely, less costly ice cream may exceed 100% ‘overrun’ and thus would have less ingredients and more air than an equal volume of ice cream with a lower ‘overrun’. The amount of air incorporated into the mixture can also greatly affect the texture of the ice cream. Air’s most important role in ice cream is that it keeps the mixture from freezing solid and promotes a softness to the finished product.
Ice & Salt
While not ingredients in the ice cream itself, ice and salt (NaCl) have played a critical role in the process of producing the frozen treat since its earliest incarnations. Melting ice has the useful property of making things cold. “It takes energy to break the bonds that hold water molecules together in ice. If you put an ice cube into room-temperature water, the energy in the fast-moving molecules in the water will get used up making chemical bonds as molecules freeze onto it, but the molecules leaving the ice will not have a lot of energy and will be moving slower, and they will be colder.”[22] Cooling will continue until an equilibrium temperature is reached at which point cooling ceases. In pure water, this equilibrium point is reached at 32 degrees Celsius or 0 degrees Fahrenheit. However, the addition of either salt to the water (or slush or melting ice) will allow the cooling process to go below the freezing point of pure water. If salt is further added, the equilibrium temperature will bottom out at -21 degrees Celsius or -6 degrees Fahrenheit, which is the point when the water can absorb no more salt. Interestingly, sugar would also work to allow the cooling process to go below the freezing point but sugar is more expensive than salt, so salt is the preferred substance. This is why ice and salt have long been used in the process of making ice cream.
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