Beyond the Dairy Aisle

Whether it’s with your cereal first thing in the morning, or in a glass with some chocolate syrup at night, milk is a staple part of most people’s diets. If it’s anything like mine, your family probably goes through at least a few gallons of milk every week, if not more. Milk comes in all different forms, too: without milk, you wouldn’t be able to put that whipped cream on your apple pie, or butter your toast during breakfast. Although it seems pretty simple, the physical status of milk is actually extremely complex, especially when it comes to the chemistry behind it.

The Chemistry Behind Milk

If you were to leave a glass of milk to sit for some time on your countertop, you would begin to see a thin layer of cream form on the surface of the milk. What exactly is this? Well, if you were to view this layer under a microscope, you would see shapes floating around in the milk, which is the fat. In chemistry, this is known as an emulsion; specifically, an emulsion of fat in water. An emulsion is a mixture of two or more liquids that are non-mixable. If you were to shake the glass of milk, the emulsion would be broken down and the milk would go back to normal. However, milk does come in more than one form, such as butter – the difference is that butter is an emulsion of water in fat. So when the milk is churned into butter, there is a phase change that is involved in the process.

The fats that are present in milk are there for a reason- they act as a solvent for all of the fat-soluble vitamins in milk that make it so healthy, such as Vitamins A, D, E, and K. In the milk fats, the fatty acid molecules are made up of a hydrocarbon chain along with a carboxyl group, or COOH group, usually, consisting of all single bonds, one double bond, and an even number of carbon atoms. Structurally, these chemical molecules look something like this:


Other properties of milk, such as the melting point and the hardness of the fatty acid, is affected by various factors such as the length of the previously mentioned carbon chain as well as the degree of unsaturation (when a molecule is unsaturated, this means that it does not have the greatest possible amount of hydrogen atoms that it can have for the number of carbon atoms that it has. In other words, fats with a lot of these high-melting fatty acids will be hard; but fats with a high content of low-melting fatty acids can make the spreadable butter that you put on your toast every morning.

Making Your Milk Taste Its Best

Depending on what kind of environment your store your milk in, you may notice that the milk tastes different. Changes in storage can cause different types of chemical changes to occur in the milk, one of them being oxidation. Although most people tend to think that milk changes or goes bad when it is left outside of a refrigerator because of the higher temperatures, there are actually a lot of chemical processes occurring in milk when it is exposed to lower temperatures as well, such as the oxidation of the fats in the milk.

Although the oxidation of the fats in the milk can be counteracted by reducing agents that are present in the milk, such as lactic acid bacteria, there are still many chemical changes that may cause some unwanted things to occur in your milk. For example, chemical change that occurs due to the oxidation of the fats in the milk is the “flavor” of the milk – although plain milk does not actually have a flavor to it, lower storage temperatures usually cause milk to develop an unpleasant flavor. This is why companies that produce milk place great emphasis on precise refrigeration for their milk, because nobody wants their milk tasting funky!

Got Milk?

Among the many beverages that have come to prominence in society throughout history, milk, along with water, is probably among those that will continue to be a mainstay in the diets of people both young and old. The small cardboard milk carton you get at lunch, the glass full of milk that you dip your Oreo in, the milk mustache you get on your upper lip when you take a sip. All of these are iconic images that come to mind when one thinks about milk throughout history. After taking away this information regarding the chemistry behind milk, one could also realize that not only will milk remain a staying force forever, but so will its chemistry.

Beavers and Vanilla

Why flavorings smell and taste the way they do

By Mark Sabini, Justin Yu, and James Lee

Imagine a cave of darkness lined with white pearly stalactites and stalagmites. On the ground is an organic carpet of living red, and there is an uncomfortable dampness in the air. Liquid flows all over the ground, making navigation difficult. Now imagine moving to another location with two doorways, side by side, carrying breezes of air in and out. They both look the same, mirror images of each other. Peering inside, you see what seems to be a grass of some sort, except that it grows all around the surface of the doorway, not just on the ground. You step inside, into a tunnel of blackness, and then whoosh! A strong breeze sucks you in, into oblivion. Now reflect on where you have just been: a human mouth and a human nose. Working together, these organs make up 40% of the five senses, and give flavor to food and aroma to flowers. How exactly do these marvels of nature function?

Taste and Smell

Taste relies on the transformation of chemicals from food (tastants) into nerve signals. The tongue’s mucous membrane is lined with tiny bumps called taste papillae. These little sensors responsible for taste perception consist of taste buds with sensory cells. The sensory cells form a little “cup” (see picture), which contains taste hairs. The proteins on the surface of the taste bud bind the chemicals from the food to the sensory cells for tasting. Then, the sensory cells transform the chemical signals into electrical signals that travel along nerves to the brain. Contrary to popular beliefall parts of the tongue are equally sensitive to the five tastes, sweetness, sourness, umami, bitterness, and saltiness, except the back of the tongue. The cells there are more sensitive to bitterness, most likely as a natural defense against swallowing bitter plants containing poisons.

Figure 1: Diagram of a typical taste bud
Figure 2: Video about taste

Smell works slightly differently from taste, but still employs the same basic principle: the transformation of chemical signals to electrical signals. At the top of every person’s nasal passage is a patch of neurons that is exposed to air. The neurons have small hairlike projections called cilia, to which volatile food chemicals (odorants) bind and cause transmission of electrical signals along the neurons to the olfactory bulbs on the underside of the frontal lobe. As a result of this mechanism, only volatile compounds will have smells. While they might seem unrelated, taste and smell work hand in hand. The data from the two senses is merged in the insula, a part of the brain, to put together what we know as flavor. This is why you cannot sense flavor when your nose is blocked – the smell component of flavor is missing.

Figure 3: Diagram of the Olfactory System. The patch of neurons located at the top of the nose feed into the olfactory bulb which sends signals directly to the brain.

The Chemistry of Flavorings

Esters are a class of organic compounds that have distinctive tastes and smells, and are used widely in the food industry.The ester octyl acetate, for example, is responsible for the characteristic citrus smell and taste of oranges. Esters can be prepared through Fischer-Speier esterification, in which a carboxylic acid and alcohol are reacted in the presence of an acid catalyst. The strong smell of esters is attributed to their volatility and the functional groups attached to the ester group. A list of commonly-used esters and their tastes and smells is shown below.

Figure 4: Fischer Esterification Figure 5: Chemical structures of some common esters

Other flavoring ingredients come from more natural sources, albeit quite strange ones. One example is castoreum, a brown, slimy secretion from the castor sacs located near a beaver’s anal glands. It has a vanilla taste after some processing, as it is originally mixed in with beaver urine and other impurities from the animal. Castoreum contains chemicals such as phenols and ketones, all contributory towards the smell and taste. According to MSU flavor chemist Susie Bautista, castoreum is not used much (since it is not kosher), but greatly enhances vanilla flavor. A similar chemical to castoreum is vanillin, a phenolic aldehyde. Vanillin is a component in both natural and artificial vanilla flavoring. Occurring in natural vanilla pods, vanillin can be extracted from the natural source. Otherwise, it can be synthesized from a chemical called guaiacol and glyoxylic acid. Chemical synthesis accounts for the vast majority of vanillin production in the world.

Figure 6: Left: Castor sacs from a beaver and castoreum. Right: Vanilla Pod
Figure 7:Vanillin and4-Ethylphenol1,2-dihydroxybenzene, and 3-hydroxyacetophenone: three components of castoreum; there are clear similarities between the chemical structures which accounts for their similarity in taste/odor

Figure 8: Chemical synthesis of vanillin from guaiacol

Another chemical that has gained much publicity is monosodium glutamate, MSG for short. MSG contains around 80% glutamic acid and contributes to the taste ‘umami,’ which is a taste found in cured meats, mushrooms, and cheeses. MSG is used as a flavor enhancer to greatly improve the flavor of many foods. It does so by providing glutamic acid to bind to the glutamate receptors on the tongue, allowing food to taste “meatier”, and therefore tastier. However, its wondrous properties do not come without negative effects. MSG can lead to eye damage, depression, and a whole host of other problems, as well as cause “Chinese Restaurant Syndrome,” which affects MSG over consumers with headache and asthma. This chemical is one example of why are chemical food flavorings require careful scrutiny. The benefits of taste may be outweighed by the health related downsides.

Figure 9: Structure of glutamic acid, a major component of MSG.


Smells and tastes are caused only by the chemical binding of compounds to receptors in the tongue and nose. In order to be smelled, a chemical must be volatile, or no odor components will enter the nose. Many chemicals play important roles in tastes and smell. For example, esters are a class of organic compounds with strong smells commonly found in fruits such as bananas and apples. Other flavor compounds include vanillin and castoreum, which are both used as vanilla flavorings. While both compounds emulate the same flavor, vanillin, a phenolic aldehyde, is found naturally in vanilla pods, while castoreum, a mixture of phenol and ketones, is produced in beaver castor glands. These compounds easily highlight the ability to “fool” the taste buds. Finally, monosodium glutamate, MSG, is a chemical responsible for the umami taste in foods. Its numerous adverse effects show the potential dangers of using flavorings and the need for in-depth analysis of the effects of flavor compounds on humans. The complexity of flavors highlights the need for humans to scrutinize the additives in their food. Who knows – the next vanilla iced coffee you drink might not actually have vanilla.

Beat the Heat: Investigating Garlic Powder

The ingredients list as seen on a typical bag of Flamin’ Hot Cheetos.

Snacking is a quintessential pastime in American culture. At many times, we have seen ourselves mindlessly reaching for the nearest box of Cheez-Its simply because, well, we need something to reduce our cravings before our next main meal. And the snack companies are aware of our almost subconscious cravings such that the potato chip company, Lay’s has its slogan as “Betcha can’t eat just one,” essentially taunting the hunger-stricken American public in the process. Personally, a favorite snack of mine is a nice bag of Flamin’ Hot Cheetos. This modern delicacy is extremely addicting, and as its name implies, is intensely spicy, so much that your nose might drip a bit as you inhale the strong spices in the bag. Curious to why this snack caused this reaction in me, I decided to ask the heads at Frito-Lay themselves about their product. What ingredients in the Cheetos make this notorious spicy flavor? I wrote to them:

I was eating Flamin’ Hot Cheetos the other day, and I took a look at the ingredients list because I was curious at what spices made the Cheetos so hot. I specifically noted the onion powder, garlic powder, and natural flavor. Is the spiciness of your product because of these three ingredients or are there others on the list to enhance the spicy flavor? Also, I was wondering what is ”natural flavor” and what is it made up of? Thanks so much, hope to hear from you soon! 

Frito-Lay replied with the following:

Thank you for writing to us. 

The “heat” in Cheetos Crunchy Flamin’ Hot is a secret–and that’s why it’s included under “natural flavors.” Using terms like “spices” and “natural flavors” on ingredient statements, is the way food companies protect their proprietary recipes. 

You’re right about the other seasonings like garlic and onion (two ingredients that must always be listed when used). They are included in the seasoning to enhance the flavor.

We consider you a valued consumer and hope you will continue to enjoy snacks from Frito-Lay. 

Best regards,


Frito-Lay Consumer Relations

It was understandable for Linda to not disclose what exactly is “natural flavor,” but nevertheless, I could deduce that the garlic and onion powder contribute to the Cheetos’ distinct flavor. And with this information, let’s look into the contents of specifically, garlic powder.

The Chemistry of Garlic Powder

Biologically active (or “bioactive”) components are the biomolecules that are responsible for influencing the various metabolic processes in foods. It is because of these bioactive food components that foods display their health benefits. For example, bioactive compounds such as dietary fiber found in many fruits and vegetables such as apples, broccoli, and carrots allow for capturing of harmful toxins in the digestive tract. Once completing its function in the digestive tract, this all-important bioactive food component consequently prevents constipation in the body and possibly even lowering one’s risk of heart disease or diabetes. Garlic powder is an interesting ingredient in that it does not actually contain the major biologically active component of garlic, allicin. In fact, fresh garlic in general does not directly contain allicin either! This apparent commodity can all be explained once the intricate chemistry of garlic is investigated.

A visual representation of the chemical reaction that forms allicin from alliin.

Within a sample of fresh garlic is a chemical known as alliin, which is its natural constituent. In addition, the enzyme, alliinase, is also found in fresh garlic. Like most enzymes, alliinase acts as a catalyst in a chemical reaction. Because the alliinase molecule acts as the catalyst, it would consequently lower the activation energy of the reaction to speed up the process. In this case, it would speed up the creation of allicin.

However, alliinase acts in perhaps the most important chemical reaction regarding fresh garlic. As we all know, garlic is noted for its strong smell and flavor, but most notably, its ability to generate tears when cut. Chemicals that give garlic these distinct qualities are supplied via this reaction between alliin and alliinase. Alliinase is released and subsequently reacts with alliin to make the aforementioned component allicin. Of course, the evident ambiguity of all these terms makes the reaction somewhat difficult to comprehend, but from a wider perspective, it really is nothing we haven’t seen before. As a matter of fact, this conversion to allicin actually occurs when you cut or crush garlic with a knife! This explains the tear effect, as it is when garlic is cut that its bioactive component, allicin finally appears.

 The act of chopping or crushing garlic releases the allicin in the cloves of garlic.

Once the allicin is produced, it will take a short time for the odor from the garlic to go away. As it turns out, allicin has quite a short half-life (2.5 days at 23°C,  to be exact!). It can be assumed that the reaction is first order with respect to allicin, since the half-life is constant at certain temperatures and not dependent on the initial amount of allicin produced. This is convenient for the production of allicin, as it helps to maintain the preservation of alliinase and alliin so more future allicin can be produced. This allicin production occurs very quickly and within a small surface area of the clove (where the garlic is being cut), meanwhile the alliinase and alliin remain sustained in other parts of the clove. In other words, even though allicin generates a large amount of odor albeit briefly, as long as the alliinase and alliin persist in their respective section of the clove, then allicin can continue being made repeatedly.

Moving Forward with Allicin

In this video, a man gives a humorous account of how he tried to make allicin by directly consuming cloves of garlic.

Now knowing that allicin is produced when garlic is chopped or crushed, it would probably not be a very good idea to chew garlic directly, especially multiple cloves. Obviously, for the man in the video who tried to receive the effects of allicin directly in the body, it did not turn out too well as he received nausea as a result. There could be a possibility that this is why even though garlic powder does not contain allicin, it still achieves intense flavor and odor when consumed. Ingesting allicin in large amounts would cause potential uncomfortability in the body but not when derived into its chemicals such as alliinase and alliin as is with garlic powder in Flamin’ Hot Cheetos  and other garlic supplements in other food products. Garlic powder achieves similar effects to garlic but none that would be seriously detrimental to the body. With this, Flamin’ Hot Cheetos can acknowledge garlic powder’s contents for its intense heat, advantageously applying bioactive components of garlic for its effect. It is something to keep in mind for the next time you mindlessly munch on this interesting snack.

Even Katy Perry can’t deny the delicious taste of Flamin’ Hot Cheetos!


Chocolate. As addicting as it may be, ever wonder how chocolate comes to taste as amazing as it does? The rich and creamy taste of good sweetness in your mouth every time you take a bite out of your favorite chocolate bar just seems too irresistible. Or maybe you’re one of those people who prefer the aerated chocolate bars, infused with gas and is even creamier than regular chocolate. No matter your preference, the beautiful and unique taste of chocolate is due to the rigorous and complex processes it undergoes. Consistency is perfection and is tied directly to thermodynamics and the chemical compounds that are integral in the production of chocolate. From cacao bean to the bar you wish you were holding in your bar right now, let it be put that the perfect chocolate is not as easy to make as it may seem.

Figure 1. Theobroma cacoa, the cacao tree.

First, the cacao pods from the cacao tree Theobroma cacoa are harvested and the beans and pulp are extracted from the pod. They are left to ferment for a few days and then laid out in the sun to dry. Roasting the beans is one of the most important steps in making chocolate. It kills the lingering mold and bacteria (because that wouldn’t be too yummy to ingest now would it?) The roasting of the beans is also what changes the flavor and removes some of the bitterness. Now to the chemistry. The cacao bean  is comprised of 55% fat, 12% protein, 11% fiber and 6% starch. Roasting the beans removes fatty acids that are unwanted such as ethanoic acid. The roasting generates a chemical reaction called non-enzymatic browning, more specifically, the Maillard reaction. The Maillard reaction occurs when the carbonyl group of sugars reacts with the amino acid group and produces N-substituted glycosylamine and water. It then undergoes the Amadori rearrangement to form ketosamines that react further with brown nitrogenous polymers. The reactions of the Amadori rearrangement inclue mainly fission, dehydration, and degradation At this point, the beans have off-flavors and off aromas. But have no fear, these bitter and rancid-smelling beans do become the sweet chocolate we all enjoy and love through a few more processes. The beans are ground into cocoa liquor and then pressed to separate the liquor from solids. The solid is also known as cocoa butter and this key ingredient continues onto conching and tempering to become chocolate.

Conching  removes volatile compounds such as methanol and acetic acid, as well as adjust moisture content and viscosity. This is a mixing process that aerates the mixture for 24-60 hours at 110°F, to stimulate interactions between ingredients and molecules. As this occurs, flavor and aroma develop as acidity and the bitterness of the cocoa are lost and moisture content is reduced.

Tempering is but a complex cooling process, to make the cocoa butter seeds uniform in size and shape and to stack these molecules tightly together in a nice crystalline structure. Imagine a bunch of LEGOs, all different shapes and sizes. If piled together, it is not very efficient and unstable. But, if packed tightly and orderly, the structure is stable. The process of tempering is simply stacking cocoa butter seeds to be as stable as possible.

The main component of tempering is temperature. As the chocolate cools, the cocoa butter forms stable and unstable seed crystals. These crystals are proportional to the six different crystalline forms of cocoa butter. This means that the atoms are the same but they may be arranged differently. Relating back to LEGOs, there are many different types of arrangements but it will always be the same types of LEGOs you use to create something. The ability of having multiple arrangements or shapes is called polymorphism. It is found that the tastiest, most stable, and ideal form is Form V, or beta crystals. The melting point for the Form V polymorph is about 33.8°C, about 92.8°F. This temperature is about the temperature of a person’s mouth, unless they submerged their tongue in something cold for a long period of time. Because this polymorph’s melting point is nearly identical to our mouths’ internal temperature, chocolate basically spontaneously melts, which is chocolate is so irresistible. The lower the melting point of the polymorphs, the thicker and stickier it feels in the mouth. Polymorph VI, unfortunately, is produced after 4 months a room temperature, has a higher boiling point and is much more stable. Fats melt quickly because the carbon atoms within the fat form long chains of atoms. Intermolecular forces affect these chains, so the more fat chocolate has, the faster it melts due to the intermolecular forces caused by the carbon chains.

Figure 2. Different cocoa butter polymorphs and corresponding melting points.

Figure 3. Form V Polymorph

To keep only stable beta seed crystals, the chocolate is warmed again to a temperature between the melting point of beta crystals and the temperature at which beta crystals form. The mixture is then cooled at around 13-15°C, or 55-59°F, to promote preferential growth of the stable crystals. If the temperature were too high, the cocoa solids and other dry ingredients from the cocoa butter would separate, thus resulting in a dry paste. Likewise, if the chocolate’s moisture level increased even the slightest, the dry particles in the mixture would be saturated and detach from each other, maintaining a liquid form. Though this does not result in a chocolate bar, it is a useful technique to add water to chocolate when making chocolate sauces or syrups.

 Figure 4. Comparing the compactness and stability cocoa butter polymorphs.

Speaking of different forms of chocolate, believe it or not shape and type actually do contribute to taste. These are components that affect how the chocolate breaks up in the mouth, thus it is opinionated on whether you prefer a normal chocolate bar to an aerated one, for example. The cocoa crystals in chocolate are about 0.01 to 0.1mm in diameter. This microscale structure however varies slightly with the way the chocolate is molded. Normal chocolate bars are molded after tempering while aerated chocolates receive a blast of a certain propellant. These propellants can vary from nitrogen to argon to regular CO2 or even nitrous oxide, also known as laughing gas. This gas is infused into the chocolate and turns the chocolate into a foam with the use of a siphon. After siphoning, the chocolate is cooled in a low pressure environment, like a vacuum, to let the gas bubbles expand. Depending on the propellant used, the sizes of the bubbles also alter the taste of the chocolate.  A study funded by Nestlé proved that chocolate foamed with nitogen and nitrous oxide had more intense tastes due to the larger bubbles these gases produced.

Figure 5. A chef using a siphon to aerate chocolate into a foam.

“Aerated chocolate is more gentle and creamy. Its density is so low that it takes seconds for the chocolate to meld down in the mouth. That is why its taste is so exquisite and great,” says Stephen Becket, a former researcher for Nestlé. This is because aerated chocolate is lower in density and has a lower melting point, being only more sensational in the mouth and stimulating what is called mouthfeel. No wonder truffles seem to just melt into your soul whenever you pop one into your mouth. It’s always been about chemistry.

We can all admit that chocolate is an amazing sweet itself, whether it’s satisfying a crave or bestowing this great treasure upon a significant other on Valentine’s Day. What’s even more amazing is how chemical and mechanical processes are able to turn a bitter cacao bean into the beautiful joy that eating chocolate may bring us all. With these processes, the most important thing to keep in mind is consistency. Our senses are able to discriminate taste based on the texture of chocolate and its feel, and that’s pretty cool. Just think the next time you taste your favorite chocolate, think not only of how it became that perfect shape and texture but how because of the way it feels on your tongue, your taste buds cannot seem to thank you enough.

Crème de la Crème: Chemistry Behind Ice Cream and Whipped Cream

I scream; you scream; we all scream for ice cream! This very familiar rhyme is nostalgic for many, who instantly remember a much happier time in their lives. The sounds of children chasing an ice cream truck that constantly exudes kid-friendly tunes. To many, ice cream is a sweet treat savored on a hot summer’s day. Whipped cream, on the other hand, is a delectable addition at any time of the year. It could be sprayed on strawberries or atop a freshly baked pie. What you may not know, are all of the minute factors that make these forms of cream such an attraction.


Fat agglomeration examples

Fat destabilization, also known as fat agglomeration, is something that is necessary to create milkfat structures such as ice cream and whipped cream. Fat agglomeration is a general term referring to the different ways that fat globules destabilize and stabilize when undergoing different chemical reactions. This includes things such as flocculation and partial coalescence, both integral processes in the creation of cream substances. Flocculation is an irreversible clustering of fat globules, or particles. The way that these fat globules cluster can be explained by partial coalescence. This dictates that fat globules are combined and held together by fat crystals and liquid fat found in cream. Now that we have identified the fat globules found in cream, we can look deeper into how ice cream and whipped cream is actually formed.

Partially coalesced fat globules

When ice cream is made after the process of churning, the liquid ice cream is churned as it freezes until it’s as thick as softly whipped cream. While it is being churned, air is added so the ice cream has a greater volume. This is called emulsion, which will be further explored later. The main difference between ice cream and whipped cream is that ice cream is usually made from homogenized milk. Homogenized milk prevents creaming because it decreases the size of globules as well as even them out. Other ingredients are then added to ice cream to create its texture, such as salt. Milk does not freeze at 32°F like water, so salt is poured on the ice and the temperature reaches 0°F (-18°C) and it has a briny texture instead of having solid ice.

Think back to when you made ice cream in class using two plastic bags. There would be a larger bag that is full of ice and salt, and a smaller bag that contained the milk, sugar and vanilla. Then you put the smaller bag inside the bag of ice and shake. The liquid in the smaller bag begins to freeze if there is no salt added to the ice. Since salt is added to the ice, the ice will melt faster, preventing the bag containing the milk and sugar, from freezing, instead making a slushy texture. When it comes to churning ice cream, the whipping action causes the fat emulsion to break down partially and flocculate. The air bubbles that are being beaten are stabilized by partially coalesced fat. Without emulsifiers, the fat globules would resist the coalescing because of proteins being absorbed to the globule preventing air bubbles from stabilizing and the texture would not be smooth.

Fat structure in ice cream and creation of fat 3D network

Similarly to ice cream, whipped cream is formed due to a phenomenon called an emulsion. This is when air is suspended in a fatty liquid, the fat molecules being integral in stabilizing the solution. Since cream is 35-40% fat, when emulsified, it becomes whipped cream, or when the temperature is low enough, ice cream. But, this is not all there is to emulsion. In fact, the dictionary definition of emulsion is being able to combine two liquids that usually do not mix together due to effects of polarity. Fats, being a lipid, are non-polar. The non-polar hydrocarbon chains that make up fatty acids are hydrophobic, meaning they do not want to bond with water. Unlike fats, water is a polar molecule, having a partially positive and partially negative end. For an emulsion to occur, an emulsifier must be added to the solution of water and fat to make them bond together. The emulsifier for ice cream is different than that of whipped cream, simply because there’s different ingredients to create desired taste and these ingredients include different proteins. But once we have fat globules and an emulsifier, the whipping begins.


Whipping cream allows air bubbles to be integrated into the fat globules and then the cream partially coalesces. As mentioned previously, this is an irreversible clustering of fat globules held together by both fat crystals and liquid fat. The cream only becomes what we know as whipped cream due to emulsifiers such as lactose and other proteins that are trapped in the spaces between fat and air. A distinct protein found in milk is casein, which is dispersed in the form of micelles. Here is a quick video on the structure of micelles.

Though the specific structure of micelles is not fully understood, it is known to have a hydrophobic and a hydrophilic end. Because of the way micelles form, with the hydrophilic ends on the outside and the hydrophobic ends on the inside, the fat globules can now bond with each other and water, which end up being trapped between the fat globules and air alongside lactose and proteins.

Fat globule with and without emulsifier

Whether its ice cream or whipped cream, chemistry does a lot of work to be able to create these dairy delicacies. Each bite, filled with fat globules, air bubbles, casein micelles, lactose, salt, sugar, and many other different proteins and lipids that you probably have never heard of. Its not easy for cream to foam or freeze to satisfy your sweet tooth. So, the next time you taste a scoop of ice cream or top off your dessert with a dollop of whipped cream, thank fat agglomeration for the beauty of which is a product of pure chemistry and biological compounds.

Chemistry of Cooking: Milk!

Everyone has seen the large dairy aisle of their grocery store before: It is filled with all sorts of products that are necessary for almost any kind of cooking. There are so many kinds and types of milk! Other than the regular milk, there is skim milk, condensed milk, evaporated milk, and products made from milk like whipped cream, light cream, heavy cream, and buttermilk. Below, you can see the different kinds of milk we used in our tres leches (the recipe used can be found here). The name “tres leches” means “three milks” in Spanish, and it refers to evaporated milk, condensed milk, and heavy cream. Evaporated milk is simply milk that has been heated so that a lot of the water evaporates, leaving behind milk with a very thick consistency. Sweetened condensed milk is made in a similar fashion, but also includes a lot of sugar, which also makes the milk thicker.

Milk acts and tastes the way it does because of chemistry! More specifically, milk has properties of emulsions, colloids, molecular solutions, and ionic solutions, just to name a few. This is because milk contains fats, water, proteins, lactose, and salts, all of which have their own unique chemical properties. For a fun look at the chemistry of milk and other milk products, just keep reading!

Chemical structure of lactose

Lactose is the main sugar in milk and makes up about 4.9% of milk. Have you ever noticed that when milk is warmed, it tastes better? Thats because of the lactose! At higher temperatures, the lactose becomes more soluble in milk, which makes the milk taste sweeter. As for fats, there are over 400 different types of fats in milk. However, fats only make up about 3.4% of the composition of milk. Most of these fats are saturated, monounsaturated, or polyunsaturated. Saturated fats are non liquid fats like butter, while unsaturated fats are the liquid fats like oil. Milk is also made up of about 3.3% protein. All these proteins contain all 9 essential amino acids that humans need. Lastly, vitamins and minerals are probably what people know milk the most for. Do you hear people say to drink milk to make sure you are getting enough calcium? Well it’s true! Calcium is a major mineral in milk that helps keep your bones strong and healthy. Milk also has many other vitamins and minerals like vitamin A, vitamin B, vitamin C, magnesium, phosphate, and more!

One question you may have wondered about when shopping at the grocery store is where does skim milk come from? The answer is that skim milk comes from regular milk after some of the fat from the regular milk is “skimmed” off, reducing the amount of fat in the milk. To do this, the milk is left out to separate (it can also be placed in a centrifuge to speed up the process). The fat globules, which are less dense, rise to the top of the milk. This fatty layer can be easily skimmed off the top of the milk, leaving behind skim milk, with much less fat than regular milk. If not all of the fat is skimmed off, the milk may be categorized as 2% or 1% milk. The percentage is a measure of the amount of milkfat in the milk. The fat that is skimmed off the top of the milk actually forms cream, another common milk product. This separation of milk into cream and skim milk happens because milk is an emulsion of fat in water. That is, there are many tiny fat droplets inside a larger amount of water. The fat in milk can be found in tiny droplets inside a milk serum, and thin membranes surround the fat globules to separate them from the outer liquid. The fat is suspended in the milk, but with time, it can rise upwards.

Similarly, butter is an emulsion, but it is an emulsion of water in fat. This means that there are tiny droplets of water inside the fat. Butter is made by “churning” cream, either by hand or with machines, which basically breaks up the fat droplets that are suspended in the cream. The butterfat then clumps together again and separates from the rest of the milk.

Butter being churned. The liquid you see is the buttermilk.

What’s left behind after the butter is taken out of the milk is often called buttermilk. However, the buttermilk you see in stores doesn’t have a lot to do with butter at all. It is different from regular milk in that it has been set aside for a period of time and allowed to ferment. In fermentation, bacteria convert lactose into lactic acid. Lactic acid has a tangy flavor, which is something unique from milk that can make buttermilk favorable to milk in some kinds of cooking. When cooking with buttermilk, baking powder must be used differently, as the lactic acid is not acidic enough to fully react with the baking powder. In this case, baking soda would be easier to use. However, since the buttermilk does have some acidity, the amount of baking powder or soda that is needed is less than that would be needed when cooking with other substances.

There is another kind of milk that doesn’t come in a carton like many of the other milks do. Usually, it comes in a can. Its whipped cream! There is a specific chemistry that come with “whipping” cream. If you’ve ever tried to make whipped cream at home, you’ll know you have to use whipping cream, not light cream or milk. That’s because whipping cream has a specific fat content that makes it ideal for making whipped cream (specifically, 30% or higher). This is important because there needs to be enough fat in the milk to make the whipped cream. If there is not enough fat, the milk will not be able to “trap” air and cause the cream to be whipped. These fat molecules have the ability to join together and form weak bonds. When you “whip” whipped cream, what you’re really doing is incorporating a lot of air into the cream. These intermolecular bonds can trap the air and make tiny bubbles, which is what makes the whipped cream light and fluffy! Another thing to note is that canned, store-bought whipped cream is not made the same way as homemade whipped cream. In fact, rather than whipping the cream in the open air, companies will actually put nitrous oxide (NO), which isn’t normally in the atmosphere, into the cream. Due to their multiple electron shells, the nitrogen and oxygen act as dipolar molecules and will subsequently hydrogen bond with some of the fat molecules when the gas is whipped into the cream. This helps keep the whipped cream fluffy while it’s in the can.

Milk, like all other foods, gets old. Rotten milk is something that everyone hates to smell. Other than rotting, milk changes as it is left in the open, and this is descriptive of some changes in the milk that we can notice daily. When milk is left alone, fats inside of the solution can go through oxidation, creating a metallic flavor. Salts present in the milk accelerate this process, which could potentially be bad for the packaging and selling of milk around the world: both direct sunlight and fluorescent lights can activate the reaction. The addition of oxygen to a CH group in milk fat will create a hydroperoxide that changes properties of the milk. The off-flavor is prevented through pasteurization (heating the milk to a high temperature), which serves to counteract the oxidation reaction. This is why you’ll notice that almost all milk sold in stores is pasteurized. Another reaction in milk can be lipolysis, which occurs when the milk fats break down into glycerol and other free fatty acids. These free fatty acids, which consist of butyric and caproic acids, make the reacted fat smell and taste curdled and rancid. Sometimes, pasteurization can cause this reaction to be activated at high temperatures, so the packaging and treatment of milk can be very sensitive and more complicated than expected. Another thing you’ll notice in store bought milk is that it’s usually homogenized. Homogenization is a process of breaking up the fat globules in milk into smaller droplets that are evenly spread throughout the milk. This reduces the milk’s tendency to separate. This is usually done by forcing milk through tiny holes a high pressures, which causes the fat globules to break up.

Milk is something that mankind has been enjoying for centuries, even if we did not always know about its components and properties. The next time you go to the grocery store, look around at all the different ways milk has been used and modified! It’s amazing how many different products can be formed from something as commonplace as milk.

Antibiotics 101

Antibiotics, an introduction.  

Antibiotics are agents, either naturally occurring or synthetically produced, that kill microorganisms or inhibit their growth. This general definition allows for the further classifications of antibiotics, or antimicrobials, into classes that describe the specific microorganism that each compound targets.  Some examples of these classifications include antibacterials, antifungals, antivirals, and antiparasitics. These antibiotics have had a major impact in the medical community since their widespread usage began in the 1940s. One of the milestones in antibiotics that marked the beginning of its widespread usage was achieved by Ernst Chain and Howard Florey when they were able to develop a powdered form of penicillin by isolating its active ingredient. Penicillin remained at the forefront of antibiotics for decades and was known as the “miracle drug” because of its ability to cure people of previously fatal bacterial infections. So how exactly does penicillin work?

          Put simply, penicillin works by destroying the cell wall of bacteria. It does this by specifically targeting and inactivating the enzyme transpeptidase. Transpeptidase is responsible for the cross-linkage in the bacterial cell wall, and after a nucleophilic oxygen of the enzyme binds with penicillin rendering it inactive, the cell wall of the bacteria ruptures. For more on how this process occurs, check out this link.

          Antibiotics can be manufactured synthetically or semi-synthetically which means that they are unnatural drugs that can be made from non-living components. While semi-synthetic antibiotics are simply made by including an additional step that requires modification of the naturally produced chemicals, synthetic antibiotics are created with a new chemical manufacturing process. In order to understand how semi-synthetic and synthetic antibiotics are made, one must understand how natural antibiotics are made. A sterile and controlled environment is required to produce all kinds of antibiotics in order to prevent external contamination of the product. Natural antibiotics begin with a preparation of a culture of microorganisms. These cultures are constantly fed in fermentation tanks so that these microorganisms reproduce. After several days of supervising the process and controlling temperature, humidity, and other conditions, an antibiotic broth can be run through a filtration system so that it can be purified and the drug can be separated. After confirming that the product is not contaminated, it is ready to be sold worldwide. However, semi-synthetic drugs have a required additional step. Instead of purifying the natural product, it is put through a chemical process that alters the structure of the drug, thus making it not fully synthetic but not fully natural. These alterations of the structure are made in order to have a better effect on infecting organisms or to be better absorbed by the body. Synthetic antibiotics are simpler to produce because thesynthetic drugs are not subject to the natural variations found in living organisms that are used in fermentation tanks.

           There are many different types of semi-synthetic or synthetic antibiotics. For example, the first synthetically manufactured antibiotic is chloromycetin. This synthetically made antibiotic was used to treat ocular infections that involves the conjunctiva or cornea. However, chloromycetin is only used for serious infections when other weaker or less dangerous drugs are ineffective and therefore, chloromycetin is no longer available in the U.S. Ampicillin is a penicillin antibiotic that is derived from basic penicillin nucleus, 6-aminopenicillanic acid. This drug is used to treat infected areas such as urinary tracts. Erythromycin is another synthetically made antibiotic that is part of the macrolide antibiotics. Macrolide antibiotics slow the growth of bacteria by reducing the production of proteins needed by the bacteria to survive. This drug is mostly used by people who are allergic to penicillin. These examples of synthetically orsemi-synthetically made antibiotics are important contributors to treatment of infections of human bodies and are produced worldwide by manufacturers in order to meet the demands of patients.

          Traditionally bacteria are not resistant to antibiotics, in fact antibiotics are used to kill bacteria and other microorganisms. Bacteria tend to multiply by the billion as well as adapt and mutate often. Sometimes, these bacterial mutations make bacterium resistant to antibiotics therefore being harder to treat. Resistant bacteria that is not treated by antibiotics further multiplies. Antibiotic resistance leads to not only the misuse but also the overuse of antibiotics and vaccines which further leads to the creation of superbugsSuperbugs are formed when the gene that carries bacterial resistance is transferred or carried between bacteria so that there is a creation of bacteria with antibiotic resistant genes for many antibiotics. The most common types of superbugs are methicillin- resistant Staph aureus (MRSA) and multiple-drug or extensively drug resistant tuberculosis (MDR-TB and XDR-TB).

          Bleach is a commonly known disinfectant of bacteria. The active ingredient in bleach known as hypochlorous acid is what disinfects or causes the unfolding of proteins in bacteria which then clump together into a mass in living cells. This process is similar to the process of boiling an egg. The boiling process denaturizes the proteins of the bacteria in the egg making it safe to eat just as bleach does. As the bacterial proteins unfold, heat shock protein or Hsp33 is put into effect and protects proteins from the aggregation effect and further increases bacterial bleach resistance. Commonly, bleach’s base acidity also tends to compromise a bacteria’s lipid membrane, a process that is similar to the popping of a balloon. Overall, bleach is an extremely versatile disinfectant that kills a broad range of bacterium.

Check out this quick video on antibiotics in the meat industry.