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 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.
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.
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.
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.