Welcome to summer! The sun is shining, it’s hot out and you have the beach on your mind. And we know what you’re craving to cool off—ice cream. This delicious treat comes in many different flavors and forms. There’s hard ice cream, soft serve, custards and sherbets. But have you ever though about how these varieties are created? We talked with American University’s Matt Hartings. Turns out the ice crystals in ice cream determine the consistency. “What you’re doing when you make creamy ice cream is you control the size of ice crystals in your ice cream. So we’re going to start off with this hexagonal shape for a growing ice crystal. As you go along you add more and more ice to the outside of your growing crystal. Eventually we get really large ice crystals.” So the bigger the crystal gets, the harder and crunchier your ice cream gets. If you don’t want to crunch on your summer treat, you want your ice crystals to be small. How do you do that? There are two ways: First, add an emulsifier. Ice cream is a mixture of water and fats. These two substances naturally want to separate. If they separate, like middle school kids at a dance, the water molecules will hang out by themselves on one side and will be more likely to form large crystals upon freezing due to their interaction. An emulsifier keeps the water molecules and fats mixed together, which keeps the water molecules away from each other, allowing for smaller ice crystals to form. The second way to control ice crystal formation is by changing how fast the water freezes. “If you freeze your ice crystals very quickly, you get lots of tiny crystals like this. If you let them freeze over a long period of time you get bigger and bigger crystals.” To prove that he’s not just all “sweet talk”, Matt made ice cream three different ways. First he made ice cream the old fashioned way—in an ice cream maker. “So what this does is there’s a heat exchanger in the middle. We get it really cold in the freezer…and this needs to freeze over the course of the day maybe
two days to get all the liquid inside this container really cold and what will happen is This will turn and churn the ice cream as it freezes it. And this will take about half an hour, so
obviously this is a long time. So our ice crystals out of this preparation will be a bit bigger than some of our other preparations.” “Another way to cool down our ice cream base is with salt and ice. Salt changes the freezing point of the water so we can get lower temperatures with this bag of ice right with salted in it.” Now we’re gonna play with liquid nitrogen. So what we want to do is pour slowly as we mix it up. so I’m mixing like I did in the dry ice for two reasons. One is when you make ice you want to keep incorporating air into the ice cream to help with the flavor and stability of the ice cream. But also because we want to quickly transfer the liquid nitrogen through our liquid to cool it evenly.” Sugar and fats plain crazy important
role in the flavor of ice cream. Cold tends to numb the tastebuds, so consuming cold ice cream dulls the sensitivity of the tongue. This is why ice cream has so much sugar in it. Try tasting melted ice cream and cold ice cream. The melted ice cream will taste significantly sweeter. As far as the fat goes, unless the ice cream is labeled as light, low-fat or nonfat, ice cream must contain at least 10%, fat from milk. Premium ice cream — You know, The really good stuff — has up to 20% fat, which gives it a velvety, rich texture. So we tasted the results and Matt was right. The “salt and ice” ice cream was the crunchiest, the “ice cream maker” ice cream was less crunchy, and the liquid nitrogen ice cream was incredibly creamy. Now we’re not saying you have to buy liquid nitrogen and start blasting your ice cream with it. But at least now you know why your creamy treats is so silky smooth. If you like learning cool things like this make sure to hit that subscribe button. And while you’re here, check out why bacon smells delicious or how artificial snow is made. For more ice cream chem, check out the ChemMatters article in the summary.