Food science is a hot topic; one that David Joachim and Andrew Schloss explore with creativity and clarity in their lastest book The Science of Good Food.
And we're not the only ones who think so. David and Andrew won an IACP award in the Food Reference & Technical category and they are now nominated for a James Beard Award in the Reference and Scholarship category.
Last month, David and Andrew's IACP inspired guest blog on Project Foodie explored Alcohol and Water, today they share their 'food science' knowledge on one of everyone's favorites treats - ice cream...
Ice Cream is Cool
Think about how many flavors go well with cream. Mushrooms. Herbs. Hundreds of them! Now think about how many flavors pair well with eggs. Bacon. Toast. Hundreds more. If ice cream is merely frozen cream, sometimes incorporating egg yolks for custard-style ice cream, then it's easy to see why ice cream flavors are nearly infinite. That also explains why chef Heston Blumenthal's bacon-and-egg ice cream works so well.
But we'd rather discuss texture. The real draw of ice cream is its smooth, sensuous feel in the mouth. Achieving a creamy texture in ice cream is much more difficult than dreaming up novel flavor combinations. Here's why. Ice cream consists primarily of water (in milk and cream), which forms larger and larger ice crystals as it freezes. The bigger the crystals, the "grainier" the texture. The chef's art lies in manipulating the ice crystals to keep them small and undetectable.
Ice cream's basic ingredients are milk and cream (usually equal parts to yield about 17% milkfat), sugar (typically 15%) and flavoring. Reduced-fat, light, nonfat and budget ice creams contain less milkfat and more gums and emulsifiers such as carrageenan (derived from seaweed) to thicken the ingredients and mimic milkfat's smooth texture. When the basic ingredients are stirred or churned, they form an emulsion of ice, fat, and air. The trick is to freeze the mixture without it petrifying into a block of solid ice. Adding sugar and/or alcohol, stirring constantly, and freezing quickly all help to minimize crystallization and create a smooth texture in ice cream.
Sugar and alcohol work by reducing the mixture's freezing point below the freezing point of water, meaning the mixture will not freeze as hard. Some chefs also use invert sugar (sucrose broken into its component sugars, fructose and glucose) or liquid sweeteners like corn syrup to interfere with crystal formation and help create a smoother texture.
Constant stirring interrupts crystallization by incorporating air. Air breaks up the crystalline structure, making it less solid and lighter in texture. Air also makes ice cream easier to scoop and higher in volume. The volume in excess of the original mixture's volume is called overrun by ice cream manufacturers. In reduced-fat and very fluffy ice creams such as soft-serve, the overrun can be as high as 100%, which means the ice cream is half air. Generally, premium ice cream contains less air and more cream and sugar. These ice creams use freezing and mixing techniques for smoothness. Some manufacturers create small ice and fat crystals by extruding the ice cream mixture at about 5ºF (known as slow-churning); others partially aerate the mixture prior to freezing then recirculate it through a continuous freezer (known as double-churning). A few manufacturers have experimented with genetically altered proteins similar to those in deep-ocean fish that help to keep water in the ice cream mixture from crystallizing. Either way, quick freezing is essential for smooth ice cream because the faster the water freezes, the less time there is for it to form large ice crystals and a grainy, crystalline texture.
That's one reason why liquid nitrogen (LN2) has become popular for flash-freezing ice cream. LN2 boils at -321ºF. It is super-cold. Stir some LN2 into an ice cream mixture and you'll have ice cream in seconds. Try it yourself with the recipe below.
If texture is the first thing we love about ice cream, temperature is the second. Here are two interesting facts about ice cream and temperature:
1. The Mpemba Effect: You might think that a cold ice cream mixture freezes faster than a hot one. But many experiments have disproved this assumption. Aristotle first described the phenomenon with hot and cold water, and in 1963 an African high school student named Erasto Mpemba rediscovered it. While making ice cream, Mpemba fell behind his fellow science students and hastily stuck his hot ice cream mixture in the freezer. His ice cream froze faster than the cooled mixtures of the other students. Since then hundreds of controlled experiments have repeated the phenomenon with various liquid mixtures and offered a few explanations. The most intriguing answer involves temperature itself. Heat is energy in motion and freezing begins with tiny "seed" crystals on which larger ice crystals grow. Seed crystals form around impurities in the liquid or from agitation, which is essentially a state of motion. Knowing that the molecules in hot liquids are moving faster than the molecules in cold liquids, it makes sense that hot liquids will form seed crystals sooner and ultimately freeze faster than the slow-moving molecules in cold liquids.
2. Brain Freeze: When you press ice cream against the roof of your mouth to melt it, the hard palate gets super cold, and the surrounding blood vessels constrict. After you swallow, the blood vessels relax and open, resulting in massive dilation of the arteries that supply the palate. The adjacent nerves sense this dilation as pain and transmit a sensation of pain through the nerve that runs across your forehead, behind your eyes, and along your jaw - brain freeze. Even though brain freeze is preceded by extreme cold, it is actually triggered as the mouth recovers. It should be called brain thaw. To keep it at bay, slow down the thawing process by drinking something cold like a glass of cool water right after eating ice cream.
LN2 Basil Ricotta Ice Cream
Liquid nitrogen is available at welding supply and medical supply stores and is not expensive. However, it must be transported in either a pressurized tank or a specialized thermos, which can be pricy. Working with LN2 is about as risky as working with a deep-fat fryer filled with boiling oil. If it touches you, it will do some damage. Take care by wearing protective goggles, heavy rubber gloves, long sleeves, long pants, and closed shoes.
- 2 cups whipping (35%) cream / 500 mL
- 1-1/2 cups granulated sugar / 375 mL
- 1 cup chopped fresh basil leaves / 250 mL
- Pinch salt
- 1 container (15 oz/425 g) whole-milk ricotta cheese
- 1 tsp vanilla extract / 5 mL
- 3 quarts liquid nitrogen / 3 L
1. In a large saucepan, over medium heat, bring cream, sugar, basil and salt to a simmer, stirring often until sugar dissolves. Set aside for 5 minutes and strain to remove basil.
Disclosure: Review copies of books discussed in this post may have been provided to Project Foodie by publicists and/or publishers.
2. In a food processor puree ricotta cheese, basil-infused cream and vanilla until smooth. Transfer to a large metal or plastic bowl.
3. Put on the safety goggles and gloves and slowly add a small amount of liquid nitrogen as you stir with a whisk. Nitrogen gas will rise from the bowl as you stir. Don't worry; it won't hurt you.
4. Continue stirring and adding LN2 until the mixture thickens too much to use the whisk. Switch to a wooden spoon (or a stand mixer fitted with the paddle attachment) and mix thoroughly until the ice cream is firm, adding more LN2 as needed. Remove the spoon (or lift the paddle) and add the remaining LN2 to harden the mound of ice cream. Let stand a minute or two then pick up a spoon and dig in. Or pack into a tightly covered container and freeze for up to 48 hours. Scoop and enjoy.
Makes 1 quart (1 L)
Adapted with permission from The Science of Good Food by David Joachim and Andrew Schloss.