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| This pastry from Le Reve Patisserie in Wisconsin just may have gelation represented in two layers - in the fruit sauce on top and in the creamy center (if it's a Bavarian or Diplomat Cream stabilized with gelatin). |
If you got this far, you're nearly halfway through the Harvard online food science class and for that, Harvard offers you a sense of wonder. This is not the Jell-O shots class, far from it. Instead, you'll wander into the world of molecular gastronomy.
For starters, we all know about gelatin because we grew up eating jiggly things in bright colors. But how does Jell-O, Jell-O pudding or that fright tomato aspic work? In this week's terrific lectures and videos, you find out.
Suppose there's a liquid in your bowl, and you want to make it solid. That's no problem with eggs; they easily change into their omelet overcoat (and sometimes rubber shoes) when you apply heat. What if there is no heat? Could you still make the liquid change?
Gelation is your answer. It's a phase transition that turns a liquid into a solid by forming these little cross-links at the molecular level. And you need a critical number of these cross-links for a liquid to solidify. Think of cross-links as being like people in a room, reaching out with both hands to grasp each others' hands. The more hands being held, the tighter the network becomes and voila, a room full of people demonstrate what happens when a liquid changes to a solid. At first they can flow around like liquid. Soon they're into a game of Twister.
Ferran Adria of El Buli fame took gelation a step further with his concept of spherification. This is the idea that you could take a liquid, add something to it and create tiny spheres that have a solid membrane on the outside but remain liquid inside the sphere. And you could do it with different gelling agents - not just with gelatin but with natural ingredients derived from plants, seaweed, even bacteria. Zounds!
Imagine popping some of these gelled spheres in your mouth - think caviar - but once the sphere hits the warm tongue, the gelled edge gives way and you taste the sensation of the liquid inside the sphere. Via chemistry, which I leave to Harvard to explain, this is possible with foods you never dreamed of before. Spherification is like Grand Central Station, where science and cooking meet up under a great canopy.
We also need to understand the concept of diffusion, the motion of ions moving from one place to another. They do what's known as the "random walk," randomly switching directions but over time, making progress through Grand Central toward the exits. The equation that characterizes the progress is the Equation of the Week.
Equation of the Week: L = the square root of 4Dt. L is the distance the ions move; t is the time elapsed. D stands for a set diffusion constant measured in centimeters squared per second. For calcium in water, that diffusion constant number is
8 × 10−6 cm2/sec.
You can use this equation to predict the thickness of a spherification shell. Why? Because if you do nothing to stop the gelation process of your sphere, eventually you'll create a solid sphere, because gelation starts at the outer edge and moves toward the center.
A-Hah Moment of the Week: When you're making plain old eggs, you need some fat. A little half and half in your scrambled eggs has a huge effect on texture. That's because it slows down coagulation of the eggs when heat is applied, by coating the egg proteins. If you don't add fat, heat causes the protein strands to align and bond into a network - the more you heat, the more this happens. Eventually, this network squeezes out the available moisture and the eggs get clumpy and dry. You know this. You've eaten them before. Throwing in some cream works, but cream overwhelms the egg's flavor. Skim milk doesn't add enough fat to coat the protein strands. Half and half is just right if you want fluffy, marvelous eggs.
2nd A-Ha Moment of the Week: If you add salt to your eggs after scrambling them, they get rubbery. If you add salt before cooking them, the salt affects the electrical charge on the protein molecules, reducing their tendency to bond together and squeeze out the water. I see.
3rd A-Ha Moment of the Week: Add salt when sauteeing onions. If you don't, they brown too fast but remain crunchy on the inside. When you add salt, it draws moisture from the onions, and this moisture now released into the pan helps protect the onions against the heat. They'll brown more slowly.
Final A-Ha Moment of the Week: Did you know that paper towels are not food safe at high temps? Instead of using them in the microwave, try coffee filters. A-Ha!
Number of Pages of Notes: Stopped Counting
Next Week: Heat Transfer
You can use this equation to predict the thickness of a spherification shell. Why? Because if you do nothing to stop the gelation process of your sphere, eventually you'll create a solid sphere, because gelation starts at the outer edge and moves toward the center.
A-Hah Moment of the Week: When you're making plain old eggs, you need some fat. A little half and half in your scrambled eggs has a huge effect on texture. That's because it slows down coagulation of the eggs when heat is applied, by coating the egg proteins. If you don't add fat, heat causes the protein strands to align and bond into a network - the more you heat, the more this happens. Eventually, this network squeezes out the available moisture and the eggs get clumpy and dry. You know this. You've eaten them before. Throwing in some cream works, but cream overwhelms the egg's flavor. Skim milk doesn't add enough fat to coat the protein strands. Half and half is just right if you want fluffy, marvelous eggs.
2nd A-Ha Moment of the Week: If you add salt to your eggs after scrambling them, they get rubbery. If you add salt before cooking them, the salt affects the electrical charge on the protein molecules, reducing their tendency to bond together and squeeze out the water. I see.
3rd A-Ha Moment of the Week: Add salt when sauteeing onions. If you don't, they brown too fast but remain crunchy on the inside. When you add salt, it draws moisture from the onions, and this moisture now released into the pan helps protect the onions against the heat. They'll brown more slowly.
Final A-Ha Moment of the Week: Did you know that paper towels are not food safe at high temps? Instead of using them in the microwave, try coffee filters. A-Ha!
Number of Pages of Notes: Stopped Counting
Next Week: Heat Transfer
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