Week 5: Diffusion, Gelation, Spherification

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

Week 4: Elasticity, Harvard Style

Measure the elasticity of rising rolls and again after the rolls are baked for a lesson in stress and strain, really!

For Week 4 of the Harvard online food science class, get yourself a rock. Bang it against your head, share it with the other rocks in your head or use it as a weight to measure the elasticity of a steak. The correct answer in this situation is all of the above.

Harvard wants you to know there's more to enjoying delicious food than just taste. There's also the enjoyment of mouthfeel - or texture. The concept of elasticity is one of the ways you can think about mouthfeel in scientific terms.

Here we meet the "elastic modulus," a way to measure a food's elasticity by exerting force on it (what ho, the physics). This tells you how stiff or soft a food is. What determines elasticity? The energy of the bonds in the food and the density of the bonds, or the distance between them. That right there is a mouthful. Think of it this way: When you cook food, you affect both the energy present in the food and the distance between the food's bonds. Doing so changes its texture.

What it means is, the more you cook a steak at high temperature, the harder to chew it is and the higher its elasticity. You can calculate this elasticity using a rock. No explanation follows here; my notes go on for pages of mathematical gymnastics. It is at this stage I knew I had to get a math/chemistry/physics tutor from here on. (Shout-out to Highland Park's own Dr. Stanton Ballard)

Equation of the week: E = Stress divided by strain = force/area, divided by the change in the length, divided by original length. Chew on that.

In simple terms, it's not how you deform the food in whatever way you cook it, but how you change the length of the bonds in the food. The shorter the distance between the bonds, the higher the elasticity, and the more the chew.

Ahah! Moment of the Week: Salt is important in bread dough and supports gluten development, but why? Salt, or sodium chloride, has positive sodium ions and negative chloride ions. These charges are attracted by the charged amino acids in the flour's glutenin protein strands. As glutenin strands begin to stack up next to each other, the positive sodium ions are attracted to the negative amino acids, neutralizing them. This means as the strands come closer together, they don't repel and gluten is formed. Salt of the world! It really matters.

A Ratio to Love: 1-1-1-1
1 part flour, 1 part sugar, 1 part egg white take 1 minute to bake into an angel food cake (in the microwave, using a paper cup).

Number of Note Pages: 21

Next Week: Diffusion and Spherification

Week 3: Phase Transitions, Harvard Style

Tarts can be an example of phase transition as the fillings change from liquid to solid forms.

Phase Transitions

The boss at Chez John declared my previous post on Energy, Temperature and Heat a review that crossed his eyes. He's got a point; a lot of this food science is food for thought, and some of it's bitter to swallow. Then along comes an aha! moment and you feel better. Here was one of my first in the Harvard course.

Aha! Moment With Alcohol: Why do we add vanilla or liqueur after a recipe has been heated and begins to cool? We say well, the alcohol would evaporate, but do you know why it does? Turns out that ethanol (pure alcohol) is liquid at room temp, and this is why we can pour ourselves a gin martini while thinking about the problem. However at 78 Celsius (about 172.4 degrees fahrenheit), it becomes a gas. That's why it might evaporate if your liquid is too hot. And that's the lead-in to phase transitions. Ethanol changes from a liquid to a gas. Voila!

Phase transitions happen when a substance changes from one state to another (solid, liquid or gas).

To get into this further, enter Chef Joan Roca, who some say is the No.1 chef in the world. Mon dieu!

Joan Roca shows you how to transform eggs, sole filet and anemones all through sous-vide cooking. Yep, some of the Harvard lectures are in languages other than English, but each includes a transcript so you can watch and read along.

Tool that's new to me: The rotovap (rotary evaporator). It's used to concentrate flavors in foods, freeze-dry foods at very low temperatures and separate dangerous, volatile compounds like methanol from cocktails. It does this by creating a vacuum, and that lowers the pressure around the food. (So the opposite of the rotovap is a pressure cooker.)

No. 3 Equation of the Week: U interaction = C x kbT

This formula represents the physical balance between the fact that molecules like to stick together (stay solid) and also like to jiggle around and evaporate off. There are many ways to change phases of food from solid and liquid to gas. You know one of them - temperature - but another is pressure (which happens by raising pressure in a pressure cooker, or lowering it in a rotovap. See, you just learned this if you made it this far).

Cool lab experiment: Yes, you can make a small amount of ice cream in a baggie, just following directions and using your hands - no ice cream crank at all. It's a demo of how a liquid turns into a solid - and that's a phase transition!

Number of Pages of Notes: 21
(am I improving on note-taking?)

Next up: Elasticity in Week 4, and if you think it's all about stretchy dough, not so fast.

Week 2: Energy, Temperature, Heat - Harvard Style

Harvard Online Food Science

We all know that heat is a form of energy, and energy causes change. Whether you make a creme brulee, filet mignon or sourdough loaf, how much change depends on things you can quantify.

So right off, we learn the Equation of the Week: Q = mcp delta t

That's a nifty formula that means the amount of heat needed to increase the temperature of a food depends on a specific heat constant of a material. OK, hold that thought.

Q is the amount of heat dumped into the food and is measured in joules. M stands for the mass of the food (its weight using a scale), measured in kilograms. Delta t is the temperature difference between where you started (like room temperature) and the food's final temperature (use Celsius, be cool). CP is the specific heat of material, a number that characterizes how much something heats up when you apply specific heat. It's measured in joules per kilogram.

A grand answer machine. Don't know how to find a specific heat or convert these units into other units? Use Wolfram Alpha, a computational knowledge engine that calculates for you. Bookmark it. You'll use it.

Know this: There is a direct relationship between the amount of heat applied and how much the temperature rises, that's all we're saying with this formula.

The message here is to learn what it takes to control variables for consistency so you get the same results every time. Observe and understand how ingredients function. You can't push to the next level in cooking just by switching ingredients on a technique. Learning cooking goes much deeper - understanding how new technologies and science relate to cooking. There has to be a reason to apply the knowledge, not just throw the science at whatever you're doing.

Dave Arnold of the New York bar Booker and Dax gives a terrific demo on how to make a campari and soda. Is there a better way to talk science than showing how to get those crazy bubbles into a cocktail? Dave spent years teaching other chefs how to apply new technologies and techniques; he's a lab master. In another eye-popping demo, he forces coffee into rum using nitrous infusion. This is the kind of stuff we should be showing students to fire the imagination for food science. (I'm advocating the art of the science here, not the consumption of alcohol.)

Cool point: Champagne flutes have low surface area to volume ratio, so they don't lose as much bubbles over time. That means, serve your bubbles in long, slender glasses, not those cuppy glasses in the movies.

Takeaway lesson: The most important innovation in cooking technology is lower-temperature cooking. The real revolution is in temperature control via tools like the immersion circulator. It keeps water accurately heated to a set temperature well below boiling - and that's how you get a perfectly cooked egg - by boiling it longer at 64 degrees instead of 212. Now sous-vide cooking begins to intrigue me. More on that as we move on.

Number of pages of notes taken: 34, an increase of 12 pages over Week 1
(but I rewrite all the math problems to "bake in" the concepts)

Up next: Phase Transitions in Week 3

Week 1: Fooding With My Mind: Harvard Style

If you want to build a better chocolate chip cookie, you'll have to learn how to compute the number of molecules in baking soda using Avogadro's number (6.02214129(27)×10²³ mol). Then calculate how much carbon dioxide the baking soda will produce in a chocolate chip recipe.

That's just a taste of a free online course through Harvard: From Haute Cuisine to Soft Matter Science. Will you learn amazing truths? Absolutely. Is there a killer molten chocolate lava cake recipe waiting to be discovered, a better french fry, perfect scrambled eggs? Oh yes.

Can you do the math for chemistry, physics and engineering concepts as they relate to food? Does your calculator handle big numbers? Can you grab a study buddy who loves this stuff? If the math is a deal-breaker (I understand, believe me), audit the class. Give it the old college try. Learning enlightens the soul (and food will lift your spirits).

The weekly lectures are insightful and full of "a-hah!" moments - as you would expect from Harvard. There are top-tier chefs too famous and too many to mention, but you've heard of Ferran Adria of El Buli fame? He's part of the lecture series. Supplementary reading comes from Harold McGee's "On Food and Cooking: The Science and Lore of the Kitchen." 

Note to self: Buttering the inside of a ramekin and sprinkling it with sugar does NOT give the souffle something to cling to as it rises, says McGee. Stop saying this in my French pastry classes.

Many giants in the industry lend their expertise, demonstrating techniques you've likely heard of but never seen - like popping marshmallows into liquid nitrogen, then straight into the mouth; carbonating cocktails; using gelation to make olive oil gummies. Sous-vide tricks. Explained!

For an easy overview to fire your interest, here are my takeaways, starting with the first week.

Week 1: 

Heavy on the history of food science, with a good anecdote about German chemist  Justus von Liebig, who accidentally changed the way the world cooked steak. He believed the juices mattered more than the meat fibers, deciding one must cauterize the steak with high heat to seal in the juices. Even the French went along with it; today we take a much gentler view of how to treat both fibers and juices to avoid shoe leather.

You'll hear of Sir Benjamin Thompson, Count Rumford; he invented the modern oven. There's the turn of the century Poison Squad - tasked with eating some of the most commonly used food additives to study the effects. (One wonders if they had T-shirts with the words "None but the brave can eat the fare.") Members would eat increasing amounts of an additive, tracking the impact on their bodies until they started to get sick. Read more in the Esquire article The Poison Squad: An Incredible History.

You'll learn how new thoughts and ideas developed - from how to finish sauces with meat extracts to the first electric blender. You'll take the journey from cooking via the bounty of nature to Adria's bounty of the imagination.

You'll mull the first Equation of the Week (in a collection of 10 equations): 1 mole = 6.022 x 10²³ molecules.

Each week, you'll discover a new equation that typifies the main concepts presented, and you'll work through problems using that equation. There are mini quizzes, weekly homework problems and labs. No tests. Memorize that.

Number of pages of notes I took in the first week: 22 
(awright, so I don't know a molar mass from a molecule).

Next up: Energy, temperature and heat in Week 2.