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