Science and Cooking: From Haute Cuisine to Soft Matter Science - Week 5

As I posted in my October 13th blog entry, I've enrolled in an on-line course about the relationship between science and cooking.  Yes, I'm still plugging away at this, luckily I decided to do this for the knowledge as opposed to the college credit.

• This week the focus is on gelation, diffusion and spherification. Appearances will be made by Nathan Myhrvold, José Andrés, and Ferran Adrià, who popularized spherification, the ability to create a small shell of gel around food.
• Spherification happens when sodium alginate, a polymer that comes from seaweed, reacts with a salt like calcium chloride. The polymers, when in solution, are negatively charged. Electrical charges that are negative repel each other. Calcium ions have two positive charges, which allows the calcium ions to stick to the alginate molecule, as one of the positive charges will cancel out the negative charge, but still leaves a positive charge left. That positive charge can then stick to another alginate molecule, thus allowing the two molecules to stick to each other. If the number of such cross-links becomes high enough, you then create a gel.
• Got some clementines laying around? This is what José Andrés would do with them:
  
• A common example of gelation - making jell-o, or cooking eggs. They consist of polymers with cross-links holding the polymers to each other.
• Polymers are long strands that are intermixed with each other.  Think of them as being like a bowl of spaghetti.  When you form a gel, you stabilize the cross-links between the strands, the cross-links being the places where the strands overlap. Only a tiny part of the material actually are the molecules that cause the solid to hang together. Most of it is actually liquid. That's why it's not as solid as your hand.
• The equation E equals kT over l cubed, can be used to find the elasticity of a gel.
• There are two categories of how cross-links can form. In the first category, the polymers come from some protein component of the food. This is what happens with eggs. The proteins unfold because of heating, and then they stick to each other forming cross-links.
• The second category involves some other binding agent being added, like a type of glue, that causes the polymers to stick to each other.
• Nathan Myhvold comes on to talk about modern thickeners, like agar, xanthan gum and gellan gum.
• A great practical use for all this knowledge of gels is make great scrambled eggs. Dan Souza demonstrates:
  
• Harold McGee talks about the history of gels and jellies, and mentions an imitation egg recipe used during the time of fasting during Lent in 1600.
• Ever wonder why your homemade coleslaw gets watery? A cabbage is about 93% water, and some of this water dilutes the dressing used on it.  It's the salty ingredients in the dressing that are drawing water out of the cabbage and ruining the coleslaw. When salt is applied to any vegetable, including cabbage, it creates a higher ion concentration at the surface than exists deep within the cells. The salt slowly diffuses into the vegetable while also drawing moisture out.  To equalize the concentration levels, the water within the cells is drawn out to the permeable cell walls. This process is called osmosis.
• To get rid of that moisture, toss your shredded cabbage with a teaspoon of salt in a colander, and let the cabbage sit for at least an hour or up to 4 hours until it wilts. Rinse the cabbage under cold running water, and press, but not squeeze, to drain, and then pat dry with paper towels. Then combine your dressing as normal.