Science and Cooking: From Haute Cuisine to Soft Matter Science - Viscosity and Polymers

As I posted in my October 13th blog entry, I've enrolled in an on-line course about the relationship between science and cooking.  I'm still plugging away at this, good thing I decided to do this for the knowledge and not the class credit.

Here's what went down for Week 7.

• Viscosity measures how easy something is to pour. Water has a low viscosity and cold syrup has a high viscosity.
• The molecules that make a liquid up flow past and bump into each other. To thicken it, we need to add molecules or particles that will impede the motion of the liquid.
• Want to measure the viscosity of a fluid, but you don't have a rheometer? If you have some free time on your hands (and who doesn't?), take a container and put a little hole in the bottom, and measure how long it takes for the fluid to flow through the hole.
• How thick or how thin a sauce is can make or break a recipe. Some of the ways to thicken food are:

1. Reduction: This term you've heard on your favourite cooking show means you take the material you want to thicken, heat it on a stove in an open pan, and you reduce it by simmering it until about half of the water has left, through evaporation. 
• This works because they were already enough molecules in the material you want to thicken to cause a thickening, but because of all the water molecules in the liquid, they were just too far apart to thicken. It works well if you have a stock, because it has lots of gelatin molecules. But it won't work if you just have something with only very small molecules in it. This is why you can't thicken a brine by boiling it, and why can't thicken wine by boiling it, unless you boil it all the way down till it's a glaze and there's almost nothing left.

Here is guest lecturer Carme Ruscalleda in her native Spanish to demonstrate:


2. Emulsion: Another oft-heard cooking show word, this is the process of combining two liquids (usually fat and water) that will maintain their distinct characteristics after being mixed. Common fat in water emulsifications include hollandaise sauce and mayonnaise, and common water in fat emulsifications are vinaigrettes and whole butter.
• Adding oil is a good way to thicken, but it makes what you're making taste of the oil you're using.
3. Starch-based thickener: This is a classic French technique of mixing and cooking equal parts flour and fat into something called a roux.
• The starch in the flour is heated up to the point that it hydrates and gelatinizes, turning the starch molecules into sticky polymers that make a liquid thick.
• Note that you have to cook the roux properly, otherwise it will have a floury taste, and it won't thicken well. You can use cornstarch or arrowroot or other starches, but if you put too much in, your roux will get rubbery and have an unpleasant texture.
4. Modernist thickener: These are substances used by those who worship at the altar of molecular gastronomy. Xanthan gum, a natural product, is made by fermenting a kind of bacteria. Because of the polymer molecules, very small amounts can produce a large increase in the viscosity of a liquid- in most foods, it is used at 0.5%, and can be used in lower concentrations. Xanthan gum also helps thicken commercial egg substitutes made from egg whites, to replace the fat and emulsifiers found in yolks, and is also used in gluten-free baking, as it gives the dough or batter a "stickiness" that would otherwise be achieved with gluten.
• A polymer is a very long, but very flexible molecule, made up of many, many monomers. Polymers have to get out of the way of one another in order for the fluid to flow. This is why polymer thickeners are so effective at increasing the viscosity of a fluid.

• Gels can also be used in thickening, as their long polymer molecules stick to each other, in a random way, trapping both water molecules and all other molecules, into something that effectively becomes a solid, like Jell-o. When you break them up, by pureeing it for example, the gel will reform slightly, and create a fluid gel, which acts like a thick liquid.
• Agar agar (or just agar) is a natural gelatin product made from seaweed that's been used for more than 1000 years in Asian cooking. Like xanthan gum, only a small amount of agar is needed to thicken your soups and sauces.
• Food additives like agar agar and xantha gum can be ordered online at MOLECULE-R.

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.

Science and Cooking: From Haute Cuisine to Soft Matter Science - Week 4

As I posted in my October 13th blog entry, I've enrolled in an on-line course about the relationship between science and cooking. It's been awhile since my last post about this course, for reasons that may or may not have to do with "Batman: Arkham Origins", and a neglected stack of laundry.

Here's what went down on the fourth week.

• This week the topic is elasticity, and one of the guest lecturers is White House Pastry Chef Bill Yosses.
• Who knew the White House had its own pastry chef? I wonder if either Barrack or Michelle has ever asked him to whip up a batch of cro-nuts for them.
• To measure elasticity, we are shown how it is measured with a spring. This principle of physics, called Hooke's law, states that the force needed to extend or compress a spring by some distance is proportional to that distance. That is, F = k x, where k is a constant factor characteristic of the spring, its stiffness.
• What does this have to do with food? Elasticity in food relates to how it feels in your mouth when you chew it. For example, the elasticity of a steak will increase as it becomes more difficult to chew the longer it is cooked.
• I had no idea there were different mouth feels for tofu, or that firm and soft tofu even existed.
• The mathematical description of an object or substance's tendency to be deformed elastically (i.e., non-permanently) when a force is applied to it is E = U over I³, where U is the interaction energy between the bonds in the material, and I is the distance between them. This is also the equation of the week in case you were wondering.
• We are treated to a scientific look at the making of strudel, which leads to a discussion about gluten, the protein that gives strudel dough its special characteristics.



• Did you know hearing plays a part in the enjoyment of food? Harold McGee talks about an experiment done at Oxford University where the subjects put on sound-blocking headphones, and  sat in front of a microphone, and bit into potato chips. The sound of the biting was picked up by the microphone and processed before the sound was passed back to the eaters' ears through the headphones. When the chewing sound was sent to the headphones unchanged, the eaters rated the chip as normally crisp. When the sound was amplified, they rated the chip as more crisp.
• McGee also mentions anthropologist Richard Wrangham's belief that because cooked food is often easier to chew, the invention of cooking has had a profound effect on the evolution of the human species.
• Dan Souza from America's Test Kitchen and Nathan Myhrvold of Modernist Cuisine fame both recommend slow-roasting tough cuts of meat, like an eye of round roast - who am I to argue?
• Poking your meat full of holes can make it be more juicy. This process is called jaccarding, and is done with a device not surprisingly called a Jaccard. A Jaccard has tiny blades that cuts little bits of the muscle fibers weakening the collagen fibres in them without cutting the meat totally. By poking the meat with holes, the collagen fibers do a less effective job squeezing the moisture out of the meat when it's being cooked.
• Note to self: Invest in a sous-vide machine so I can experience a short rib slow cooked for 72 hours.
• We end Week 4 with a summary of elasticity and another appearance by Bill Yosses, who demonstrates how, with a little sugar, water, and glucose, you can make a candy apple.

Science and Cooking: From Haute Cuisine to Soft Matter Science - Week 3

As I posted in my October 13th blog entry, I've enrolled in an on-line course about the relationship between science and cooking. A very video heavy week this time out - food porn fans would really appreciate all the detail that went into the making of this course. 

Here's what went down on the third week.

• The guest presenters this time out are Joan Roca, who runs the world-famous restaurant El Celler de Can Roca in Girona, Spain with his two brothers; and Dan Souza, senior editor for Cook's Illustrated Magazine, and current cast member of the America's Test Kitchen television show, radio program and podcast.
• This week we learned about the various phase transitions foods can go through in the cooking process. While a change in temperature can cause a phase transition, a change in pressure can also make this happen.
• A pressure cooker works by trapping some steam as water inside it boils, thus increasing the pressure and raising the boiling point. When the boiling water reaches this higher boiling point, it transfers heat to the food more quickly than water at just 100 degrees Celsius. This is a much better way to explain how a pressure cooker works than the method used to describe what happened in Boston back in April of this year.
• Want to cook the perfect egg, one with a temperature of about 64 degrees Celsius, perfectly every time? As water boils at a lower temperature as you gain altitude, just climb a tall enough mountain. Unfortunately, the boiling point of water on the top of Mount Everest is about 71 degrees Celsius, so you're going to need a bigger mountain.
• Chef Roca then demonstrates some of his renowned sous-vide cooking techniques by cooking, among other things, eggs and a fillet of sole.
  
  
  
  
• Another method to cause a phase transition is to use a rotovap, which is used in laboratories for the removal of solvents from samples by evaporation, and in cooking for the preparation of distillates and extracts. Check eBay for one if you ever need to distill the essence of something in one of your dishes.
  
• The concept of entropy has been introduced; I don't recall ever hearing about entropy in either elementary or high school science class, but I'm learning about it as part of a course about cooking, go figure.
• To be fair, I don't recall getting as much background in the half semesters of elementary school home-ec class either. Maybe it's time it should...
• Still haven't clapped for the equation of the week. This time it's U = CkBT.
• A chemical breakdown of fats and a discussion about the science of supercooling follows, along with an explanation of why you can't make water as salty as you can sweet. Thanks to this course, I now know that the solubility of any compound, is similar to the phase transition between a solid and a gas. 
• I scream, you scream, this week's lab involves the making of ice cream - sweet.