Jio Jeong's List: food & cooking

• When the temperature rises above the melting point, molecules leave the solid and enter the liquid at a faster rate than the molecules in the liquid crystallize onto the solid.
• The fat in cocoa beans (called cocoa butter) melts in a small temperature range, between 93 and 100 degrees Fahrenheit (34 to 38 Celsius). Normal human body temperature is in this range. So if the temperature is hot enough to melt chocolate, you body has a hard time staying cool, and you move into the shade.
• becomes a soft paste or liquid in the mouth.
• Other fats have different melting points. Tristearin is a hard waxy fat that melts at 154° F (68° C). Triolein, which has three kinks in the molecule, so it can’t form compact crystals as easily as tristearin, melts at 41° F (5° C).
• Cocoa butter has a mix of fats, but is made mostly from the fatty acids stearic acid, palmitic acid, and oleic acid, sometimes on the same glycerin molecule

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• The white of an egg is a transparent gel before cooking. The proteins are dissolved in water, but they have electrical charges on their surfaces that make them repel one another. This gives the liquid its gel form, and keeps much of the egg white in a high puddle around the egg yolk.
• almost watery protein solution
• As we heat the egg white, some of the proteins denature sooner than others (at a lower temperature). As the proteins unfold, the electrical charges that were on the inside are available to form bonds on the outside.
• Instead of a transparent gel, the egg proteins become as white as clouds

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• why chocolate melts. Butter is similar
• melt when a rise in temperature shifts the equilibrium between melting and solidifying. Butter, like chocolate, contains a mixture of fats. But butter has a wider mix of different fats, and doesn’t melt at a particular temperature all at once. Butter softens over a range of temperatures, until finally a temperature is reached where it is almost entirely liquid.
• Butter is an emulsion of tiny water droplets inside of the fat. Each droplet is completely surrounded by fat, and the fat forms a continuous coating over all of the water droplets. Like soap bubbles and the bubbles in bread and cookies, a surfactant molecule (in this case milk protein) keeps one end in the water and the other end in the fat, stabilizing the droplet and preventing it from joining other droplets.
• This keeps the butter from separating into a layer of water and a layer of fat.

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• Actually, plain sugar doesn’t stay in your mouth long enough to feed the bacteria that inhabit the film on your teeth
• . But foods such as dried fruits and many candies, which have sticky particles that slowly dissolve, will cause the bacteria to grow.
• Your teeth are coated with a thin layer of material called plaque. This material is formed by bacteria in the mouth, which glue themselves to your teeth to avoid being swallowed.
• bacteria eat sugar. When they eat the sugar, they produce acids. The bacteria do not eat your teeth, but the acids do dissolve tooth material if they accumulate enough to raise the acidity levels enough. It takes the bacteria about 20 seconds to convert sugar into acid, and the acid stays trapped in the plaque next to the teeth for about a half hour.
• It is not the amount of sugar that is important, but how often you eat sugar

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• Living things need enzymes to do their job. Enzymes are proteins that use their particular shape to guide chemical reactions. If something changes that shape from its natural form, we call it denaturing the protein. A denatured enzyme usually does not work properly.
• One way to denature enzymes is to heat them. When we seal food in cans, we then heat them, to denature all of the enzymes inside. That kills the bacteria and molds, since they need their enzymes to survive. And it also denatures the enzymes in the food, which would otherwise cause the food to break down into an unappetizing mush. It is enzymes that cause fruit to bruise, and meat to spoil.

• A chemist knows that green vegetables turn an ugly drab color when the magnesium atom at the center of the chlorophyll molecule is replaced by a hydrogen atom. This can happen when green vegetables are heated, or when an acid is present.

• Complex chemical reactions go on in food all of the time – even if you’re not cooking them. Some of these reactions make food go off.

   

  For example, bananas turn brown because a hormone within them triggers the release of ethylene gas (C2H4). This accelerates the ripening processes until the banana becomes over-ripe.
• Ethylene has an accomplice called polyphenol oxidase (or PPO for short). It’s found in apples and potatoes, so leaving your banana next to an apple will hasten the ripening process
• Meat is animal muscle, 75% of which is water. The rest is protein (about 20%) and fat (5%), as well as small amounts of carbohydrates, acids and minerals.
• • The protein molecules are in bonded coils, but as heat is applied the bonds break and the coils start to unwind.
   
  • Meanwhile much of the water content in the muscle fibres leaches out – that’s why your fillet steak or chicken breast is smaller after cooking than when it is raw.
   
  • If it’s red meat (lamb, beef) it begins to turn brown as the myoglobin reacts to the heat. Similar to haemoglobin, myoglobin is a protein that stores oxygen in red blood cells. Heat triggers iron atom oxidation. The iron atoms in the protein lose an electron and this gradually changes the colour from red to brown.

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• Digestion; enzymes promoting chemical reactions that power our bodies. Lifting your arm requires your body to make and burn ATP using oxygen with carbon dioxide as one of the waste gases produced.
• The internal combustion engine takes liquid gasoline, converts it to a gas, burns it takes the waste to make mechanical energy and then expels some noxious gases. The rare metals in the catalytic converter scrub out the sulfuric acid, but we still get the ingredients for smog out of them.
• like rising bread we have an actual chemical reaction where the yeast changes the food.
• When concrete dries and hardens the water actually causes a chemical reaction with the cement making a binding action drying concrete isn't just losing water it is undergoing a chemical change and one that creates heat as well (an exothermic reaction).
• When you write with ink on paper, the ink and paper unite in a chemical reaction so that you can't erase it. Specialized inks allow a short period where you can erase some inks, but most inks dry and can't be erased; they have bound with the paper. This includes your pen and your ink jet printer.

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• Flavor is a complex science. It depends on the interaction of a wide variety of physical and chemical properties in the food you're eating (not to mention the unique sensitivities of your nose and taste buds)
• if you heat something, its physical and chemical properties may change. That's why cooked food tastes different from raw food, and re-heated food often tastes different from food that's been cooked only once