Hi! everyone:
I have revised the text for tomorrow’s practice as follows. I would like you read this in advance and prepare to talk about cooking mysteries which you surely enjoy.
Octane (Akira Oku)
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2015-4-18, Kyoto NHK ESS Practice prepared by Octane
Kitchen Chemistry, (partial revision of ACS materials)
Hello, everyone. Welcome to the practice program on April 18.
Do you like cooking? Sure you do, so, we shall look at some chemical transformations that take place when you cook. Cooking is essentially a chemical process, and the change in chemical properties in the materials changes the physical nature of them.
Today’s procedure.
(1) Read as many sessions A through D as possible (15 min). Recommended is that you finish reading the following recipes for sweet potatoes, meringue, boiled eggs and French fries before that day so that you can save reading time.
(2) Figure out the chemistry involved in the cooking procedure (10 min).
(3) Just imagine you are a skilled chef and prepare answers to the question below.
Questions: (Answer at least two questions to the people in your group.)
1. Regardless you like it or not, you are supposed to cook sweet potatoes by any mean such as boiling, whipping, baking or the combination. Read session A and explain the chemical change that occurs during the cooking of your choice.
2. If you are nuts about shortcake, you sure love its sweet and foamy cream. Read session B first, then, explain what you understand about the chemistry or else how to make a fancy meringue cream on top of the cake.
3. Which do you like fried eggs, boiled eggs or scrambled eggs? Actually I love scrambled, but today, just imagine you prefer boiled eggs. Read session C and explain how you can cook the best boiled eggs based on what you have learnt about the chemistry involved there.
4. Did you ever challenge cooking brown French fries like McDonald’s? To find out the mystery of McDonald’s, read first session D. Then, explain to your colleagues orally how you can make McDonald’s French fries or alike by extending your chemical knowledge you have just learnt.
Session A. Sweet sweet potatoes
I love sweet potatoes baked, boiled (not really, for reasons to be seen), and even whipped and seasoned. My most liked method to cook them is just to scrub them with a nylon net scrubber, wrap them in foil, and bake them. Sounds simple, right? It is not.
Sweet potatoes store energy as starch in the tuber, and as it cooks some of that starch is converted to sugar by enzymes. The problem is that the enzymes that convert the starch to sugar are extremely sensitive to temperature extremes. This enzyme starts becoming active at about 135 degrees F (57 ºC), and is destroyed at around 170 degrees F (77 ºC, temperature conversion: C = (F – 32) x 5/9).
This has serious cooking implications. "Regular" potatoes are usually baked at around 205 ºC, or boiled at 100 ºC at sea level, and we unfortunately have copied that technique for sweet potatoes. Since very little starch is converted to sugar when cooking regular ones, fast cooking is fine. Not so with a sweet potato, but that makes the preparation take longer. Here is what to do.
To bake them, put them in an oven preheated to as low as your oven will allow. My oven has 77 ºC as its lowest temperature. I say preheated because during the preheat process, local temperatures can rise well above the dialed in setting. Scrub and wrap in foil your sweet potato and place it in the 77 ºC oven, or as low as it will go, and keep it there for an hour, give or take, depending on how thick it is, and then ramp the temperature up to 205 ºC until it is soft. I know that I said that the enzyme is denatured at 77 ºC, but because heat transfer is so slow with the dry heat of an oven, it takes a LONG time for any part of it to reach that temperature.
If you are "boiling" them, do not. Do not even simmer them. You need a kitchen thermometer to do this well. Take a pan of water, whatever size you need depending on the amount that you are cooking, and bring the water temperature to 65 ºC. Then add your sweet potatoes and hold the temperature there for half an hour. Since water transfers heat much more efficiently than does the air, half an hour is enough. I prefer to cook mine in their jackets to prevent loss of sugar into the cooking water, but you can peel and slice them first if you prefer. It is a matter of taste. For peeled and sliced ones, 15 minutes will do. Then crank the heat up to a simmer (a rolling boil is just too hot), and simmer until tender. Thus you will have as sweet as a sweet potato as can be had, UNLESS you make the mistake of storing them in the refrigerator.
Session B. Copper and Meringue
This one is factually correct. It turns out that copper ions interact with the protein in egg whites to make an easier to fluff mixture. It turns out that the proteins in egg white, aka albumin, is rife with sulfur bridges that tend to keep them integrated, rather than making a nice foam. Copper "caps" those disulfide bonds, thus breaking them, making the molecules a bit smaller and more amenable for air incorporation. This is not really a big deal now with power mixers, but if you use a whisk makes a difference.
My personal experience indicates that it really does not matter if you use a power mixer, even a cheap hand held one. The action of those to incorporate air overcomes the slow process of ion migration. If you insist on using a hand whisk, you will probably find a difference. With that said, I would add the following. Copper bowls are EXPENSIVE and hard to maintain. Instead of a $100 copper bowl dedicated to making only egg foam, I would invest $10 in a hand held mixer that I could use with my stainless steel bowls instead.
Session C. Green Boiled Eggs
That is the first problem. Eggs in the shell should NEVER be boiled! The simmer stage is quite enough, and they should be finished steeping in the hot water until the proper amount of time elapses. I will not be so presumptive to know how you like your eggs cooked, but from soft cooked to hard cooked the method is the same, only the time in the hot water is different.
You have to understand some basic biology here. Remember that an egg is the spaceship that an embryonic bird occupies, and it has to supply EVERYTHING, except air (eggs are porous, so oxygen can infiltrate, but commercial ones are usually treated to plug the pores so that they keep fresh longer), that the little bird to come needs. That means proteins, and lots of them. It also means water, and iron to form new red blood corpuscles.
Just as in the last piece, many of those proteins contain sulfur. When overcooked, boiled eggs denature proteins and release hydrogen sulfide, a toxic gas that smells like rot. Rotten eggs are full of it, but hardly anyone sees them anymore. It turns out that the white of the egg has lots of sulfur in it, and the yolk has lots of iron. When iron and sulfur react, harmless but unattractive iron(II) sulfide forms, at the interface of the iron rich yolk and the sulfur rich albumen. To prevent this, do as I said about simmering and holding time, then immediately when the time elapses pour off the cooking water and flood the vessel with cold tap water. Keep the tap water running, slowly, until you cannot tell much difference betwixt the incoming and outgoing temperature, then cut it off, pour out some of the water in the vessel, and add ice. Since I have been following this procedure, I have never had a green yolk nor a tough egg.
Session D. Brown French Fries
Baking prepared French fries give you nothing like a good French fry. To make a good fry, you have to use fresh potatoes. The russets seem to make better ones than red potatoes do, and that has to do with the nature of the molecular structure of the starch in them.
To make good French fries, take your potatoes and slice them into whatever thickness that you prefer. Be sure and slice them into a bowl of heavily salted water to keep them from going brown, and also to draw some water from them. Then put them aside for a while. If you like to peel them, that is fine. If you prefer to keep on the peels, just scrub them well.
Take your deep fryer or skillet, and heat up some oil or fat. Beef tallow is by far the best frying oil for potatoes. It also gives a flavor like nothing else. McDonald's used it for a long time, but has been forced to use other fats these days. Soy oil or canola are OK, and some folks rave about peanut oil.
Heat up enough oil to cover the potatoes. NEVER crowd them in whatever cooker that you use. As the oil heats, dry off the potatoes (a salad spinner works well, but clean kitchen towels are fine, and can be reused). Once your oil is at about 182 ºC, add some of the potatoes, and cook until they are just light brown. Take them out and put more in until all of them are ready.
Now, and this the McDonalds trick, refrigerate the partially cooked ones until they are quite cold. You can freeze them if you want. Now, take these cold and aged partially cooked fries and put them into fat at around 190 ºC, and cook until they look brown. Drain them on newspaper on a flat pan covered with clean paper towels or, cheaper, opened napkins. Before they cool, salt them with regular iodized salt that you have ground in a mortar and pestle.
The chemistry is not really understood, but my thought is that very fresh oil does not contain catalytic agents that accelerate the browning reactions. This has not been studied very much, but from empirical evidence it is known that oil that has been used a time or two previously makes more nicely browned French fries. It also tends to keep burnt remnants that have broken off the potatoes, and thus makes new ones sort of bitter. Here is the resolution.
Use a coffee filter and a strainer, and pour the still hot oil into the filter. Let it stand overnight and after one or two frying events you will have oil that will brown the French fries properly. As it gets bad, replace it with new oil (keeping at least 25% of the old) and almost as by magic you will always get tasty, well browned French fries.