Hello, everyone! Tonight we shall look at some of the chemistry that occurs when you cook. Cooking is essentially a chemical process, and the change in chemical properties in the materials changes the physical nature of them.
We shall talk a bit about biology as well, because of the possibility of food poisoning and other biologically mediated afflictions. I promise to be non disgusting with it.
I have chosen six topics, and interestingly a couple of weeks ago here two of them were mentioned either in the main text or in the comments. In no particular order, here we go.
Sweet sweet potatoes
Sweet potatoes are one of my favorite vegetables. I love them baked, boilt (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 are acutally morning glories with an edible tuber (see my previous installment of Pique the Geek from Sunday past for a full treatment). Most of the energy is stored 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, being almost inactive at room temperature and completely denatured. This enzyme starts becoming active at about 135 degrees F, and is destroyed at around 170 degrees F. This has serious cooking implications.
"Regular" potatoes are usually baked at around 400 degrees F, or boilt at 212 degrees F (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 170 degrees F 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 170 degree F 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 400 degrees F until it is soft. I know that I said that the enzyme is denatured at 170 degrees F, 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 150 degrees F. Then add your sweet potatoes and hold the temperature there for half an hour. Since water transfers heat much more efficiently than does 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. Temperatures below around 55 degrees F can cause a condition called "hard heart", rendering the center uncookable. I know not of any studies on the condition, but my speculation is that either the cold temperatures either ruined the enzyme (which I find unlikely), or that some conversion to starch to cellulose has occurred, more likely based on the evidence. You can cook cellulose all day and not soften it. Try boiling cotton balls and see how they change.
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. They will corrode unless you immediately after use wash and DRY them, and the corrosion products are much more soluble than the metal itself. Instead of a $50 to $100 copper bowl, dedicated to making only egg white foam, I would invest $10 in a hand held mixer that I could use with my glass and stainless steel bowls instead.
Green Boilt Eggs
That is the first problem. Eggs in the shell should NEVER be boilt! 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, boilt 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 any more. 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 can not 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.
Before I learnt this technique, I often had green yolks (and rather tough ones as well). Since I have been following this procedure, I have never had a green yolk nor a tough egg. Depending on your altitude, the times will vary (longer the higher the altitude), so you may want to do a couple of experiments to find the exact times for where you live. At altitudes of over 5000 feet, you might want to use a bit faster cooking method than a simmer, but a full boil is still too fast.
Rare Pork
OK, not really rare, but not overcooked. Forever we have been told to cook all pork products to the well done stage (around 185 degrees F). This was based on the fear of trichinosis, an infection that can be quite dire caused by a parasitic worm found in pork and its relatives. As a matter of fact, the parasite is killed at about 137 degrees F, so the 185 degree target was always overkill. But pork has changed. In the past 30 years, pork has become very lean. 2011 pork is, depending on the cut (except for bacon) contains from 20% to 50% of the fat that 1980 pork did. But cooking methods have not been updated.
For meat in general, fat content is associated with tenderness. Thus, Prime beef has a lot of fat (the so called marbling) than Choice, and Choice more than Select. Try to find Prime grade outside of an upscale restaurant! Pork has no such grading system, but modern pork would grade to Select or even less. Back when pork was very fatty, it was quite forgiving to being overcooked. This is not the case any longer. If modern pork is overcooked, it WILL be tough and dry.
Try cooking pork this way (by the way, this applies only to SOLID pieces, not ground pork. Any ground meat needs to be cooked to near the well done stage because of bacterial concerns, but there IS a trick to allow for safe, but rare, hamburgers and other ground products). Let us take, say a Boston butt, acutally shoulder. Rinse the meat well in cold water (to knock down surface bacteria count) and coat it with vegetable oil. This adds only a trivial amount of fat. Then season the surface with salt (I like to use Kosher salt so that I can see where I put it), pepper, and freshly ground black pepper. If you like, take a very sharp, small bladed knife and punch little pockets in which you can insert slivers of fresh garlic cloves. I also like to sprinkle some ground dry mustard on the surface.
Put it, fat side up (if there is any fat on it) onto a pan and place in a 450 degree preheated oven. Let it stay there for about 45 minutes (assuming a four or five pound roast), then turn down the temperature to 325 degrees. After another half hour, use a calibrated meat thermometer to check the internal temperature. When it gets to 135 degrees, take out the roast and plate it (put it on a serving plate, cover with foil, insulate the foil with a clean kitchen cloth) for ten or 15 minutes (depending on how big it is), then carve it. You will find a succulent, juicy piece of meat that is delicious, and nothing at all like the 185 degree ones to which you are accustomed, and just as safe.
By the way, pork in the United States (I can not speak for other countries) is so safe that only fewer than a dozen cases of trichinosis have been reported over the last decade. We can thank USDA regulations and inspection for that, so if you really want truly rare pork, the danger is nil.
Certain wild game is prone to that parasite, in particular bear (a close relative to hogs). I would recommend cooking porcine game to at least 150 degrees for safety reasons, but there is a workaround IF you love your bear rare (cool, a rhyme!). It turns out that the parasite is killed by being frozen at 5 degrees F or lower for three weeks or more. That eliminates any danger from the parasite.
I recommend the high (450 degrees F) initial temperature to assure that any surface bacteria are killed, and also to assure some good browning my the Maillaird reactions. If you do not bard or coat in oil the piece, modern pork does not have enough fat to react with the proteins to cause a nice, tasty, brown crust.
Safer rare Hamburgers
I really do not like overcooked meat. Ma (my grandmum) would cook meat to death, and it was always dry and tasteless. However, ground meat presents a hazard of bacterial toxins and all store ground meat (unless it is irradiated with gamma rays) should be cooked to the well done (Ugh!) stage. Here is the workaround that I mentioned previously.
Buy a meat grinder, first. Keep it as clean as possible, second. That is not as easy as it sounds, but is critical. Then buy whatever leanness of meat that you want for your hamburgers. I like the 73/27 for commercial ground beef, but doing it this way allows you to use leaner cuts, like chuck or even round (a bit too lean for my taste). Do not cut off any fat. Thicker pieces work better than thinner ones for this process. Remember, bacteria do NOT penetrate into the interior of meat, unless the carcass itself was diseased. Take a vessel of water and bring it to the boil. Then take the (refrigerated, or even frozen) piece of meat and immerse it into the boiling water for about a minute.
This kills all of the bacteria on the surface, and washes away any toxins that they might have produced. Now take the meat and run it through your grinder, twice if you want something that is more like commercial hamburger meat. Only the first couple of millimeters of meat is cooked (less if you use frozen meat), so when you grind it into hamburger meat, very little cooked material is inside of the bulk of the meat. You can cook very rare hamburgers from this meat without having to worry about bacterial food infections, since the outside that is ground into the inside is essentially sterile. That is not the case for commercial hamburger, where raw meat is ground.
Brown French Fries
First of all, 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. I like shoestring ones, when I eat French fries maybe four times a year, but many folks like thicker ones. Anyway, 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, but it is sort of hard to find now. 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.
As an aside, most people with peanut allergies do fine with peanut oil. The allergenic material is a protein, and is not oil soluble. On occasion enough of the protein DOES pass into the oil to cause problems, but this is rare. I do not use peanut oil because I find soy and canola to do fine, and they are cheaper than 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 360 degrees F, 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 375 degrees F, and cook until they look brown. Use a slotted spoon and 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 (or take the packs of very fine salt that McDonalds uses). But they are not golden, but are done! Doc, what is wrong?
The chemistry is not really understood, but my thought is that very fresh oil it "too intact", in that it 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.
Buy a cheap pack of coffee filters and a strainer large enough to hold them, 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.
This is sometimes called the Belgian method of making French fries, but it WORKS, and well. Now, for the finale, what about those hollow ones?
Hollow French Fries
Treat the potatoes and oil just as above, but cut the potatoes into inch wide and 1/4 quarter thick ones, give or take a little. Precook them just as before, at 350 degrees, and put them in the cold for an hour. Now, heat the fat up to 400 degrees, and put them, only a few at a time, into the hot oil. They will cook fast, so do not take your eyes away. If all goes well, they will start to swell from the inside (the crust has made a steamproof barrier) and puff into a hollow, thick fry.
Salt and serve immediately! Do not cover them, because the steam will make them flaccid. These are more like a novelty, but they are great for scooping dips, and if you make them successfully, you will be the talk of the cooks! They are best served with two or three for each person, no more, or they will become cold and unattractive.
Well, that is about it. Please let us know about your kitchen tricks. By the way, dinner for me is just the kind feedback from this wonderful readership. I am not sure about the topic for Sunday for Pique the Geek, but am leaning towards the element Hydrogen, the basic building block of everything. If anyone has a better idea, please serve it as a comment.
Warmest regards,
Doc