When You're Hot, You're Hot -- Or Not

By Robert L. Wolke
Sunday, November 19, 2006

Of all the vital questions facing our nation in these post- election weeks, the most vexing may be, "How do I know when my turkey is done?"

This would seem to be a simple question to answer, because almost every food publication in the country is referring its readers this week to a chart showing that if your turkey weighs X pounds it should be done after Y hours in a Z-degree oven. (The Post sends people to the one at http://www.fsis.usda.gov/Fact_Sheets/Lets_Talk_Turkey/index.asp.)

The label on the turkey tells you the value of X, and your clock tells you the value of Y, but nobody ever questions the value of Z. We blithely set our ovens for a certain temperature and figure that's the temperature we will get. But shouldn't we be a bit more agnostic, as scientists are when taking measurements? When you set your oven for, say, 325 degrees, does it really heat up to 325 degrees?

I know you're already anxious about your turkey and don't need anything new to worry about. Well, I never worried about the Z factor either until a few weeks ago, when my wife was baking pumpkin pies. The pies just wouldn't cook in the expected amount of time; their crusts remained soft and the custard hadn't firmed up. Thinking there might be a glitch in the recipe, she made another batch, with the same result. That's when she called in the sage of all things chemical or physical, the solver of all problems (me).

"Let's check the oven temperature," I said.

I set the oven for several different temperatures, allowing time for it to reach each one, and measured them with an oven thermometer. (Those cheap little metallic ones that you hang on the oven rack are just fine, and you have plenty of time to buy one before the Big Day.) My actual oven temperatures averaged 22 degrees lower than their settings. I wondered why.

Summoning my finely honed powers of scientific observation, I noticed that there was a 14-by-16-inch slab of stone resting on the bottom shelf of the oven. It was our baking stone, also known as a pizza stone, which we leave in the oven after using it because it's just too darned heavy to be schlepped in and out.

"Aha!" I said ("eureka" having been vastly overused). "The stone is casting an infrared shadow."

"Huh?" my wife inquired.

"You see, electric elements heat the oven mainly by infrared radiation, which travels in straight lines. That slab of stone is shielding the middle of the oven from the heating element at the bottom and preventing it from reaching the set temperature."

"Yeah, right," she said. "Just fix it, okay?"

I removed the stone and tested the temperatures again, and all the Z's were right on the button.

You say you have no baking stone, yet your oven still doesn't get as hot as the set temperature? There's another possibility: It could well be the gasket around the oven door. If it no longer makes a tight seal, a surprising amount of heat can leak out, and the thermostat might not be able to keep up. I've had experience with this problem, also. My 10-year-old gasket had stiffened to the point where it wasn't conforming snugly to the mouth of the oven. I could even feel the heat leaking out of the top edge. I obtained and installed a new gasket, and the temperatures were once again where they belonged.

You can order a door gasket from the oven manufacturer or search for "oven door gasket" or "appliance parts" on the Internet. You probably can't get one in time for Thanksgiving. Never fear, however. Test the oven as above and raise the setting as necessary, no matter what may be the cause.

Oh, and don't forget to clean your oven after the holiday is over. Turkeys in roasting pans can make quite a mess. Don't let your guests peek inside.

With many manufacturers trying to remove trans fats from their processed foods, I am seeing an increase in the use of palm, palm fruit and palm kernel oils. Are any of those good for you? My understanding is that palm kernel oil is one of the highest in saturated fats. Is there an allowable daily limit in saturated fat intake?

The answer to your last question is yes. The USDA's allowable "daily value" for saturated fats is 20 grams.

Indeed, food manufacturers and fast-food chains are scrambling to eliminate partially hydrogenated oils from their products because partial hydrogenation -- forcing hydrogen atoms into unsaturated spaces in the fat molecules -- produces trans-fatty acids, which have been associated with elevated "bad" cholesterol and risk of heart disease.

Enter the so-called tropical oils, all of which are highly saturated (92 percent for coconut oil, 82 percent for palm kernel, 50 percent for palm). Food manufacturers are using those oils to increase the saturation level and improve the solidity and stability of their products without having to hydrogenate less-saturated vegetable oils.

Tropical oils are the pawns in a great battle that has been raging in recent years. On one side are the producers, mainly in Malaysia and Indonesia (palm kernel) and the Philippines (coconut), and their acolytes, many of whom fervently trumpet the alleged healthfulness of coconut oil. (Recent research has indicated that certain fatty acids in palm and coconut oils may actually be beneficial to health.) On the other side are those who adhere to the conventional wisdom that all saturated fats are harmful.

I shall not join the fray, because on this issue the saturated-fat lady has not yet sung. Whether the substitution of tropical oils for hydrogenated vegetable oils will lead to a net health benefit remains to be seen.

Robert L. Wolke (www.robertwolke.com) is professor emeritus of chemistry at the University of Pittsburgh. He can be reached at wolke@pitt.edu.