More and more, I'm seeing kitchen gadgets such as spatulas and pastry brushes made of silicone. What amazes me are the baking pans and muffin "tins," which look and feel like rubber, but can supposedly stand oven temperatures up to 500 degrees. What's the secret?
That which we call rubber by any other name would not smell as sweet.
Or, in less poetic language, all rubber is divided into three parts.
Sorry. I'll try again. There are three basic kinds of rubber: natural rubber, which comes from latex, the sap of the tropical tree Hevea brasiliensis; synthetic rubber, which comes from a chemical plant; and silicone rubber, which comes from, well, a different chemical plant.
The last two were dreamed up by chemists to duplicate some of natural rubber's unique properties and improve upon others. A synthetic rubber called neoprene was first marketed by DuPont in 1931, while a wide variety of silicone rubbers have been manufactured by General Electric and Dow Corning since the 1940s. These two man-made products inherited the silly name "rubber" from the natural material, which was so-christened by the English chemist and clergyman Joseph Priestley in 1770, when he found that it would rub out pencil marks.
Unfortunately, in recent times the word "silicone" has been implanted, so to speak, in the public's mind in but a single context: cosmetic augmentation. But silicones are a remarkably versatile family of chemical compounds with hundreds of uses. In culinary applications, the French fiberglass-reinforced silicone baking-pan liner called Silpat has been used in professional kitchens since it was introduced in 1982. But silicones have only recently invaded the American home kitchen in many forms, all approved by the Food and Drug Administration for repeated contact with food. Today, the whole baking pan, not just its liner, is made of silicone.
Before I go any further, I must straighten out some terminology, because the words silicone and silicon are so often mistakenly interchanged.
Silicon (no e) is a chemical element, the second most abundant element on Earth (after oxygen). A rock-hard, brittle material, it would make the world's worst cake pans, not to mention surgical implants. However, silicon the element is a semiconductor and therefore immensely valuable in the form of "chips" or microprocessors in computers and hundreds of other electronic devices. That's why the high-tech region around San Jose, Calif., is called Silicon Valley. (It is to be carefully distinguished from Los Angeles, which has been dubbed Silicone Valley for reasons that I need not explain.)
Silicones, on the other hand, are chemical compounds that, like the natural and synthetic rubbers, are polymers, meaning that their molecules consist of long chains made up of thousands of smaller molecules tied together. Silicone molecules have spines made up of alternating atoms of silicon and oxygen, to which are attached various groups of carbon and hydrogen atoms. Depending on the lengths of the chains and the natures of the attached groups, silicones can range from liquids (used in brake fluids and water-repellent sprays) to gels (in breast implants) to greases (in lubricants and lipsticks), and elastomers or rubber-like materials (in Silly Putty, Superballs, refrigerator door gaskets and, now, kitchenware).
Silicone bakeware has a remarkably useful set of properties. First, the material is inherently translucent, so a veritable kaleidoscope of bright colors can be incorporated into the products. (KitchenAid's line of muffin pans, loaf pans and cake pans comes in red or blue.) They can withstand high temperatures without melting (i.e., without their molecules flowing apart from one another) because the molecules are very long and tightly intertwined, like a cold, leftover plate of Spaghetti with Glue Sauce. That's also why you can take them directly from the oven to the freezer or vice versa without any fear of cracking; the molecules, while individually flexible, are so rigidly fixed in place that the material can't expand or contract very much with changes in temperature.
Silicones don't absorb microwaves, but like all microwave-safe utensils they can get hot in the microwave oven from contact with the heated food. Because silicones are chemically inert, the pans are dishwasher safe; caustic detergents can't touch them. Also because of their nonreactivity, they are more or less nonstick; cakes and muffins release easily -- most of the time -- since you can flex the pans to pop them out. But don't try to use them as Jell-O or aspic molds; sitting the mold in a warm-water bath won't release the gelatin because the silicone is a heat insulator.
Any disadvantages? Being electrical insulators (one of the most important properties of silicone rubbers in many other applications), they are subject to static electricity and may collect dust in the pantry between uses. And their floppiness can be disquieting, for example, when carrying a batter-filled pan to the oven. Carry it on a rimless baking sheet, using the sheet as a peel when inserting the pan into the oven.
Caveat emptor department: As with everything else, there are high and low qualities of silicone bakeware. Remember that "silicone" isn't a single chemical material. Dow Corning, for example, sells dozens of different silicone formulations with different properties, for fabricators to use in molding their commercial products. Some may not be as heat-resistant as others, so check the maximum temperature ratings on the labels. They can range from 450 degrees up to 675 degrees for the silicone trivet pads.
Labelingo: Perspicacious reader David A. Kravitz of Fairfax reports that on the bottom of a package of Stash Premium Chai Spice Black Tea it recommends that it is "Best consumed by 06/18/2006 09:37" . . . . And then get out of the way quick?
(Have you noticed any silly things on food labels? Send your Labelingo contributions, along with your name and town, to Food 101, Food Section, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or to the e-mail address below.)
Robert L. Wolke (www.professorscience.com) is professor emeritus of chemistry at the University of Pittsburgh and the author, most recently, of "What Einstein Told His Cook: Kitchen Science Explained" (W.W. Norton, $25.95). He can be reached at email@example.com.