A recent trend in cookware has involved increased popularity of pots and pans that are sometimes called "ceramic," sometimes called "glass-ceramic," and sometimes called "enameled porcelain." These terms don't always mean the same thing! We would like to tell you more about these terms and about the nature and safety of this cookware.
For many years, "ceramic" simply meant "made of clay." Ceramic cookware was cookware made from various types of clay, various types of soil featuring special mixtures of minerals and elements.
Unglazed clay pots are often still made in this way (from the clay alone). They can make great cookware, provided that the clay is high quality (not contaminated, for example, with unwanted elements like arsenic).
It is also important that unglazed clay pots are fired properly during their manufacturing. One of the important reasons for this is that clays typically contain both aluminum and silicon, elements that are capable of causing health problems when free to migrate from a clay pot into food. But when clay pots are fired properly, a very inert, durable material is formed (through a process called vitrification) and the aluminum and silicon get bonded together into the pot's structure. They are then no longer free to pass into food.
Please note that not all clay pots (also sometimes referred to as earthenware pots or terra cotta pots) are intended for stovetop cooking owing to temperature sensitivity. Additionally, they will typically crack if they undergo dramatic changes in temperature (for example, being taken from the refrigerator directly into a pre-heated oven).
You will also find many clay pots that have been glazed. Glazes usually consist of glass-like substances that are safe for food contact.
Yet, care does need to be taken when choosing glazed clay pots as there are some materials you will want to avoid. These include the heavy metals lead and cadmium that are sometimes ingredients in glazes. In addition, you will want to avoid certain types of potentially toxic color pigments that are used to color the glaze. Sometimes you will be able to tell that a color pigment is potentially toxic from the name of the pigment itself (like cadmium red or cadmium orange) but most of the time you won't be able to do so. For this reason, we recommend purchase of glazed clay pots from a reputable source that specifically states the absence of potentially toxic, synthetic pigments (as well as heavy metals) in the glazing of the pot.
Today, most cookware that is called "ceramic" no longer consists of clay. The making of ceramic cookware more often begins with the making of glass. There are many different kinds of glass, but most involve a combination of naturally occurring earth materials (including sand, gypsum, soda ash, limestone, and dolomite). Many different minerals are present in this mixture, including calcium, magnesium, sulfur, sodium, carbon, and silicon. Like the aluminum and silicon found in clay, the silicon found in glass might create a health risk for use of glass in cookware were it not for the high-heat manufacturing process that vitrifies the glass. At high heats—for example, 3,000°F (1,649°C)—a stable structure is formed that leaves the silicon bound to other elements and makes the glass safe for food contact.
In the manufacture of ceramic cookware, a second step must take place after this initial creation of glass. Once the glass is formed and cooled, it gets reheated to initiate a process called partial crystallization. This partial crystallization process is what transforms the glass into a ceramic. Chromium, zinc, and titanium are examples of elements that might be added to the reheated glass in order to help control this partial crystallization process. But these elements get solidly bound into the structure of the ceramic and are stable in the material rather than left free to migrate into food. The partial crystallization of ceramic cookware typically makes it far less porous than clay cookware, and also higher in strength. One of the best-known glass-ceramic lines of cookware products in the U.S. is Corning Ware (TM).
Porcelain is another type of ceramic material that's closely related to both clay and glass ceramic. In fact, porcelain often contains kaolinite clay and may also contain glass or glass components, as well as other materials like feldspar or alabaster. Porcelain is fired at high temperatures like clay and glass ceramics, and like those materials, it may be glazed or unglazed.
Porcelain enamel cookware is made by taking porcelain and melting it onto another metal like cast iron, aluminum, or stainless steel. The process used to fuse the two materials together turns the porcelain into an integral component of the cookware rather than merely a "coating." Porcelain enamel covered aluminum and stainless steel cookware is not as heavy as porcelain enamel covered cast iron, but some people may prefer the "hefty" feel of a porcelain-enameled cast iron. All types of porcelain-enameled cookware can provide safe food contact surfaces provided that the porcelain enamel is not chipped or cracked. (If the porcelain enamel surface is chipped or cracked, whatever material lies below the porcelain coating—for example, aluminum or cast iron—may be able to migrate into the food in small amounts.) For environmental reasons, some people prefer not to make use of aluminum cookware in any way, even though porcelain-covered aluminum prevents direct contact between the aluminum and the food from a health standpoint. Due to environmental issues involved with the commercial mining of iron ore, some people also prefer not to make use of cast iron cookware, whether covered with porcelain enamel or not.
Along with stainless steel, glass, Pyrex (TM), and cast iron, we like this ceramic family of cookware products for use in a healthy WHFoods kitchen. By contrast, we do not recommend use of any synthetic non-stick surfaces - including Teflon (TM)—that include PTFE (polytetrafluoroethylene) in their composition; any aluminum pots and pans (including anodized aluminum); and any cooking plastics (for example, microwavable plastic containers).
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