In baking especially, which material you use can have a significant impact on the results. Ask just about any serious or professional baker whether they prefer glass or metal, and the answer is almost always steer, well, clear of glass.
Simply put, says pastry chef and cookbook author Lauren Chattman, “It’s terrible for baking.”
“We avoid glass at all costs in a professional kitchen,” says Joanne Chang, cookbook author and chef behind the Boston-area Flour Bakery + Cafe.
Still, manufacturers consistently offer loaf pans and square and rectangular baking dishes in glass. And, as Chang points out, recipes often specify the size — not material — of a pan or dish (there is a not necessarily universal implication that pan means metal and dish glass or stoneware). Here’s what you need to know about the differences and how to pick the right vessel for the right bake.
Their heating properties. Glass is not a great conductor of heat, Chang says. “It takes a long time to heat up.” And once hot, it retains the heat and takes longer to cool down. (Ceramic is similarly a better insulator than conductor. Silicone also transfers heat slowly.)
Glass is fine for dishes that bake for a long time without much danger of overcooking, where a crust around the edge is not a bad thing, according to David Joachim, Andrew Schloss and A. Philip Handel in “The Science of Good Food.” Examples: casseroles, large souffles and pies.
Metal is a much more efficient conductor, with some types of pans preferable to others. “Heavy-gauge aluminum is the best choice for all-purpose baking pans. It transfers heat quickly and doesn’t warp or have hot spots like less expensive thin-gauge pans,” according to “The Science of Good Food.”
Other characteristics to consider. Glass’s ability to break is “a huge liability in the kitchen,” says Chang, whether in a busy professional bakery or your home. It shouldn’t be placed under the broiler because that intense heat can cause it to shatter. This can come into play with some pie or casserole toppings. Glass bakeware tends to be heavier than metal, which can affect maneuverability and the ease with which you turn a cake out when finished.
Assuming you manage to avoid breaking it, however, glass is durable — resistant to scratches and dings from serving utensils. And it won’t react with acidic ingredients the way some metal pans can, causing off-flavors in food or discoloring on the pan.
Metal won’t crack when you drop it, though it can be scratched by sharp tools. Washing and promptly drying metal pans is especially important for those that haven’t been treated to resist rust. Some pans can oxidize or discolor in the dishwasher, which is why I always prefer to clean them in the sink.
Look for light-colored, dull pans — too dark and they’ll absorb too much heat, leading to overcooking; too shiny and they won’t absorb enough heat.
I favor anodized aluminum round cake pans, such as Fat Daddio’s, which are treated to prevent reactions with acidic ingredients and won’t rust. I also have a number of aluminized steel loaf and square pans from USA Pan that combine the conductive power of aluminum with the durability and heft of steel, as well as a silicone coating for easy release. Chattman likes the Goldtouch line from Williams-Sonoma.
Glass does have a distinct disadvantage over metal when it comes to shape for baked goods. The edges of glass pans are sloped and rounded, meaning it’s impossible to get attractive sharp corners and straight edges. As Susan Reid at King Arthur Baking writes, “Glass pans’ dimensions can be all over the place (try taking a measuring tape to the store next time you shop; you might be surprised).” Metal pans tend to be more uniform, which helps ensure recipe success.
Which to use when. “Cakes should definitely go in metal,” Chang says. As you can see in the photo, the slower transfer of heat to the batter means cakes baked in glass (or ceramic) will take longer to cook than those in metal (5 to 8 minutes longer, according to a test with yellow cake done by Cook’s Illustrated).
Those two coffee cakes were baked for the same amount of time, but the center in the glass pan was underdone, leading it to sink after it was pulled from the oven. So why not just leave it in the oven longer? The issue is that the longer a cake, or even a batch of brownies or blondies, bakes, the more likely the edges will be overcooked — and disproportionately higher up the pan — by the time the center is done. They may continue to dry out as the pan cools, too.
The answer on pies is less straightforward, as you’ll find advocates for both metal and glass plates. In “The Book on Pie,” Erin Jeanne McDowell says that what glass lacks in conductivity compared to metal or stoneware (her favorite option), it makes up for in transparency. That is, you can see exactly how brown the crust is. Placing a glass pie plate on a baking steel or baking stone can improve browning and crisping, too. Metal pans conduct heat better and are generally thinner than glass, boosting their ability to conduct and distribute heat, McDowell says. Beginners may find it helpful to start with glass and then graduate to metal or ceramic as they gain confidence.
For more rustic desserts where shape doesn’t matter, glass, as well as ceramic, can be an acceptable option. Think cobblers, crumbles and crisps. Here, the rounded edges can be an advantage for scooping up more liquidy dishes. Much like the edge of a cake, though, you do run the risk of scorching the bottom of a sugary fruit filling, Chattman says, so keep an eye on it and err on the side of caution. The filling may continue to cook as it rests in the dish. That also means you’ll be able to pull it out of the oven before dinner and still have it warm when you’re ready to serve dessert, Chang says.
Curious about silicone? I find it too flimsy and floppy for anything substantial, such as lots of cake batter. Chattman says that you won’t get desirable browning either. In “The Baking Bible,” Rose Levy Beranbaum notes that silicone’s poor conductivity can lengthen baking time. She says she prefers to use it in situations where you’re placing something in a water bath or in smaller molds, such as muffins or cupcakes, which cook faster anyway.
How to adjust. Glass dishes and metal pans are on the more affordable side of kitchenware, and are often fairly comparable in price. Still, whether limited by budget, space or circumstances (i.e. baking somewhere other than home), there are times when you won’t have the pan you want or need.
To try to even out the disparate heat between the edges and center of foods baked in glass, try dropping the oven temperature by 25 degrees and baking longer. A longer bake time might cause the top to brown quicker, in which case you can loosely tent it with foil.
For bars, Chattman says you can even slightly underbake them, which is what she prefers anyway, to account for the residual heat after baking. Chattman says the typical uneven heat of ovens can exacerbate the effects of glass bakeware, so be sure to periodically rotate the dish to combat hot spots.