June 19th, 2012
Gah! I hate them!
They seem remarkably handy because you can see through them, but they are an enemy to be destroyed.
Take a look at your glass pot lid. Notice it has a little metal ring in it, with a hole or valve through the center? The reason that hole is there is not because there’s a nascent piercing trend in cookware. No, it’s there for a bad reason. Marketing will tell you that it allows some pressure to be relieved and thus reducing rattling of the lid. That is true. It isn’t however the reason that only glass (and not metal) lids have this feature. It’s there to give the glass some protection from thermal shock and stresses.
In other words, it’s allowing heat and steam to escape and has a negative effect on the cooking of your food. Wonderful, huh? Want to know the hows and whys?
Glass is a better thermal insulator than steel. In that, it is better at keeping heat inside (our outside) of something. But because that hole is required, it’s like leaving a window open in mid winter in a well-insulated house. It’s counter intuitive, slows down your cooking and creates uneven temperatures within a lidded pot.
This makes stovetop cooking and steaming of food, or lidding a pot off the heat far less efficient. In fact, it kind of defies the purpose, donchathink?
By far, the worst offenders are dutch ovens with glass lids.
As an aside to fill you with a little shame, one credible story says the “Dutch” in “dutch oven” comes from an old ethnic slur against the Netherlanders meaning “fake” or “cheap”, i.e.; “going Dutch”. In Europe, they’re generally referred to as casseroles or cocottes. If you own a dutch oven, I bet you feel a little dirty now, don’t you?
The dutch oven was designed that its lid was generally heavy and very heat conductive, so that when put into a wood or brick oven or hung over a fire, would cook its contents from all sides. Oftentimes, hot coals would be placed on the lid of a dutch oven to facilitate heating, which is why several brands like Staub and many models of Lodge have a lipped lid. In other words, it acted as an oven within a larger oven. Heavy cast iron or enamelled cast iron dutch ovens are preferred because they have a high thermal retention and inertia. Because of its heavy, tight fitting lid, a small amount of steam pressure will build up inside, keeping things moist as well as increasing the thermal conductivity of the air trapped in the vessel itself. Consider it a very very low PSI pressure cooker.
With glass being a great insulator, the advantage of cooking from all sides when in an oven goes straight out the window, and the vented lid does nothing to keep that small amount of pressure in. If your oven is able to use both upper and lower elements at the same time, it’s even more of a waste, as much of that thermal energy from above would be spent trying to heat the glass, rather than being passed into the dutch oven.
The moral of the story: When buying kitchen gear, always remember that physics wins out over “convenient features”. Glass lids seem like a smart idea, but they give a false sense of security and take away many of the advantages of lids were created for.
And seriously, once splattering and critical mass of condensation is taken into consideration, exactly how much can you see through those glass lids anyway?