Friday, February 4, 2011

Oven Tests


Even with just a casual reading of this blog, it could hardly go unnoticed that I am consistently cooking the loaves for less time than Hamelman calls for. Why is this?

One obvious answer is that my oven is simply too hot. There are several simple ways for the home cook to determine if an oven is running hot or cold without calling in a professional to have the oven recalibrated. The simplest approach is to use an oven thermometer. Based on recommendations from Cook's Illustrated, I've used a top rated thermometer to check the temperature of my oven. In fact, the thermometer showed my oven to be running about 30 degrees too low, just the opposite of what I would expect. Of course, the thermometer could be wrong.

Thermometers can be check by placing them in an ice slurry for 32 degrees (be sure the slurry is at equilibrium) or boiling water 212 degrees (minus 0.9 degree for every 500 feet above sea level). While a great test for your Thermapen, neither of these are very useful for an oven thermometer.

Fortunately, there's another simple test that is reliable if done carefully. Sugar is known to melt at 367 degrees. This simple observation can be used to confirm that behavior of an oven. Simply preheat the oven to say 365 degrees and then place a small bowl of sugar in the oven and leave it for a while (at least 30 minutes). It shouldn't melt although it may discolor. Note, it is extremely important to let the oven stabilize before you put the sugar into the oven since most ovens will initially oscillate around the target temperature. The oven coils should not be glowing, and you should put the sugar into the oven quickly keeping the door open for as short a time as possible.

Next remove the sugar, reset the oven to 370 degrees. After the oven has stabilized, you can return the sugar to the oven. After a bit it should melt. Be patient, this can take a half-hour or more.

If your oven is running hot, then it will melt at a lower temperature. If your oven is running cold, you will need a higher setting before the sugar
melts.

Using this approach I found the sugar would not melt in my oven when set at 380 degrees but would melt at 385 degrees. Thus, my oven is running about 15 degrees lower that where it is set. This isn't quite as bad as the thermometer indicated, but I trust the sugar more. (This method is describe in Cooking for Geeks, a interesting but very, very uneven book.)

Temperature only give a part of the picture. Items in an oven heat by several mechanism (induction, convection, and induction). If there is better air circulation, then an item will heat more quickly than the temperature would indicate (as in a convection oven).

Cook's Illustrated (January 2008) has another test that can give an idea about this. The idea is to allow the oven to stabilize at 350 degrees (I used 365). Take a two cup Pyrex measuring cup with one cup of water at exactly 70 degrees. Quickly put the measuring cup into the oven and leave it there for 15 minutes. For a normal, correctly calibrated oven, the temperature should rise to 150 degree over that time. In my oven, it went to 148 degrees, pretty close.

(There is one other test from Cook's Illustrated that is used to test broiler evenness. The idea is to put in a sheet pan and toast it. This will show hot spots. While I was at it, I ran this test as well.)

So, oven temperature doesn't seem to be the problem. There are several possibilities, but I have no definite answer at this time. Perhaps the dough has risen quite enough. Perhaps, it is too warm to begin with. Or perhaps there are some issues with Hamelman's recipe. I'll continue looking for a solution, but this really isn't a big issue with me. Basically, I'll just keep using my Thermapen to check the bread removing it when it is done. In the meantime, I'll keep setting the oven to the temperature specified by Hamelman without making any corrections in my oven. This is what I've been doing in the past, and it would only create confusion to change now.

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