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Culinary Lesson #14 - Knowing Your Oven

Saturday, January 19, 2013

How many of you don't have the best of luck with the baking times that recipes call for?  Whether this means  cookies that take 20 minutes to bake rather than 12 minutes, or brownies that burn before the baking time is even half up, most of us have experienced some sort of oven frustration before.  Sure, the problem could be the fact that you forgot an ingredient, which in turn threw off the whole baking process.  But if you always seem to experience that your foods take longer than called for or finish baking faster than expected, you can (most likely) put the blame on your oven.

Image from vermontkitchensupply.com.
One of the first things I made after moving into my current apartment this past summer was a batch of chocolate chip cookies.  I set the mental timer to 10-12 minutes, and after the time had passed, I returned to check on the cookies only to find blobs of melted cookie dough.  In the end, they turned out fine, but I had to essentially double the standard baking time that was called for.

After accepting the fact that my oven clearly didn't meet the temperatures I had input, I had two options for future baking experiences.  First, I could continue to set the oven to the temperature stated in the recipe and then accept the fact that I wouldn't know what the baking time would be (just that it would be much longer than it should).  Or, I could do something about it.  Needless to say, I chose the second option and followed through by purchasing an oven thermometer to really see what was going on.

There are many brands and types out there, but fortunately a quality oven thermometer doesn't translate to big bucks.  Expect to pay under $10 for one that'll do the job.

So what's the best way to calibrate your oven now that you've got a thermometer?

  1. The easiest way (but also least efficient way) is to just over or under heat your oven by a certain amount until your new oven thermometer (inside the oven) reads the temperature that you're going for.  Once met, figure out the difference in temperature between what your outside dial shows and what your inside thermometer shows.  Keep this final number mentally noted for the next time you go and bake something.
  2. If you want something a little more exact, start by heating your oven to a standard low temperature, like 275°F.  After your oven has finished preheating, jot down what temperature your oven actually is inside.  Open your oven door for a few minutes to let the oven cool down, and then repeat this process two more times with both a medium and high standard temperature (such as 350°F and 425°F).  Take an average of your three differences and use the average as a guide in the future for the amount to over or under compensate for.
  3. If you're feeling extra nerdy ambitious, you could go one step further and create a graph to see what type of relationship you have between your outside and inside readings (linear, exponential, etc.).  Using my graph below, I was able to create a condensed table for my oven (that's proudly posted) that states what to crank my oven to for 11 common values from 250°F to 500°F, using 25°F increments.
And now what about the results?  Was my $7 purchase worth it?  You can see above that some of my temperatures had a difference as much as 50°F!  As extreme as that may sound, it's a fairly common number with older ovens.

After baking my first dish using my handy-dandy chart, I am proud to announce that both the internal reading was spot on, and that my batch of bagels turned out perfectly after using the recommended baking time!  Whether your oven is brand new or decades old, there are going to be inconsistencies between the input and output temperatures.  So why not eliminate future guess work and purchase an oven thermometer?

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  1. TJ,

    How much do you trust the accuracy of the oven thermometer? And how would you test the accuracy? I have various gauges to measure air pressure in my bike tires and they all provide me with different readings! Perhaps you could put the thermometer in boiling water and see if it reads 212 degrees. But even if it is accurate at 212 degrees that doesn't necessarily mean it is accurate at 450 degrees.

    Bill K

    1. As far as ways to test a specific oven thermometer’s accuracy, I would shy away from the ice water (32 deg. F) and boiling water (212 deg. F) methods. Along with the fact that your oven thermometer may not be water proof, oven thermometers aren't made to perform in this low-temp range. Rather, this is a method best left for food-based thermometers, like a bimetallic stemmed thermometer.

      Although there are other methods out there for testing accuracy (like the sugar method), I believe that the best way would be to borrow an oven thermometer from a friend and compare the two over a range of temperatures, or else purchase a trusted (and tested) oven thermometer. The people at America’s Test Kitchen (who I back 100%), came out with their list of recommended oven thermometers about two years ago. After six months of trials, they came up with the following list of trusted brands:

      #1 - Cooper-Atkins Oven Thermometer ($6, basic, sturdy, and accurate)

      #2 - CDN Pro Accurate Data Hold Oven Thermometer ($12, very accurate, but somewhat awkward to attach to oven racks)

      #3 - Taylor Connoisseur Series Oven Thermometer ($18, accurate, but large and led to discoloration for high heats over time)

      #4 - CDN Multi-Mount Oven Thermometer ($8, fairly accurate, but led to fading over time)

      The bottom line is that as long as your thermometer is of a trusted source, you can have faith in its accuracy. Expensive models do not necessarily translate into better accuracy (as shown above).

    2. TJ,

      I too trust ATK. Especially after I read their 3-page treatise on how to make a hardboiled egg.

      I think your recommendation of averaging two trusted thermometers would produce a graph that could be trusted.

      I was also thinking, that after making/deciding on a conversion ratio (calibrating), that if things are consistently getting done per the recipe directions, then you pretty much know you have figured things out. And can then bake without fear.

      Regards, Bill K