Checking One's Oven For Proper Temperature Calibration
Several times over the past week I have read mentions on various threads regarding checking one's oven to see if it is actually baking at the temperature that is set on the dial, or the digital pad, of the oven's thermostat..Thermometers that hang semi-permanantly in the oven are OK for this purpose, although I have never found them particularly easy to read..And, as has been mentioned, thermometers kept constantly exposed to heat wear out, thus becoming less accurate as they age..
A far better option, albeit a much more expensive one than hanging oven thermometers, is to use a oven test thermometer designed to check more accurately the operating temperature of an oven..There are two basic versions of these oven test thermometers..There is the old-fashioned analogue mercury-filled glass tube thermometer, and the more modern digital versions that have a wire-mesh covered flexible probe that extends into the oven attached to a digital readout that resides outside of the oven..
When I attended culinary school I was given as a gift that first year an analogue version of the test thermometer..It is the Taylor Instruments 5903 Professional Fold-Up Oven Test Thermometer, and I can highly recommend it for its accuracy..It told me that my home oven bakes about 20F-25F hot; and that over the years that virtually every commercial oven that I have used is innaccurate..Commercial convection ovens I have especially found to be inaccurate, as well as having many hot and cold spots..Some of my comments over the past several weeks on various threads regarding convection ovens reflect my knowledge of them by virtue of having tested several dozen of them over the years..
Anyone that is interested in accurate, repeatable results in their baking I urge to have their oven tested..Just as the speedometers and odometers on motor vehicles are seldom as accurate as most people assume that they are; so too do ovens rarely bake accurately at the temperatures that people set them at..
Bruce
You have some excellent points Bruce. When I worked in qualilty assurance for an electronics controls developer/manufacturer I learned that very few controls maintain their linearity and a thermostatically controlled circuit can vary widely over its full range. If I tested an oven for 200 degrees and found it was actually 205, the same oven might very well actually register 230 degrees when the control read 250 degrees. My endorsement of your comments is meant to remind those who are trying to remain entirely true to precision in their baking process that testing their oven temperature at 425 degrees for a bread that bakes at that temperature will give them an indication of what adjustment is need to maintain that temperature; but only that temperature. If they have a recipe that bakes at 450 degrees it would be a good idea to check the stability of the oven at that point too.
flournwater
The points regarding linearity in the above post are right on point..I meant to mention the following in my OP, but forgot to..The point I wanted to make that you brought up is to test your oven for accuracy throughout its ENTIRE range, not just the few temperatures that most baker's use all of the time..Here in the United States most baking is done between 325F through 450F, in increments of 25F, with over 50% of all recipes calling for a temperature of 350F..However, as you pointed out, an oven can sometimes be very close to the set temperature at one setting, and vary greatly from the set temperature at another setting that is quite close to the fisrt setting..Check all the temperatures on your oven!!!!!..
Most people probably do not realize this, but the vast majority of professional bakers do not bother with thermometers very much..A lot of the older ovens made before the 1960's-1970's had a LOT of thermal mass, as do most of the modern ovens that artisan baker's are purchasing for their use..These ovens take a fair amount of time in order to lower the temperature..They are designed, for the most part, to operate and hold the set temperature, with the door(s) constantly open; so opening the door(s) is not going to speed up the process of lowering the temperature very much..
Most bakeries tend to just set these ovens at one "All-Purpose" temperature that they use for the vast majority of their daily baking..Their recipes are generally modified, hydration wise, to reflect a single baking temperature for most of their breads..
If a bakery has a need for multiple daily temperatures to bake at, especially if they are baking pastries and cakes, they usually have a second oven seperate from breads where the temperature can be more easily changed..Or else they arrange the work flow so that the foods requiring the lowest temperatures are mixed and baked first during the day, progressing through the foods requiring hotter temperatures as the day's baking unfolds..
Commercial ovens with a lot of thermal mass tend to hold a set temperature fairly accurately..Most good bakeries have the thermocouple / thermostat checked for accuracy every year or so; and adjusted if the technician finds that it is inaccurate..The one exception that I have found to commercial oven accuracy are convection ovens..Of all of the ovens that I have tested over the years, convection ovens have had the greatest variance between the temperature set by the dial / keypad, and the actual temperature as measured with my oven test thermometer..Convection ovens also have had a greater number of hot / cold spots within them than any other type of oven that I have worked with..
Bruce
Unless you suspect a problem with the thermostat or can't find a way to bake at any where near the needed temperatures, I think there is no need to make a big deal out of what the exact temperature is. This a case of "measure with a micrometer, mark with a grease pencil and whack the bugger off with a chain saw".
We learn the personality of the oven from use. If the oven doesn't bake evenly we have to adjust our procedure. That's what learning to be a good baker is all about. Sorry guys this is where I part company with the engineers in the kitchen. I try to shape my procedures by understanding how the old timers did it in big wood fired ovens. Implementing careful testing procedures to discover what I can see anyway isn't productive. Bake a few loaves and adjust. Let's see I have some asbestos around here somewhere!
Eric
Hear hear, Eric! Thank you for saying what I would like to have said if I'd managed to find the right words.
-Elizabeth
I bought a high-end Thermador range for my new kitchen about ten years ago after baking for many, many years on a Vulcan commercial range. The Vulcan had the Snorkle technology, an early and crude version of convection, but it baked like a champ. I could load it up with 20 loaves of bread and they all come out exactly the same with no shifting around during the bake. I bought the new oven believing that it would be quieter, cooler (and with the new technology) bake just as well. I was wrong. After years of fighting with the company about the poor performance of the oven and having frequent repairs, the repairman told me that many of the new "professional" home ranges take at least an hour to reach a stable temp. They cycle with a wide swing of temperatures while they're heating up. He also said that the companies don't say this in their brochures--although the information would be very helpful to home cooks.
I now preheat for at least an hour, and I imagine that the instructions in many bread books say to preheat for an hour for the same reason--the heat just isn't stable before that...
Thanks for this valuable information! NOW I understand what I thought was a rather prodigal instruction in various books to preheat for at least half an hour.
Our oven is an ancient electric one from around 1970 and 15 minutes of preheating seems to be plenty for it.
-Elizabeth