The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Dual Fuel Range

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dough-re-mi's picture
dough-re-mi

Dual Fuel Range

While I really want a brick or clay oven (and a large enough piece of property to hold it), it looks like I have an opportunity to replace my Amana gas oven. I used a thermocouple thermometer to measure its temp, and it swings so wildly I am surprised that the bread I've made has turned out as well as it has.

The oven reviews I've seen are all over the place. I would like to be able to add humidity by spraying inside the oven, and I would like a stove top that is easy to clean, with knobs that don't get hot. I hate that our oven has a fan that cycles on a lot, and I would prefer an oven that didn't have that 'feature'.

 

Any suggestions? I have read all the posts here I could find on this, and have not seen a clear conclusion. My sense right now is to get a Bosc.

 

John

Chuck's picture
Chuck

...it swings so wildly...

I'm curious just what "wildly" means  ...can you put a number on it?

The way ovens work is they cycle back and forth from a little below the desired temperature to a little above. The cycles are usually fairly fast - just a few minutes (depending mainly on how good the oven insulation is). I'm not at all surprised when the swing is up to 25F each way, i.e if I desire 400F, the actual oven temperature may cycle between 375F and 425F. Cycling 25F each way works just fine for baking things in the oven -including bread. If it's less than 25F each way, it's nothing to be concerned about.

(This means if you're trying to figure out just how hot your oven really is, look at your oven thermometer several times over several minutes, write down every number, then when you're done find the middle number and use that. Looking at an oven thermometer only once can be pretty misleading, as chances are it's caught the oven either near the top or near the bottom of the cycle. Don't "calibrate" an oven based on only a single thermometer reading, as doing so is likely to make it worse rather than better.)

Hence my curiosity: does your old oven swing significantly more than 25F each way?

dough-re-mi's picture
dough-re-mi

The magnitude of variation I saw made me want to get a logger for my thermocouple thermometer, which would log temps automatically as often as every minute. That's when I thought this was due perhaps to a faulty limit switch, the component that reads the temp and decides to either fire the burner or turn it it off. Now I think my oven might be operating within the acceptable limits of a cheap gas oven. 

The temp was 50-85 degrees on either side of the set temp, based on 5-10 measurements for a given set temp over 20-30 minutes with an accurate probe thermometer in place in the stove chamber. this was done at two different set temps (250 and 465, for a slow-ccok pork dish and for my bread). It is important not to allow the pork temp get too hot in order that the meat structures break down properly to produce tender meat that has cooked a long time.

I had to stand by the oven, either opening and closing the door or turning off the oven and turning it on, the way one would open and close a window and turn the heat on and off in a Toyota pick up truck in the winter.

Investigating further, it seems that electric stoves keep a tighter or more stable range of temps between the highest and lowest reading around the 'set' temp than do gas stoves.

 

Chuck's picture
Chuck

Yep, if "wildly" is 50F-85F on each side of the desired temperature, baking will be problematic; something is very wrong. And although gas ovens may indeed typically have a little more temperature variation than electrics (I've little first-hand experience with gas, so I'm not sure), I don't think even that could explain anywhere near 50F-85F. Has anybody else with a gas oven noticed anything remotely like this?

Possibilities that come to mind for why this is occurring:

  1. this is a really really really el-cheapo range
  2. the pressure of the gas is nowhere near what the oven expects (could happen if there's a "pressure reducer" valve where the gas enters the house, and that valve has rusted so it no longer works - the gas company should be able to both diagnose and fix this)
  3. the oven thermostat is kaput, needing a service person to replace (or maybe just radically adjust) it
  4. there's a "vent fan" in the oven and its control is kaput so it goes on at the wrong time
  5. the insulation in the oven walls and vent has deteriorated quite badly and needs to be entirely replaced
  6. the thermocouple is giving crazy readings because the other end of the thermocouple wires are touching a rack or an oven wall, and the conduction through the metal is messing up the readings
  7. the thermocouple is measuring the wrong thing- thermocouples in ovens should have their tip wrapped in something like a 1-inch square piece of tinfoil, otherwise they measure the temperature of such a tiny area, their readings don't really reflect the oven as a whole
dough-re-mi's picture
dough-re-mi

I appreciate your clear thinking and logic; thank you.

I decided to remeasure everything to get some good numbers. I pulled the baking stone out of the oven, set a rack in the upper third of the oven, and draped the thermocouple lead (http://www.thermoworks.com/products/probe/tc_penetration.html  model 113-178) over the rack so the tip was hanging down in the middle of the oven. The oven door closes well around the probe, and I read the temp from the thermometer on the counter. When I did the measurements before, the thermocouple tip was near the baking stone, and I now believe that distorted things.

I also dug out the owners manual, and looked more carefully at my oven. It turns out I have a gas cooktop and and an electric wall oven, installed to look like a single range (!). Hmm.

I set the oven at 465 and took measurements every 5 minutes for 45 minutes. I don't have the chart in front of me, but the mean of the temps after discarding the first two was 85.6 degrees too low (379.6). The max temp (taken at the second reading) was 455. The next highest temp was the last one, taken at 45 minutes; it was 402. (These numbers are from memory; my chart is at home).

The oven allows me to reset the thermostat by 35 degrees, so I did that. I am not sure if it will allow me to do that two more times. If not, I will have the thermostat changed, and I think (hope) that will solve this. I feel like I am saving a couple thousand dollars, so I am actually pretty happy.

I also learned an important detail ab0ut the fan that cycles on and stays on throughout the bake and blows hot air down the outside front of the oven. It is actually circulating air around the cabinet, and not removing the hot air from within the oven. It is an annoyance, but seems not to be affecting performance.

Chuck's picture
Chuck

Having a fan (that works at high temperatures) inside an oven to circulate the air/heat makes it a "convection oven". Convection ovens are becoming quite popular in the U.S. (And my understanding is they're already almost universal in Europe). So if you've already got one, you're ahead of the game.

Because they heat so effectively, the usual rule of thumb is to take whatever temperature the recipe says and reduce it by about 25F to figure out where to set the knob. Some ovens (perhaps including yours?) internally deduct this 25F from what the knob says  ...if so your temperature may not be so far off after all. The pros of an oven doing this are a) the knob says exactly what the recipe says and b) you don't have to do any calculations in your head.  On the other hand the con of an oven doing this is it can be pretty confusing if you don't know about it.

Chuck's picture
Chuck

I was just looking again at the numbers you remembered. Taking the rough approximation that the oven cycles between your low number of 380F and your high number of 455F, the median actual temperature is (380+445)/2 = 417.5. (And that's a very rough approximation that I'm not too sure about. What I would have done is discard all the readings up until it first started to go back down again  ...rather than just the "first two", which seems rather arbitrary.) Assuming your oven deducts the 25F internally, 465 on the knob should be (465-25) = 440 on the thermocouple. That gives an error of only (440-417.5) = 22.5 degrees Fahrenheit, well within the 35 degrees allowed for "calibration".

(BTW, it's very common for ovens to come from the factory a little under temperature and need "calibration" as part of installation. If the installer was in a hurry and didn't bother to "calibrate" the oven, it would likely behave the way yours is behaving.)