The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Using an IR Thermometer

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xaipete's picture
xaipete

Using an IR Thermometer

I just got my new infrared thermometer and I have a few questions.


What does D:S (12:1) mean? I understand there is a ratio of 12:1, but I don't understand what it means in practical terms.


Where should I measure my hearth loaves? Center side? Center top? And will that measurement be an accurate measure of the internal temperature?


--Pamela

sphealey's picture
sphealey

This web site has a lot of useful information.  Quoting:


===


What is the distance to spot ratio?

D/S Ratio- Distance to Spot ratio refers to a very important feature of your infrared thermometer.  This ratio is the size of the area being evaluated by the infrared thermometer as it relates to distance.  In other words, the area being measured becomes larger as the distance increases.  This has a profound impact on the accuracy or precision of the reading.  If the target you are measuring is 6 inches in size, and your infrared thermometer has a D/S ratio of 8:1, than the maximum distance you can reliably measure the temperature of the target is 48 inches.  Beyond this distance, not only is the target being measured, but whatever else falls within the "spot" is being measured as well.  This means that if a very hot object is the target, and it is in cooler surroundings, than measurements taken beyond the maximum distance will include cooler elements, and lowering the "average" of what is in the "spot".

D/S Ratio X Target Size,   or   8:1 X 6 = maximum measure distance of 48 inches. ===


One thing it does not discuss however is an emissivity setting, which in my power plant experience does come into play when measuring the temperature of refractory (baking stones).


sPh

xaipete's picture
xaipete

Thanks for the great D/S explanation and site link.


--Pamela

sphealey's picture
sphealey

Sorry about the messed-up formatting on that reply.  Once it was saved I couldn't fix it.  Wish the preview window really matched the saved version ;-(


sPh

ehanner's picture
ehanner

Pamela,


The IR thermometer is not used to measure the internal temp of the bread. I suppose you could cut open the loaf and take a measurement but that defeats the purpose. Measure the milk, the water, dough, flour and your forehead.


Eric

xaipete's picture
xaipete

Thanks, Eric. I figured as much. Next time I bake, however, I will test the loaf with my thermapen and the IR. Maybe I'll be able to figure out a relationship.


You are definitely right about the stone losing heat. I made some pita bread today and checked the stone before and during cooking. The portion where the pita was sitting lost nearly 100º. Amazing.


--Pamela

Pablo's picture
Pablo

Glad you're asking questions, Pamela.  I'm picking mine up on Friday.


:-P

ehanner's picture
ehanner

It's even a larger heat loss when you put a 2 pound boule on the surface of that stone. The heat never recovers. When I saw that it made me think about using a pan that would heat and recover quickly rather than a stone. Another thing is if you need to do more than one session, it's a while before a stone comes back up to temp after removing the first batch. Mean while the dough is proofing while you wait.


I know you will learn to value your new tool.


Eric

xaipete's picture
xaipete

Thanks, Eric. You've made me a believer! I love the IR gun. Now I'm just trying to figure out what to do with the stone.


--Pamela

ClimbHi's picture
ClimbHi

I find my IR gun valuable -- almost essential -- for taking surface temps of my WF masonry oven prior to baking. (This is more important for a masonry oven since it relies more on radiant heat from the oven walls & roof than a conventional oven does.) I also use it for stovetop frying to take the surface temp of the pan before adding the oil or other ingredients. I also use it to check that the waffle iron is ready for batter. That's pretty much it.


You may want to use it to take the temp of your baking stone so you can get consistent results when using it, but other than that, I don't think you'll find it much help in the world of bread in a conventional oven.


As you doubtless know, the surface temp of a loaf is not necessarily directly related to the internal temp. For example, the surface temp of a loaf in a very hot oven will rise much more quickly than it would in a cooler oven, but the internal temp will rise much more slowly. Similarly, the surface of cold dough placed in the oven will rise quickly, but the internal temp won't rise nearly as fast. Likewise, the internal temp of a large loaf will rise more slowly than that of a small loaf, whereas the surface temps of both will rise much more equally. This means that if you shoot for a set surface temp of the loaf, the internal temp may be fine, but it's just as likely to be too high or too low, depending on the conditions of the other variables.


I use mine to make sure I have proper conditions in the oven prior to loading the loaves. After that, for me anyway, the color of the crust has always been the best indicator for timing the bake.


ClimbHi
Pittsburgh, PA

xaipete's picture
xaipete

Thanks ClimbHi for telling us how you use your IRT. I'm anxious to check out all of those applications with my new thermometer.


Do you think there is any correlation between say the center side temperature of a hearth loaf and it's internal temperature? Mostly this is just a curiosity for me at this point.


--Pamela

flournwater's picture
flournwater

No, Pamela, you won't find a universal correlation between the surface temperature of your loaves and the internal temperature.  That's because there are far too many variables involved from loaf to loaf.  The density of the dough, the size (mass) of the loaf, etc. can never be consistent enough (outside of commercial production  -  and I wouldn't count on it under those conditions either) to provide a reliable correlation.  Physics is real fussy in that way.

ClimbHi's picture
ClimbHi

"Do you think there is any correlation between say the center side temperature of a hearth loaf and it's internal temperature?"


Well, if you use the same oven, at the same temperature, and bake the same size (weight and shape), same hydration, same composition loaf each time, then sure. Otherwise, it's anybody's guess what the relationship would be.


Don't get me wrong -- I'm not sayin' these things are useless. Far from it. It's just that they are very specialized. I use mine all the time for doing what it's good at. But I have an air temp thermometer through my oven door to register air temp, and a rapid-read thermometer for internal temps. Depending on the task at hand, all three of these might be used to good effect.


BTW, I used my IRT gun last evening to take My Lovely Assistant's temperature since she thought she had a fever. Nope - 99°. ;-)


ClimbHi
Pittsburgh, PA

SylviaH's picture
SylviaH

How do you take someone's temperature with the IRT, point it in their ear?  I can't wait to use mine in my wfo!


Sylvia

xaipete's picture
xaipete

I'm not sure on that, but don't point it any anyone's eyes (including dogs).


I'm enjoying my IRT. I've used it a number of times now to check the temperature of my starter, and my dough to see how close I am to the DDT.


--Pamela

SylviaH's picture
SylviaH

I've been pointing it at everything except eyes....even came with a little holster!


Sylvia

xaipete's picture
xaipete

I've got the same one as you complete with holster. It really is coming in handy. I've got some stuff out in the garage right now because it is 70º out there.


I'm really enjoying it. After Paul gets his (Friday) we could start a new thread to list all the bread-wise things it is useful for.


--Pamela

ClimbHi's picture
ClimbHi

I was just fooling around, but I pointed it at the spot under her tongue where a normal thermometer would be placed.


ClimbHi
Pittsburgh, PA