How to measure temperature of heated vegetables correctly with an IR thermometer

[nightfire]

Situation: I am an aspiring hobby/home chef, and my newest toy for doing also temp measurements in electronics i repair is a Fluke 62 Max+ IR thermometer.
Nice thing, and most important, has adjustable emissivity from 0.1 to 1.0

So theoretically I should be able to measure the surface temps of all my pots and pans (low emissivity, around 0.1), and be able to look for the surface temps when I put vegetables like onions and celery wit carrots in a pot to prepare as a sofrito (spelling right? non-native speaker here).

The magic temp is around 140 deg. C, the so called "Maillard temperature", when roasting processes begin to take place.


Any words of wisdom how to do good readings with an IR thermometer, and on the emissitivity values used?

[PlainName]

High emissivity is better for accuracy, and I wouldn't want to be relying on something with a 0.1 value. Pots and pans are naturally reflective so you would need to be careful you're measuring the pots rather than something you can see reflected by them. A cast iron griddle seasoned black could be good.

You will hit a problem seeing the surface temperature once your food is in the pan. Even if you start off with the pan at exactly the desired temperature, when you add the food the temperature will drop. I think you might be better off with a k-type probe or similar rather than IR, although that would get in your way more. Depends on how nerdy you want to be about temperature.

[nightfire]

Yes, it is only one thing to measure the surface temp of a pan or pot- a trick is to coat it with oil to get better readings, from what I have read...
I also want to know the surface temp of the veggies that are on top of the heap, which easily can be 1 inch/2.5cm thick.

Question here would be: Can I trust readings with an emissivity of 0.95, or to which value I would have to reduce?

And also yes, a K-Type probably is more accurate, but I am not nerdy (or needy yet) enough to use this.

[PlainName]

Can I trust readings with an emissivity of 0.95

Depends on how accurate you need to be. When it comes to veggies you could measure their temperature (before starting) with a contact thermometer and see how closely the IR agrees at 0.95 - it will probably be close enough, but if not you can adjust the emissivity to account. However, once in the pot and being cooked that could change (with fluids and stuff going everywhere). Nevertheless, it would probably still be OK for your purposes.

IMO, I hasten to add - I am not an expert at either cooking or thermometry!

[Marco]

And also yes, a K-Type probably is more accurate, but I am not nerdy (or needy yet) enough to use this.

Owning some probe and oven thermometers isn't very nerdy, pretty sure they are all k-type inside.

[beanflying]

Where IR measuring falls over is on polished anything and it is also ordinary as a measure of 'cooked' or internal temperatures while cooking.

The height of idiocy was a 'Health inspector' (used to be the local building inspector) instructing me at a public event to use an IR thermometer on a Stainless cooktop to determine if the egg I was frying were cooked 'through' to 60C Roasted meats are always probed as an example and depending on the chunk size of your vegetables you will get a much better result with a probe over IR. Similarly thawing, heating and or cooking of Pies as an example an IR thermometer might read a long way out with the middle still being cold if not frozen while the outside shows as 'cooked or heated'.

BUT

Where an IR gun even the cheapies are great is for a quick sanitary idiot check on progress or on slower cooked/heated products or where you are heating and holding food for service and want to keep it above or below a temperature range for safety. So Soups, Curries etc on the hot end or Desserts and Dairy on the low end (providing the emissivity issues can be overcome).

Different occasion same Health Inspector was having 'issues' with his high end IR thermometer not reading the Temperature of the Milk in my fridge or the shiny sided fridge temperature. The fridges had RTD's fitted and external displays but he knew better

[nightfire]

Yes, the dreaded health inspection show...

Years ago, I worked in retail- supermarket, to be precise. In germany you had back then HACCP regulations, so when new stock arrived, like milk or butter etc. you had to conduct some tests if the surface temp was within limits and in some cases the core temp had to be taken. SO in the store I worked we had an IR thermometer and a probe to stick in the goods.

Yes, I know that a fixed probe is way more accurate than an IR thermometer, but I had hopes I would not have to use them much, because IR is
a) simpler to do
b) I do not have to put in some thermoelements in the food and wait
c) the thermometer itself has to be cleaned after use to not contaminate the food with next measurement