why does oil temperature rise when I put food in the pan

Question

I tried deep frying in oil using a thermometer for the first time today, my usual method is to test temp with a small amount of food.

I was using a wok filled 1/2 full with vegetable oil. I heated it until the thermometer read 350 deg F. I then put in some Somosa that were frozen. A lot of steam and bubbles were created. I lowered the gas flame and noticed that the temperature had risen to 390 degF. My instinct tells me that the oil temp was likely to be really at 390 because the Samosa cooked faster than I expected.

I tried this a few times and consistently got the same results even with non-frozen food. The temperature did not change if I stirred the oil.

Could there be something wrong with the themometer?. I calibrated it with boiling water before I started.

Have I discovered a new form of energy? :)

Answer 1

It depends on the type of the thermometer and the position of the sensor inside of it. In all likely hood, you're not measuring the oil temperature but the air/steam above the surface.

When you put the food in, it produces more flow due to the water evaporating from the food and leaving the oil and registering on the sensor.

This is sometimes tricky, because some sensors are right at the tip and if you let it sink to the bottom you have yet another problem of reading the burner contact point and not the fluid.

Your best bet is to try and keep your sensor probe somewhat horizontal and almost fully submerged..

Answer 2

@mandomando has it right, I was measuring the air temperature and not the oil. I have done some more experiments and observed interesting results.

I tested two analog probes - a small Taylor and a candy/fryer CDN from Sur le Table. Both showed the same results - unless the probe is at least 2 inches into the food it can read as much as 50 degF too low. Looking at the CDN web site http://www.cdnw.com/sites/default/files/English_IRXL400en_0.pdf, I found a note saying that the probe will be inaccurate unless the probe is inserted up to a small dimple in the side of the probe. On both of my probes the dimple is 2 inches from the tip.

Conclusion - be very careful when using analog probes. In my case, using a fat frying thermometer submerged just 1/2 inch below the dimple resulted in a reading 50 degF lower than indicated.

I did the same experiment on a small Taylor digital probe and found that it read correctly at all depths.

Also, I found all of the probes indicated different temperatures. I would advise anyone using them to test them in a pan of boiling water before use.

Answer 3

I just had the same problem.. and then compared with a digital and found it was reading false temperatures more than 70degrees lower. I realized the analog thermometer has to be submerged over half its length. Mine was only touching by the tip because that’s what I was used to with my meat thermometer. I do like the analog one because takes no batteries and reads quite high, just need to get the knack of it first. Was very strange to put the chicken in my oil and it starts climbing higher and higher in temp. I am always paranoid and cautios when deep frying so when the canola oil was smoking splattering and popping louder and louder at 235 degrees, I was very confused and Freaked out..so mora of story.. experiment with new thermometers and see how they work.. Trust me, after a few batches of almond brittle tossed out and 500 degree fried chicken..I learnt the hard way..