Temperatures & Thermometer Calibration / Meater+ / TelTru

[Braai-Q]

Hey Everyone

I've been seeing some difference in ambient temperature readings and I just wanted to get a 'forum view' on my experience. I've had a look for information online and in the forum but couldn't find anything that answered my question. I did do some wider research and the most illuminating (and entirely irrelevant search result) was an interesting scientific paper on thermoregulation in Komodo Dragons although I did come across an interesting article on heat cycling and oven accuracy from Thermoworks that I remember using some while ago. 

So I did a cook yesterday - simple setup, 1.6KG topside in a foil tray in the 19KK. Centre of the grill and I used the middle grill so it was dead centre of the KK. Foil tray was a little bigger than the meat but not much and I positioned it centrally to get even convectional airflow. Popped the meat in at 200°C and gave it 30-45 mins to heat soak. I put a Meater+ into the joint and the probe tip was at the very centre - it was inserted horizontally i.e. parallel to the grill. I was aiming for rare with a target internal temperature of 50-52°C and the internal temperature at the start of the cook was 9 degrees.

After I added the meat and the temperatures stabilised, the TelTru dome temperature stayed at 200°C for the entire duration of the cook. When I looked at the graphed temperatures, the ambient range on the Meater+ correlated in being constant but was much lower at 145-147°C for the same period. 

I know the refractory surface has a high thermal mass and should have uniform convective heat (reflected in the stability of the temperatures read from both gauges) but I would not have expected such variation on ambient when you consider that the measurement points are not that far apart. I could accept that they wouldn't be on parity because the probe is conductive and inserted into a much colder object but 55-57 degrees different?

I had a look at Meater's website and they talk about their ambient sensor (FAQ quoted below) being extremely sensitive to microclimates but I don't see the air circulation patterns being that significant on a heat soaked and unopened KK. But I'm not an expert on thermal dynamics. I also can't see the meat exerting that degree of influence on the ambient sensor but I may be entirely underestimating the sensitivity. 

I've done an ice point check on the probes and they're all calibrated fine. I could do an ambient check in our range cooker as a control but I'm not sure the answer lies there. 

Can anyone offer a qualified explanation?

Thanks

Quote

MEATER measures the ambient temperature directly at the black ceramic tip. Since most cooking appliances tend to have hot and cold spots, we designed our ambient sensor to be extremely sensitive to microclimates within the appliance, so that our probe can detect the temperature that your food is actually being exposed to. Because of these hot/cold spots, the reading can vary greatly depending on the location of the probe.

This is important to take into account when trying to compare the reading with another thermometer or a second MEATER probe, even a few inches away. Additionally, proximity to the colder meat itself can affect the ambient reading.

If you’re measuring against a built-in thermometer in your cooker, these tend to read either the average overall temperature or just the temperature right near the lid, and this will often be different from the temperature immediately surrounding the meat.

 

 

 

[tony b]

Interesting, and coincidental. I used my MEATER+ on a rotisserie cook yesterday and got some very squirrely ambient temperature reading - very sawtooth - and not from opening the lid. I've seen a similar behavior before. I suspect it's caused by juices running down the probe and coating the end of the MEATER, where the ambient temperature probe is. Given that the meat juices are a couple hundred degrees (F) lower than dome temps, you can imagine the swings that I was seeing. It played hell with the "estimated cooking time" algorithm - LOL! 

But, back to your point more directly. It's not just the MEATER probe, there's always a delta in temperature readings between the dome and the grate. Typically in the 25F - 50F range. I see it with my Maverick and Guru probes, too. Proximity to the meat has a small influence. One thing that I learned a long time ago and practice consistently, is to not clamp the probe directly to the grate - you get a false reading of the air temperature. I use a wine cork with a small nail in the end that I attach the alligator clip on the probe too. I cut notches out on the opposite end of the cork for it to fit in between the grate rods. 

[Braai-Q]

Thanks Tony. If that picture is of your rotisserie chicken, they must grow them differently where you are! 😁

I expect a delta. Absolutely. But I didn't expect that much of a difference. Maybe 10-15 degrees. I don't know why I haven't dug into it before. 

Good shout on the cork to isolate the heat effect of the grate. I ordered myself a Fireboard 2 on Saturday. I haven't had any new toys in a while so I thought it was high time. 

I emailed Meater to ask directly - I expect they'll give me a link to the FAQ and a pat on the head. Who knows.

[tony b]

On 10/5/2020 at 10:02 AM, Braai-Q said:

Thanks Tony. If that picture is of your rotisserie chicken, they must grow them differently where you are! 😁

Too funny! 

As you can see in this pic of the chicken, the exposed end of the probe was pretty gunked up.

Here's the MEATER graph. Initially low, as I put the probe in early inside the kitchen and it sat for a bit before I put it on the KK - that's the 1st spike. It sort of cruised up and then something happened and I saw the rapid increase to the 2nd spike. The drop right after was me opening the grill to check on what was going on, since it was behaving so squirrely. Temps rebounded after I closed it back up. That's when it really went wonky for the rest of the cook. Again, seeing how gunked up the tip of the probe was lead me to believe that's what caused the end of the cook to behave so crazy. Meanwhile, the dome thermometer was ready steady right where I set the vents! 

Edited October 6, 2020 by tony b