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December 24th, 2018, 1:16 pm
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This article will use some hands on testing to illustrate the lessons learned in the previous article, and in addition, go through cooking 2 pork butts to show what happens to the temperature in the cooking chamber.

We will use a temperature logging tool that is readily available to anyone, to run some simple tests and show how the gradient heat works in the Yoder Smokers pellet cookers, and how an aluminum pan, introduced into the cooking chamber, affects temperature performance.

We will use a Fireboard temperature logger to gather the data and chart the test results: https://www.atbbq.com/fireboard-fbx11-w ... ition.html

The photos and test results from this test are from a well used Yoder Smokers YS640 that was built in early 2012. This cooker has cooked thousands of pounds of meat, burned through tons of pellets, and has been the guinea pig for engineering and programming changes. It is currently running U29 firmware and configured like the cookers currently leaving the factory, with the exception of the original prototype of the 2 piece diffuser. The pellet fuel that is exclusively used is a 50/50 mix of BBQR's Delight pecan and cherry. In consideration of this, if the reader attempts to exactly duplicate the listed results, there will be differences and variations in the data, but the overall findings should be the same.

We will use 6 Fireboard temperature probes for this test. There will be 4 Fireboard meat temperature probes, one each on the lower and upper grates at 11" from the hopper wall, and one each on the lower and upper grates at 22" from the hopper wall. There will also be 2 fireboard ambient temperature probes mounted toward the mid point of each grate, one on the lower grate and one on the upper grate, mounted in Fireboard probe holders 1" above the grate surfaces. The goal is to simultaneously record 6 temperature locations over a 2 hour test period by following our Yoder Smokers factory temperature test (download/Best%20Practice%20and%20how%20to/Yoder%20Pellet%20Temperature%20Test%20v2.pdf), and then cooking 2 pork butts, one on the lower grate and one on the upper grate, illustrating the gradient temperature in the cooking chamber, from side to side and bottom to top, and the resultant effect on the Fireboard temperature readings without moving any of the temperature probes inside the cooking chamber after placing meat on the grates.

These pictures show how the 6 Fireboard probes were arranged in the cooker. The 4 Fireboard meat temperature probes were placed per the instructions from the Yoder Smokers factory temperature test, and the 2 Fireboard ambient temperature probes were placed in a location common to owners communicating with us about temperature issues when cooking.

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This is how the Fireboard probe leads are plugged in to the Fireboard unit; #1 is lower grate level at 11", #2 is lower grate level at 22", #3 is lower grate in probe holder, #4 is upper grate level at 11", #5 is upper grate level at 22", #6 is upper grate in probe holder
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The next 2 pictures show the two 10 pound pork butts placed in the cooker in relation to the temperature probes. None of the temperature probes were moved, which allows us to see the effects on temperature readings in the cooker compared to the 2 hour temperature test.
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The following pictures were of the pork butts after placing in half pans and covered in foil. The temperature probes still remain in the same locations.
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Here is the Fireboard session graph for the entire time the cooker was on, including the 2 hour temperature test and the cooking of the pork butts.
fireboard session.jpg

Here is the graph that I made showing the data through the entire time the cooker was running.
temperature test and pork butts.jpg

Let's take a look at what happened. To make the graph easier to read, I didn't place any analysis in the graph, but rather sectioned the graph and numbered the sections from left to right. The analysis for each section follows.

All of the data came from the captured data from the Fireboard session, with the exception of the controller display temperature, which was captured directly to a laptop using our internal proprietary testing tools. The fireboard session data was downloaded at the highest resolution of data points, and then put into a spreadsheet to chart and calculate the results shown in the chart.

The first thing to understand is that the #1 probe is consistently reading hotter than the set temperature. This is the result of using the original prototype of the 2 piece diffuser in the test cooker. Using the standard diffuser, or the production model of the 2 piece diffuser, will provide differing results than what was captured during this test.

Section 1 - As stated in Part 2, this is the normal 30 minute warm up time.

Section 2 - This is the next 1.5 hours of the cooker running the Yoder Smokers factory temperature test. The cooker lid has not been opened since it was closed during startup.
Average temperature readings over the 1.5 hour temperature test
Lower 11"259.1
Lower 22"282.2
Lower center above grate252.2
Upper 11"239.3
Upper 22"254.2
Upper center above grate245.6

Controller Display temp249

Section 3 - Opened the lid on the cooker and quickly placed two 10 pound pork butts, one on the lower grate and one on the upper grate, directly centered between the 11" and the 22" probes and directly behind the ambient probe, in the center of the cooker. The pork butt on the lower grate was placed with the fat cap down toward the heat diffuser, with the bone pointing toward the hopper end of the cooker. The pork butt on the upper grate was placed with the fat cap up and the bone pointing toward the chimney end of the cooker. In each case, the meat was placed per the results of the temperature test in part 2, i.e., the fat cap and bone toward the highest temperature potentials. I did not outline a 30 minute recovery period after placing he pork butts in the cooker, because the process was a done quickly and the metal mass of the cooker helped to immediately recover temperatures in the cooker.
Average temperature readings prior to wrapping the pork butts
Lower 11"235.8
Lower 22"219.4
Lower center above grate212
Upper 11"208
Upper 22"203.2
Upper center above grate212.4

Controller Display temp254.1

If you compare the temperatures from Section 2 and Section 3 of the graph, you can see that the cooker is functioning properly and maintaining the desired set temperature of 250 degrees, but the placement of all of the Fireboard probes in proximity of the pork butts is skewing the Fireboard temperature readings. This deviation is caused by the cooler temperature of the meat and the "bubble" of evaporation surrounding the meat during the cooking process. This is all normal, and expected. We field a lot of questions about why the ambient probe in a cooker is up to 50 degrees cooler than what is being displayed on the controller; this is the explanation.

Section 4 - Opened the lid on the cooker to check the status of the pork butts to see if they were ready to wrap. They both had the color I was looking for and the bark was hard set, i.e., couldn't remove the seasoning off the surface by gently using a fingernail to scratch across the surface. Removed the pork butts, placed them in a pan with some liquid and more seasoning and used foil to seal the pan around the pork butts, and then placed them back into the cooker. The probes were not moved from their locations. I raised the set temperature on the cooker to 325 and closed the lid. Because of the wrapping and the temperature change, this is charted as a 30 minute transition and not part of any average temperature calculation.

Section 5 - This is charting the remaining time of cooking the wrapped pork butts. The arrows on the chart show when I opened the lid to check the pork butts for doneness by probing for tenderness, The middle arrow is when I took the lower pork butt off the cooker as it was probing tender. You can see this by the chart as the temperature of probe #1 and #2 went up, but were still being influenced by the pan on the second shelf. An interesting thing to note is the temperature trending slowly upwards as the meat gets closer and closer to coming off the cooker. Also of interest is the cook time differential between the lower and upper pork butts, which is expected, as the lower pork butt is interrupting the airflow to the upper pork butt, which is also more pronounced after wrapping the meat in pans and foil.
Average temperature readings after wrapping the pork butts
Lower 11"273.6
Lower 22"267.4
Lower center above grate253.4
Upper 11"248.2
Upper 22"238.9
Upper center above grate238

Controller Display temp323.4

Yoder_Herb

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