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December 29th, 2018, 2:47 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, 2 each on the lower and the upper grates, approximately 6" away, on the left and right, of the pork butts. 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 the time to cook 2 pork butts. Unlike Part 3, this test will only follow the process of cooking, from startup of the cooker to when the pork butts are done. The test will follow the Yoder Smokers suggested startup procedure, (download/Best%20Practice%20and%20how%20to/Recommend%20procedure%20for%20starting%20up%20a%20Yoder%20pellet%20cooker.pdf) allowing the cooker to heat up at the default 350 degree temperature, then changing the set temperature to 250 degrees when the pork butts are placed in the cooker, and changing the set temperature to 325 degrees after wrapping the pork butts and placing them back in the cooker.

These pictures show how the 6 Fireboard probes were arranged in the cooker. The 4 Fireboard meat temperature probes were placed approximately 6" away, left and right, of the pork butts, and the 2 Fireboard ambient temperature probes were placed in a location common to owners communicating with us about temperature issues when cooking.



The next 2 pictures show the two 10 pound pork butts placed in the cooker in relation to the temperature probes. This allows us to see the effects on temperature readings in the cooker, compared to the probe placement results from Part 3.


Here is the Fireboard Session Graph.
fireboard session.jpg

Here is the graph that I made showing the data through the entire time the cooker was running.
temp test 2.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 and Part 3, this is the normal start up time, but, unlike Part 2 and Part 3, the set temperature of the startup was done at the default temperature of 350 degrees.

Section 2 - 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, left to right and front to back, and directly behind the ambient probe. 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..
Average temperature readings prior to wrapping the pork butts
Lower Left289.7
Lower Right262.3
Lower center above grate246.3
Upper Left233.6
Upper Right262.1
Upper center above grate231.8

Controller Display temp252

The cooker is functioning properly and maintaining the desired set temperature of 250 degrees, but unlike in Part 3 where the Fireboard temperature probes were placed close to the meat, the placement of all of the Fireboard probes 6" away from the pork butts allows the Fireboard temperature readings to be more accurate and better correlate to the controller display temperature.

Section 3 - 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.

Section 4 - 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. 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 Left325.5
Lower Right315.6
Lower center above grate275.9
Upper Left267.8
Upper Right285.6
Upper center above grate263.8

Controller Display temp335


Following the Yoder Smokers suggested startup procedure (download/Best%20Practice%20and%20how%20to/Recommend%20procedure%20for%20starting%20up%20a%20Yoder%20pellet%20cooker.pdf) provided a more stable cooking temperature, as the entire metal mass of the cooker was allowed to heat up to a temperature higher than the cooking temperature, which negated the parasitic heat loss associated with the cooker achieving normalization.

Placing external temperature probes closer than 6" to anything in the cooker will skew the resultant temperature readings. The difference in temperature probe placement illustrated between the testing in Part 3 and in Part 4, clearly illustrate the dramatic temperature readings differential of improper temperature probe placement in the cooker.


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