Statistical Analysis of Turkey Cooking




Introduction: Statistical Analysis of Turkey Cooking

About: Engineer making renewable energy products for African entrepreneurs.

The following is my analysis of cooking a turkey. I will be measuring temperature and time for a 20 pound turkey cooked in a Rival brand roaster.

Step 1: Instruments

TEMPRITE Digital Cooking Thermometer with Alarm
Resolution: .1 degrees
Temperature range of -40 to 450 degrees F
6 inch metal probe with silicone coated wire
"Slow" response time and low temperature range suggests this uses a thermistor

Rival Top Browning Roaster Oven
Capacity: 18qt
Possibly broken temperature knob. It feels as if no internal component is moving.

Step 2: Calibration

Whenever you take measurements, your instruments should be calibrated (if applicable). The probe of the TEMPRITE thermometer was submerged in ice water. Phase change (freezing/melting point) for water occurs at 32 degrees F. Therefore, the ice water should be approximately 32 degrees F.

5 Measurements were taken. Crushed ice was poured into a cup and then filled with water. Between each measurement, the water was poured off, the ice was topped off and the water refilled.

1: 32.4
2: 33.6
3: 31.5
4: 32.0
5: 32.2

Mean: 32.4 degrees F
Standard Deviation: 0.777
r squared: .13

For the purposes of the analysis, it is assumed that the instrument is accurate. Deviation from 32 degrees F can be attributed to minerals and other "imperfections" in the water in addition to human error etc. Horrible r squared value can be attributed to very low sample size (an ideal r square value is 1 or very very close to 1).

Normally, I would have also tested on boiling water. Unfortunately, my stove and oven at home is out of commission (and on thanksgiving too :( ). For some reason it won't hold oven temperature and will be replaced the Saturday after thanksgiving...

Below is a graph with the calibration data - if the r squared value was close to 1, the pink regression line would be very close to horizontal (zero slope).

Step 3: Background and Methodology

Cooking time is dependent on cooking temperature, food starting temperature, food volume, food shape (spherical), food surface area, and food density.

Lets assume spherical turkey and that all turkeys have the same (or very similar) density. The volume of a given turkey will be (4/3)*pi*r3 where r is dependent on food density. So for a given r, we can find the surface area as 4*pi*r2 (FYI: Volume of a sphere is the Integral of Surface Area).

The following was calculated assuming a 10lb turkey has a radius of 10 units.
So a 10lb (and a radius of 10) turkey has a volume of : 1333 * pi
and a surface area of: 400 * pi
and a radius: 10

Now let us double our mass and go for 20lb. Remember that the density is the same (and our only mathematical constant).

The following is based of the 10lb turkey calculations (keep in mind, these are quick estimate calculations).
Volume: 2666 * pi
Surface Area: 634 * pi
Radius: ~12.59

What we find is that if we double the mass, the volume is increased by a factor of 2. However, the surface area is only increased 1.59 times. So we have twice the amount of mass to heat, but only a 1.59 times the surface area to move said heat. On the bright side, our heat does not have to travel twice the distance :)

So it can clearly be seen that cooking time estimates is some sort of voodoo best described by thermodynamisits (? :P) OR by those with meat probes.

Before collecting data, the instruments were calibrated (if applicable) and then cleaned. The probe was placed in the thigh in what is usually considered the "normal" location to get an accurate temperature reading for dark meat (which takes longest to cook).

The data was then recorded at regular intervals. When the correct "doneness" was reached, a final reading was taken before removing and cleaning the probe. Using the collected data, a basic analysis was completed although time constraints due to final examination schedule made this a bit hasty.

Step 4: Measurements

Measurements began at 47.1 degrees F with an ambient temperature of 71.2 degrees. For about 15 minutes the turkey was rubbed and seasoned buttered and punctured. The pan was filled with potatoes veggies and neck.

We reached 160 and to my horror we passed 200 degrees F. Something was horribly wrong here. We opened up the roaster and discovered that the probe had worked its way out a little (exposed to the much warmer surrounding air). The probe was pushed back in, but the temperature stayed around 210.

Yes, something fowl was afoot!

The deadline is fast approaching, I have some Gauss-Legendre quadratures to attend and the analysis is not yet complete. So hastily, I put some things together so everyone can witness the overcooked (and dry) turkey data. That being said, it wasn't bad - it was quite good and fit well on the plate alongside the 2 pounds of fresh whipped potato.

Perhaps one day I will return and give you a proper cubic line estimate and an uncertainty analysis (that's if I'm really bored :P).

Step 5: Afterthought

I had meant to do this project with a thermocouple wire I made a couple weeks ago. I was going to build a bridge, make my own calibration curve and take measurements with a multimeter. I would then do some simple math on said calibration curve and get data.

As fate would have it, the wire insulation is not food safe. Bugger. But here's a picture of the spot welded thermocouple :)

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    9 years ago on Step 2

    Regarding your calibration in ice water, I don't know why you're calculating the r-squared of temperature measurements versus trial number. The standard deviation is the summary which shows how much your measurements "wander" from 32 F. Regardless, your freezing measurement wanders only a few degrees at most from the anticipated value, which I think is fine for this work.


    16 years ago on Step 4

    Have you repeated this effort, possibly with a different size bird (hence different dimensions.) I find it curious, you have an obvious scientific bent, but your measurements are in fahrenheit rather than Celsius, or even Kelvin. Oddly enough, cooks and bakers in Canada and presumably in the UK still use fahrenheit; even tho' magazines with recipes talk about 300C (450F) pretending their readers are up-to-date and the minority have to use the conversion. Friends of mine tell me that German carpenters still measure nails in inches, and housewives still by a pound of butter; and Napoleon convert Germany 200 years ago.


    Reply 16 years ago on Step 4

    Nope, there hasn't been an occasion for turkey (or whole bird for that matter) :/ It's a pity though :P

    I displayed the measurements in Fahrenheit because I figured most of the target audience (Instructables readers -- mostly from USA) would feel more comfortable with it. I however, have no problems with either scale (that is, you tell me it's 17 degrees outside and I'll know to wear a sweater) :P

    As for scientific purposes... the scale you choose is of no consequence -- conversions can be made quite easily and quickly.... Hell, if I wanted to use Rankine (absolute scale of Fahrenheit -- like Kelvin) it would still have the same heat content :P As long as you stay consistent, the mars lander will be fine :D

    As for your citations of usage of the imperial system -- it just goes to show that tradition is deeply rooted in every society. It doesn't make it wrong or anything either :D That's also very interesting; I had no idea.

    Last bit.... To be honest, I prefer Meters-Kilograms-Seconds over Feet-Slugs-Seconds ;) It's just so easy to convert between minor units and when I calculate my mass, I'm happier saying 58Kg over 4slug :P

    Tool Using Animal
    Tool Using Animal

    16 years ago

    Automate the data logging, you could set a webcam to capture the temp every x minutes, convert with ocr and paste into a spreadsheet. BTW Considering the average quality of your instructables, I was expecting the calibration to be done with a homebuilt triple point cell.


    Reply 16 years ago

    I never even thought of making (or using) a tpc. Considering I have only heard of and never physically seen one, that should be an interesting project. Although, I think you're supposed to use some sort of special water. I love how these projects breed my next project with these suggestions :P Next year, I'll look to capture and OCR :)


    16 years ago

    You probably put your probe too close to a bone. They get much warmer and can really throw off your measurements.