Cast Iron Cooker vs. Granite Ware -Thermal Data-
Formerly a huge advocate of cast iron cookers, I have become evangelized by TrailRunner, aka Caroline. After much dissent, I conceded to Caroline's persistence and decided to give the Granite Ware (GW) a try. I thought, how could a light weight cover hold anywhere near the heat as a heavy weight cast iron cooker (CIC)? Against everything my common sense was screaming at me, I started testing.
Originally I tested by simply shooting the heated vessels with an Infrared Heat Gun. The temps were leading me to accept Caroline's assertions. The gun showed that the GW heated up and also recovered heat much faster than the CIC. The GW also lost heat much faster than the CIC. For months I rejected the use of the CIC in favor of GW. A couple of days ago I spoke with my nephew who is, believe it or not, a rocket scientist (engineer). I wanted to learn about emissivity. He works as lead thermal engineer for the US Space program at Martin Marietta. During our conversation we came up with the following idea. And after today's test the rest is history...
Last evening I started a couple of 550g boules. They were placed into the retarder and a temperature data log was setup. The data log for the dough retarder can be viewed HERE. NOTE - if you play with the log you will discover that a number of options are available e.g. the ability to position the cursor in the timeline and get all 3 temperature readings. This morning the test began. The goal was to compare in real time, the ambient temperatures inside the vessels used to bake the bread.The oven was set to bake @ 500F for the first 20 minutes and then once the covers were removed reduced to 425F convection for a total of 30 minutes cook time. A Fibrament-D stone was used as the deck. The GW vessel used can be seen HERE. The CIC can be seen HERE. The GW cover and also the CIC top and bottom were predheated @ 500F for about 1 1/2 hours before the bake commenced.
The tips of the temperature probes needed to be situated in such a way as to have them exposed to open air inside each vessel. To accomplish that, the probes where placed through the bottom of each dough and left protruding through the tops. The probe on the open deck seen above is for the ambient temperature.
The doughs were loaded and the data log starter. Below is a screen shot, but the actual data log for the bake can be seen HERE. Note the chart at 9:27, commence bake and 9:49, open oven and remove lids. Below is a static screen shot of the graph.
The following data may be of interest. All temps are Fahrenheit.
The initial temperature of the doughs were 44°.
These temperatures were taken just before the dough was loaded. Stone - 529, floor of oven - 568, CIC - 504, GW - 512.
Both vessels were measured with an infrared heat gun for temperature at the following times. 30 seconds out of oven: CIC - 426, GW - 336. 1 1/2 minute out: CIC - 352, GW - 175. 3 minutes out: CIC - 304, GW - 131. 5 minutes out: CIC - 259, GW - 117. After only 3 minutes out of the oven the GW was easily handled. A great safety feature.
Conclusion - Granite Ware is light weight and inexpensive. To be most effective a stone or something similar should be used for the deck. Although it loses heat extremely fast, it also recovers heat equally as fast. The bread in the Granite Ware vessel almost constantly hovered around 65° F above the Cast Iron Cooker.
I am always inspired by the scientific information shared by Doc.Dough. I only wished I could comprehend more of it :-( I did my best to execute this experiment with his expertise in mind. I know had he conducted it, we would have more scientific information available. But this is a country boy's best effort ;-)