11 Jun 2009

Cooking pit revisited - temperature logging

Spring and summer time equals cooking pit time. This time we did some more serious temperature measurements, showing interesting results. A brief report follows...

Every May/June we take our food culture students out for some primitive cooking, ref. the previous post Primitive food, heat transfer and a day out. This time we did some more serious temperature logging with the help of Type K 4-Port Temperature Sensor connected to a Pasco datalogger.* This enabled us to monitor temperatures automatically at four different places in the cooking pit at one time:
  • inside of the pit, at the bottom
  • inside of the pit, at the top
  • inside the trout cooking
  • 10-15 cm outside the pit, ca. 25 cm deep (to monitor the heat loss through the soil)
Temperature plot. Click for large version

Most noteworthy is the temperature difference between the bottom and top, since the food and rocks are laid in layers. This is very interesting in terms of where to place food the next time we'll use this method. One might also exploit this to cook different foods in the same pit (i.e. meat and chicken or fish); place the meat at the bottom and place the fish directly on top of the meat. Also, note that the fish, being wrapped in foil, levels off at 110 °C. I guess this is due to the large water content in a closed package. Hence, this isn't the method if you aim at sous-vide type results. The flavour and texture is however still very good, not at all mushy.

This time we dug two pits
  • Pit 1: lamb's leg and potatoes, somewhat less than 3 hr cooking time
  • Pit 2: Trout and chicken, 1 hr 10 min. cooking time (see temp. plot)

Data logger with 4-port K-type sensor. More pictures in previous post

We're on our way to publish a web based teaching plan on this topic, including historical, physical science, and food related information at www.naturfag.no/mat (Norwegian national school science web pages) and www.natursekken.no. All in Norwegian (but google and babelfish make increasingly good translations). I'll post a note when it's out.

Wandsnider, L. "The Roasted and the Boiled: Food Composition and Heat Treatment with Special Emphasis on Pit-Hearth Cooking." J. Anthr. Arch. 1997, 16, 1-48. (This ref. is most relevant for indigenous American traditional pit-hearth cooking, using rather different foods. For Scandinavian prehistoric methods, see the previous post and coming teaching plan)

www.naturfag.no/mat, English translation
www.natursekken.no, English translation

* The K type thermocouples measure a range of -200 - 1000 °C! Although the probe sleeves are limited to 482 °C, this is sufficient for use inside the pit

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