Posts Tagged ‘stainless steel’

Accelerated aging of wine

Monday, February 2nd, 2009

vinkorker
Can the natural process of aging wine in corked bottles be accelerated?

I recently found an interesting article on how an electric field can be used for maturation of wine (New Scientist news coverage of the article). Applying a AC field of 600 V/cm for 3 minutes resulted in an accelerated aging of wine and according to the authors of the paper, it made “harsh and pungent raw wine become harmonious and dainty”. They observed changes in concentrations of higher alcohols, aldehydes, esters and free amino acids. But I was quite surprised that they don’t say anthing about astringency and polyphenols (tannins). I’d expect some changes there as well, but alas it’s so much more difficult to measure the polyphenols than the low molecular compounds. A sensory panel identified both positive and negative effects of the electric treatment which helped identify an optimum treatment. Apparently several Chinese wine manufacturers are testing the technology on a pilot scale now. Many people have a romantic impression of how wine is made, but the extensive catalogues of “corrective chemicals” available to the modern wine maker should perhaps make you reconsider the romatic idea of wine making. Even professor Hervé Alexandre at the University of Burgundy has given the technology a thumbs up: “Using an electric field to accelerate ageing is a feasible way to shorten maturation times and improve the quality of young wine”. Who knows – maybe you’ll soon be drinking a wine that has been zapped?
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Staying warm: Cast iron vs. stainless steel

Thursday, March 1st, 2007

Cookware made from cast iron has a reputation for keeping food warm for a long time. Is that really true? Best way to find out is by an experiment. I decided to compare a cast iron pot with one of stainless steel. These are the pots I used:

cast-iron-stainless-steel.jpg

For the first experiment I filled them each with 2,5 L of water, put the lids on and brought both to the boil and let them boil for a minute so the pot itself would be warm throughout. Then both were placed on cork plates and left to cool. The temperature probe was carefully inserted under the lid in order to reduce the heat loss, and removed once the temperature had stabilized. For the second experiment 5 L of water were used. The measured temperatures are shown in the graph.

cooling-curve.jpg

Contrary to what I had expected, the stainless steel pot keeps water warmer! After approximately 1,5 hours there is a 10 °C difference between the two. As expected, when using 5 L of water, it stays warm longer. Physical data for the two pots are given in the following table:

Cast iron Stainless steel
Volume 6 L 6 L
Diameter 27,9 cm 25,0 cm
Height 11,5 cm 14,5 cm
Surface area
(top+sides)
1619 cm2 1629 cm2
Surface area
in contact with 5 L water
1301 cm2 1286 cm2
Weight 6,1 kg 2,3 kg
Wall thickness ~4 mm <1 mm
Heat capacity of pan 2,8 kJ/K 1,2 kJ/K
Thermal conductivity 80 Wm-1K-1 16 Wm-1K-1
Thermal diffusivity 22 x 10-6 m2/s 4.3 x 10-6 m2/s
Emissivity 0.95 0.07

The heat capacity of the cast iron pot is more than double that of the stainless steel pot. But this is negligible compared to the heat capacity of water: 10.5 kJ/K (2,5 L) and 20,9 kJ/K (5,0 L). Also, there is only a small difference in their surface area which cannot explain the large difference in temperature loss observed.

This leaves me with two eplanations:

  • Cast iron is better heat conductor and has a higer thermal diffusivity
  • Cast iron (being nearly black) has a much higher emissivity than a polished stainless steel surface. The reason for this is that absorption and reflection of radiation are related.
  • My guess is that the difference in emissivity is more important (but please correct me if I’m wrong). With an infrared thermometer, one should therefore be able to measure a difference between pots of cast iron and polished stainless steel (even though they’re at the same temperature!) due to the difference in emissivity. Any one who can do the experiment and report back?

    Conclusion: There are many good reasons to use cast iron, but keeping food warm is not one of them!