[CnD] FW: Scientific answer about foil

Debbra Piening debbra.piening at att.net
Thu Feb 2 20:36:30 GMT 2012

Here's what I got last year from the list.  Your guess is as good as mine.

-----Original Message-----
From: cookinginthedark-bounces at acbradio.org
[mailto:cookinginthedark-bounces at acbradio.org] On Behalf Of Seigenthaler
Sent: Friday, February 25, 2011 2:46 PM
To: cookinginthedark at acbradio.org
Subject: [CnD] Scientific answer about foil

When I googled this, I got two very different answers.  I'm going with the

1.  Take it from the people at Reynolds. They make the stuff. They will tell
you that it makes no difference which side is in or out. Optical light
scatters differently from the dull side than from the shiny side, which is
more like a mirror. But both sides absorb or reflect light (and infrared
radiation) equally.

2.  Answer below from:

The shiny side of foil is slightly better reflector of heat. Face that side
of the foil in the 
appropriate direction. To keep things cold, put the shiny side on the
outside -- that 
will reflect incoming heat. To keep things warm, face the shiny side inward
toward the 
hot food -- to reflect the heat that is trying to escape back into the food.

Note that people often bake potatoes with the shiny side out -- that is
because it makes 
for a better (prettier) presentation. In reality, baking them that way
reflects the 
incoming heat on the outside, slightly slowing the cooking process.

Radiative heating will happen by the absorption of infrared radiation (IR
radiation) or 
heat emanating from all around the food (within the BBQ).  Now please
consider infrared 
radiation to be in the wavelength range of 880 nanometers or so.  Realize
that this 
wavelength of "light" is very near the color red in the visible portion of
the spectrum. 
Further, this means that the radiation will act like light and the foil
shall act as a 
mirror.  Knowing now that you want to transmit (foil to absorb all
radiation) as much IR 
through the foil as possible.  It should be clear to you that the dull side
should be 
OUTWARD facing so as not to minimize the reflection of IR radiation.


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