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Re: [Phys-L] physics and potatoes



An experimental physicist would want to run two similar potatoes side by side: one covered in aluminum foil and another covered in BLACK anodized aluminum foil.

This reminds me of the analysis that accompanies "pyramid power" examples of the "cookie Jar effect" when cookies last longer under a pyramid shaped cover than when left on an open counter.

Our analysis is so sorely lacking in data points that we would flunk our students for submitting this discussion as their lab experiment?

FYI, microwave cooked potatoes do not have the same texture as oven baked potatoes. Maybe its the moisture retention of foil which keeps oven baked potatoes flakier. I try to NOT serve microwave potatoes to my friends.



Quoting John Denker <jsd@av8n.com>:

On 01/13/2015 04:53 AM, Anthony Lapinski wrote:

Here's Hewitt's answer from the Instructor's Manual:

The main reason for serving potatoes wrapped in aluminum foil
is to increase the time that the potatoes remain hot after being
removed from the oven. Heat transfer by radiation is minimized
as radiation from the potatoes is internally reflected, and heat
transfer by convection is minimized as circulating air cannot make
contact with the shielded potatoes.

In this example, as in so many others, Hewitt conducts a master
class in faulty reasoning.

The physics argument here is an example of what we call a
/category error/. The defining property is that the answer
would make sense if we were talking about something else.
Specifically, Hewitt's answer would (almost) make sense if
people wrapped potatoes /after/ cooking. Conversely, when
applied to potatoes in the oven, Hewitt's arguments "prove"
that foil serves to maximize the cooking time ... which
nobody would tolerate.

This is on top of the even more fundamental mistake of asking
"why" without bothering to ask "whether".

It also fails the basic grade-school requirement to CHECK
THE WORK. For starters, we should ask: Do people wrap
other things (such as steaks) in foil when they come out
of the oven, to "increase the time that they remain hot"?
If not, what's special about potatoes that calls for such
treatment?

The foil also serves to retain moisture.

Well, finally, that part of the answer contains a bit of
correct physics. It is still sloppy reasoning because it
fails to consider simpler and better ways of achieving the
same objective.

On 01/12/2015 08:31 PM, I wrote:

[Grandmother] cut the end of the ham because her roaster
was too small to cook it in one piece.

In case anybody missed the point of the joke:

In addition to lacking a ham-sized roasting pan, Grandmother
also lacked a microwave oven.

Microwaves have been ubiquitous in restaurants since the
1970s. Any chef with the least bit of sense would just
microwave the potatoes. It's hard to think of any food
better suited to microwaving.

Microwaves have been ubiquitous in homes since the 1990s.

Furthermore, even the joke doesn't explain the foil phenomenon.
Microwaves or the lack thereof is not an explanation. That's
because before microwaves, anybody who wanted a better result
in a fraction of the time -- with less effort, less energy,
and less wasted aluminum -- would /steam/ the potatoes in a
vegetable steamer, and then move them to the oven (or broiler)
for a few minutes. This guarantees they get cooked evenly
and gives you good control of how crispy the skin gets.
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