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Re: [Phys-L] physics and potatoes



Bernard's answer is the correct one. I worked in a restaurant kitchen before studying physics. My sister is a professional caterer and owned a restaurant and bar. Her husband managed a large and popular restaurant. 
Perhaps only Arlyn DeBruyckere and I have worked in a restaurant kitchen?
Potatoes are cooked in-bulk bare or oiled in very hot ovens. Even so, they take a long time to cook, more than an hour, which means they have to be prepped in advance and can't be made to order. You could try to time output, but luckily you don't have to. They stay hot for a long time right bare out of the oven and in foil for hours. 
Of course, making them in advance means that you have to make too many potatoes every night, but potatoes are cheap and it's no big loss. They have other uses, but leftover potatoes do often end up in the trash or in the hands of the homeless.
TL;DR: Foil keeps potatoes hot for a long time, and, arguably, looks pretty. 
Why not do this for everything? Well, I mentioned that it keeps potatoes for a long time, but it degrades their quality. Many people like crispy skins, and the trapped steam makes the skins soggy. You can perk them up with a quick visit to the salamander (a flame filled oven) or a torch. That's what some fancy places do.
Other things suffer even more by long holding times, even in foil. For example, steaks lose their flavor and surface crunch. On the other hand, steaks are far faster to cook than potatoes, so it isn't a big deal to wait.

But there is a way to holds steaks for a long time too. Sous vide cooking works like a charm. In this technique a steak (among other things) is placed into a sealed bag where the air has been removed. The bag is placed into a temperature controlled water bath that is the same temperature as final temperature that you'd like the steak to have. I like my steaks with an internal temperature of 130 F, so I make the water bath 130 F. It takes about an hour for the internal temperature of the steak to get to 130 F, but once it does, it can stay there indefinitely without overcooking.

When you are ready to serve, you remove the steaks from the bath and use a torch to brown the steak, taking just a couple of minutes.

Why don't fancy, fancy restaurants serve their potatoes in foil? A couple of reasons, only a few having to do with physics. First, they want to distinguish themselves from Sizzler's so they remove the foil. Second, some also believe that everything on the plate should be edible. Third, they often use special humidity and temperature-controlled holding trays so they don't need the foil. Fourth, some cook potatoes all night so that fresh ones are always getting done.

Zeke KossoverExploratorium


From: Bernard Cleyet <bernard@cleyet.org>
To: Phys-L@Phys-L.org
Cc: Nancy Seese <nancyseese@redshift.com>
Sent: Tuesday, January 13, 2015 11:46 AM
Subject: Re: [Phys-L] physics and potatoes


On 2015, Jan 13, , at 09:51, John Denker <jsd@av8n.com> wrote:

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?

I’m not an expert on this, because I v. rarely eat mammal flesh. 

However, I suspect flesh doesn’t keep, but cooked potatoes especially if wrapped, do.  This is indeed fortunate, as I suspect meat is cooked quickly while roasting potatoes is not.  So potatoes are treated as is fast fud, i.e. ready and waiting.

bc


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