Fried round potato slices' shape....

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Sorry if already asked:
Why round, thin, fried potatos often comes out with a "saddle" shape?
Thanks.

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[A.T.]

Why round, thin, fried potatos often comes out with a "saddle" shape?

A deformation into a saddle indicates that the center has contracted (more than the periphery). Or that the periphery has expanded (more than the center).

 

[lightarrow]

A deformation into a saddle indicates that the center has contracted (more than the periphery). Or that the periphery has expanded (more than the center).

Can you help me understand it?
Thanks

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[phinds]

Slight differences in density/composition from one side to the other and/or differences in applied heat. If you are talking about deep-frying then the applied heat should not vary much so it must be density/composition. Your question is very vague so it's hard to arrive at a meaningful answer.

 

[itfitmewelltoo]

Can you help me understand it?
Thanks

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Yeah, like why not a dome? How do the areas and circumferences relate between shapes? I believe it has something to do with efficiency being greatest for the circle. More area can be added but not less, without holes. So, if say you keep the circumfernce the same and decrease the area, it has to bend. If you increase the circumference and hold the area it has to bend. Nature likes circles.

Cooking it changes that efficiency.

 

[Mark44]

Sorry if already asked:
Why round, thin, fried potatos often comes out with a "saddle" shape?

My best guess: When they are fried, heat is applied to one side of the potato slice, which causes that side to contract.

The heat removes water, causing the heated side to shrink, rising in the middle. If you flip them over, heat is applies only to the center of the slice, not to the whole slice like when they were put into the frying pan.

 

[A.T.]

Can you help me understand it?

Yeah, like why not a dome? How do the areas and circumferences relate between shapes?

Look up negative vs. positive curvature.

 

[OmCheeto]

Sorry if already asked:
Why round, thin, fried potatos often comes out with a "saddle" shape?
Thanks.

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Being somewhat lazy, I just googled it:

http://julea218.blogspot.com/2009/12/why-do-potato-chips-curl.html
Friday, December 11, 2009

[Question] why do potato chips curl?=)

[Answer]i read the answer from reader's digest..=)

potatoes are composed mostly of starch and cutting the potatoes in thin slices before frying them, makes the outer portion which has the less starch(less solid part) curl, because the moisture in the outer portion evaporates when frying them in oil..=)​

enjoy eating potato chips!=)​

Since I wasn't sure if "Reader's Digest" was a proper peer reviewed journal, I of course went to wiki to find out what "starch" was.

There I discovered, again, my almost complete and utter lack of knowledge of biological terminology.
But their "Potato" entry did list something about "starch":

https://en.wikipedia.org/wiki/Potato#Nutrition

Raw potato is 79% water, 17% carbohydrates (88% of which is starch), 2% protein, ...​

and their "Starch" entry gave a clue, but not an answer:

https://en.wikipedia.org/wiki/Starch

Melting point: decomposes​

Currently doing potato chip science in my oven.
I know you said "fried", but as a general rule, I don't fry things.

A deformation into a saddle indicates that the center has contracted (more than the periphery). Or that the periphery has expanded (more than the center).

I suspect you are correct.ps. My "French Fries" science experiment from last week was a total disaster. I can only describe the results as "shoe leather".
pps. My current experiment appears to be another total disaster, as nothing is curling. But from my previous culinary experiments, potato chips are always delightfully edible, as long as they don't turn black.
ppps. I suspect my slices are too thick.
pppps. Back to the drawing/cutting board...

 

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Thanks to every one who answered me.

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[OmCheeto]

My best guess: When they are fried, heat is applied to one side of the potato slice, which causes that side to contract.

The heat removes water, causing the heated side to shrink, rising in the middle. If you flip them over, heat is applies only to the center of the slice, not to the whole slice like when they were put into the frying pan.

I now suspect that this is closer to the answer than A.T.'s answer, as my potato peeler thickness chips also did not curl in the oven.
Though, it might be a combination of both.

But then again, after watching this video:



There are a lot of things going on, that I didn't know were involved in "properly" making potato chips.
And obviously, things I didn't know happened.
The chips initially sink, and then start to float once the water in the chips starts boiling.

And I believe soaking them in salt water removes some of the moisture.
What would happen if you soaked them for 24 hours, instead of 30 minutes?
Would the deep fried chips be curvier, or less curvy?

 

[sophiecentaur]

A deformation into a saddle indicates that the center has contracted (more than the periphery). Or that the periphery has expanded (more than the center).

That is good - as far as it goes. But then we also find an opposite curvature (across the 'minor axis) in many chips. That could be due later to tension in the central part which is supported more by the crisper, harder edge which can still rotate a bit and allow the tension in the longer major axis to give a small amount of opposite curvature.
I must now go and open a packet to check on the shapes. It's about lunch time!

 

[A.T.]

But then we also find an opposite curvature (across the 'minor axis)...

Not sure what you mean. Intrinsic curvature (saddle vs. sphere) is based on both axes. Opposite extrinsic curvatures of the two axes is what defines negative curvature (saddle).

 

[Dr. Courtney]

I think an experiment is in order to determine if the saddle shape that emerges depends more on the orientation as relates to the potato from which they were cut or from the orientation as they are lowered into the oil.

 

[sophiecentaur]

Not sure what you mean. Intrinsic curvature (saddle vs. sphere) is based on both axes. Opposite extrinsic curvatures of the two axes is what defines negative curvature (saddle).

The take a disc and curl it up. There need be only one axis of curvature as there is no area distortion. A saddle, I would have said, has curvature on another axis as well.
PS Your post make more sense to me after a third reading.

 

[A.T.]

There need be only one axis of curvature as there is no area distortion.

Converting a flat disc into a saddle requires area distortion. A saddle has negative intrinsic curvature.

A saddle, I would have said, has curvature on another axis as well.

The negative intrinsic curvature already captures that:
https://en.wikipedia.org/wiki/Gaussian_curvature#Informal_definition

 

[lightarrow]

Converting a flat disc into a saddle requires area distortion. A saddle has negative intrinsic curvature.

Ok. And (think) I got why (possible explanation) a contraction of the centre or an expansion of the outer part makes it in a saddle shape: if we draw in the disk's outer part a circle centred in the disk' centre, it has a greater length than one drawn near the inner part, is it right?

Now I have to get this. Let's say the greatest curvatures (in absolute sense) are along the x and y-axis and that the first is positive and the second is negative (according to some coordinate system). The question is: what physically made the disk/potato curl positively along x and negatively along y instead of the opposite? And why just x (and y) and not another couple of (necessarily orthogonal?) axis?
Is it just a matter of chance?

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[jbriggs444]

Let's say the greatest curvatures (in absolute sense) are along the x and y-axis and that the first is positive and the second is negative (according to some coordinate system). The question is: what physically made the disk/potato curl positively along x and negatively along y instead of the opposite? And why just x (and y) and not another couple of (necessarily orthogonal?) axis?

The "absolute sense" that you speak of would be extrinsic curvature -- curvature of the two dimensional shape based on its embedding in a three dimensional Euclidean geometry. This is the sort of curvature you get if you roll a piece of paper up into a tube.

No self respecting topologist would be caught dead using the term absolute to describe extrinsic curvature. Instead, extrinsic curvature would be better termed relative. It is curvature relative to an embedding.

The other sort of curvature is intrinsic curvature -- curvature that a hypothetical ant walking on the surface of the potato chip could measure by carefully counting his steps. For example, the length of a path around the edge of a potato chip (its circumference) is larger than pi times the length of a path through the center (its diameter). That's negative curvature. By contrast, a hemisphere has positive curvature. The length of a path around the rim of a hemisphere is shorter than pi times the length of a path from rim to rim through the center. [This is a bit hand-wavy. One has to nail down additional details to arrive at a rigorous measurement procedure for intrinsic curvature]

Rule of thumb is that if you can flatten a shape out without wrinkling, tearing or stretching it, then any pre-existing curvature was extrinsic. If you cannot flatten it out without wrinkling, tearing or stretching then the pre-existing curvature was intrinsic.Since the choice of x and y axes is arbitrary and can be made at random (as are the conventions for "upward" and "downward"), the chance that the potato chip has upward or downward extrinsic curvature about the x-axis is indeed random.

 

[A.T.]

And why just x (and y) and not another couple of (necessarily orthogonal?) axis?

In real life you always have some inhomogeneity (of the material and the external conditions), that determines which part folds which way.

 

[lightarrow]

The "absolute sense" that you speak of would be extrinsic curvature -- curvature of the two dimensional shape based on its embedding in a three dimensional Euclidean geometry. This is the sort of curvature you get if you roll a piece of paper up into a tube.

No, I was referring to the sign: with "absolute sense" I intended "absolute value", since one is positive and the other negative; sorry for the bad english.

. No self respecting topologist would be caught dead using the term absolute to describe extrinsic curvature. Instead, extrinsic curvature would be better termed relative. It is curvature relative to an embedding.

The other sort of curvature is intrinsic curvature -- curvature that a hypothetical ant walking on the surface of the potato chip could measure by carefully counting his steps. For example, the length of a path around the edge of a potato chip (its circumference) is larger than pi times the length of a path through the center (its diameter). That's negative curvature. By contrast, a hemisphere has positive curvature. The length of a path around the rim of a hemisphere is shorter than pi times the length of a path from rim to rim through the center. [This is a bit hand-wavy. One has to nail down additional details to arrive at a rigorous measurement procedure for intrinsic curvature]

Rule of thumb is that if you can flatten a shape out without wrinkling, tearing or stretching it, then any pre-existing curvature was extrinsic. If you cannot flatten it out without wrinkling, tearing or stretching then the pre-existing curvature was intrinsic.Since the choice of x and y axes is arbitrary and can be made at random (as are the conventions for "upward" and "downward"), the chance that the potato chip has upward or downward extrinsic curvature about the x-axis is indeed random.

Thanks.

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[lightarrow]

In real life you always have some inhomogeneity (of the material and the external conditions), that determines which part folds which way.

Thanks.

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