Sad Science of Soup

[JoNorvelleWalker]

Soup is the title of a chapter in Herve This' book Kitchen Mysteries, which currently I am reading.  This essay asserts that blowing on soup cools it by disturbing the boundary layer of what is technically smoke (not vapor) above the hot liquid.  @nathanm reached essentially the same conclusion in Modernist Cuisine.

 

As much as I respect the great minds, I call balderdash.  I maintain blowing on soup cools it primarily by the Joule-Thomson effect, in which a gas is cooled by being forced through an orifice, eg. one's lips.  This is easy enough to prove with an experiment:  with mouth open, blow on soup with all one's might.  Keep blowing, because you will be at it quite a while.

 

Then purse your lips, as one naturally does when cooling soup, and continue blowing.  The soup cools quickly.  The experiment does not need soup, or even a thermometer.  With mouth open blow on your hand.  Your breath feels warm.  Purse your lips and continue blowing.  Your breath feels cool.

 

Thank me next time you don't scald your tongue.

 

[liuzhou]

I was sent to bed with no supper if my mother caught me blowing on my food! If I'd pee'd in my soup she wouldn't have been any more disgusted!

[Duvel]

On 9/5/2021 at 8:23 AM, JoNorvelleWalker said:

As much as I respect the great minds, I call balderdash.  I maintain blowing on soup cools it primarily by the Joule-Thomson effect, in which a gas is cooled by being forced through an orifice, eg. one's lips.  This is easy enough to prove with an experiment:  with mouth open, blow on soup with all one's might.  Keep blowing, because you will be at it quite a while.

 

As a rule of thumb, you'll achieve ~0.25 K/bar JTE when decompressing air. Assuming that you are unlikely able to create more than 0.1 bar overpressure in your mouth, that amounts for 0.025 K of temperature decrease when blowing. It is unlikely to cause a significant effect to soup.

 

On 9/5/2021 at 8:23 AM, JoNorvelleWalker said:

Then purse your lips, as one naturally does when cooling soup, and continue blowing.  The soup cools quickly.  The experiment does not need soup, or even a thermometer.  With mouth open blow on your hand.  Your breath feels warm.  Purse your lips and continue blowing.  Your breath feels cool.

 

Funny enough, the reason for that is that the superficial moisture on your hand gets evaporated faster by the stronger blow through your pursed lips. The heat of evaporation of water is magnitudes larger than the JTE ...

 

So, all in all, both guys seem to be in line with the current themodynamic theory ...

Edited June 9, 2022 by Duvel (log)

[weinoo]

I did both of these this morning, then I tried the soup to see.  The cold borscht didn't burn my tongue at all, and I plan on trying it on my cacik next.

[rotuts]

@Duvel 

 

Excellent dissertation .

 

it then occurred to me :

 

if the air cools down , after passing thought pursed lips

 

and expanding 

 

where does the thermal energy in there air go ?

 

as a rule :  thermodynamics suggests there is no free lunch.

 

if it's cooler in one spot , then it's hotter in another ?

 

does one's mouth heat up ?  The Compression step of the equation

 

Does one's saliva eventually boil ?

 

if done repeatedly ?  inquiring minds ( sic )  might want to know

 

or not .

 

or does one just pass out , due to the lowering of one's 

 

pCO2 before this can happen ? 

 

not a thermal experiment Id suggests for everyone .

 

 

Edited June 9, 2022 by rotuts (log)

[Duvel]

1 hour ago, rotuts said:

where does the thermal energy in there air go ?

 

as a rule :  thermodynamics suggests there is no free lunch.

That is completely correct, @rotuts.

 

What is happening here is that the entire process is insenthalpic, so the overall energy remains constant, yet within the gas there is a coversion of kinetic thermal energy (what we consider as temperature) and potential thermal energy (that is slightly more complex to put into a practical example). The best way to imagine this (at least this is how I ised to teach it) is that if the distance between the particles increaes, their potential energy increases (e.g. in an expansion process). If the overall thermal energy remains constant and the potential thermal energy increases due to expansion, the kinetic thermal energy needs to decrease which manifests itself as a decrease in temperature. I hope this helps a bit …

[rotuts]

@Duvel 

 

indeed it does !

 

esp after a glass of TJ's Table wine

 

w ice as its  warming up here.

 

so , in theory 

 

its possible to boil your own saliva ?

 

just a thought .

 

as Gilbert and Sullivan 

 

so succinctly posted out in 

 

HMS Pinafore 

 

https://en.wikipedia.org/wiki/H.M.S._Pinafore

 

https://www.youtube.com/watch?v=kBK39BKWuQg

 

sorry it you get the commercials

 

"  No Never ?  No never !  no never ?  well hardly ever "

 

this is the Second Law of Thermodynamics , right their !

 

Kudos to G & S , for ignoring 

 

Thermo ! and 3  , which might have involved 

 

French Horses ?

 

Edited June 9, 2022 by rotuts (log)

[Duvel]

23 minutes ago, rotuts said:

HMS Pinafore 

 

https://en.wikipedia.org/wiki/H.M.S._Pinafore

Funny enough I learned English (the spoken part at least) mostly during my university time (grinding over thermodynamics) watching The Simpsons (while drinking beer to enhance synaptic response). Therefore - as a side effect - I am also familiar with certain cultural aspects of the anglophone world (in short form, as long as the content was correctly transported by The Simpsons), such as the HMS Pinafore. Needless to say, while I enjoy your link the true version lies with Sideshow Bob …

 

 

(the “no never” part starts at 0:49)