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JohnD

Another one for the Sideways U. Common Room

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Not sure if this is for the Chemistry, Physics or Biology Faculties, I'l let you fight it out.

Just spent weekend with Grandsons One and Three, 6 years and 6 months old respectively, and this relates to No.1, who has a "Science Set" to play with.   Some test tubes, a flask, a beaker, a safety pipette, some safety specs and some, to be honest, rather boring "experiments".     We tried the one that seeks to put a shine on one of a couple of old pennies, in either water or lemon juice, but Mum had no lemon juice so I suggested vinegar.     After twenty minutes the pennies were not discernably different, and No.1 was bored, so decided to do his own 'tests'.      He had fun diluting milk with water, addding the milk with the pipette and making swirls in the mixture, that quickly blended.   But then we added some vinegar, titrating it in with the pipette.

Suddenly, the milk curdled!    OK, I knew why, the proteins were damaged by the acidity, and coagulated, but he was delighted by the 'snow globe' apperance in the flask, as small then large 'snowflakes'  in clear liquid appeared in what had previously been an opague suspension.     We played with this for a while, and he added 'hot' water, to no effect, but it was only hot tap water, so I suggested some boiling water.       This had a remarkable effect.     All the curds, previously settling out if left, as they were more dense than acidfied water, rose to the surface!   They stayed there until the water began to cool.

My question is, what can this dramatic 'experiment' show us?     I can try to explain protein coagulation to a 6 year old, but I have no idea why the curds became lighter.    Any explanations?

JOhn

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no but coke a cola would have cleaned the coins along with taking the enamel off his teeth(so they tell me! can not stand the stuff unless it has lots of Bacardi in it!)

Roger

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Absolutely true about sweet drinks contributing to the obesity and cavity epidemics, but it's the phosphoric acid (a 'permitted food additive"!) in Coke , that gives it is its 'bite' (! see what I did there?)  and if left long enough will clean dirty coins.   But wth only 0.6% (or something else very small) of the acid in Coke that is a very long time, like at least 24 hours.

These 'science kits' are supposed to help the kids learn something.    GS No.1 showed great promise by his enquiring mind, and I can try to explain but protein structure is bit much for a 6 year old, let alone coagulation.  I mean for goodness sake, you have to start with the structure of amino acids!  It's how the curds float in hot water that I can't understand myself!

JOhn

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This got me thinking about cheese, and there is something like this involved in some kinds of cheese making.  I'm far from an expert but I managed to find this, although as to why it happens I've no idea :)

Quote

Note: Curds washed in cold water will cause the water to flow into the curd and is just the opposite of adding warmer water to curds. This causes the moisture to flow out and thus drying the curd as in the process of making Gouda cheese.

https://cheesemaking.com/pages/cottage-cheese-recipe-dry-curd-instructions

When I was a kid my chemistry set was full of all kinds of stuff as a result of my father being a pharmacist, but I'm fairly sure that even the things it came with 'out of the box' wouldn't be allowed now.  I'm not sure I'd have trusted 7 or 8 year old me with a 'bunsen burner'  made out of a bottle, a shoelace and fuelled by methylated spirits...

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Thank you, Richy!    "Curds washed in cold water will cause the water to flow into the curd and is just the opposite of adding warmer water to curds."   That would explain the observation, even if not the mechanism.       I'll explore that!

Paul,

Yes, hmmmmmmmmmm, today!       But I've digressed before about the lavatorial nature of so many games offered to kids today - "Catch a poo" , "Fish for Floaters", even "Poo Head"

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A (very brief) foray down that particular fetid road brings up this, which proudly announces that it is "... handmade in Los Angeles."

Handmade..?

Time to get back to curdling milk.

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Hi John,

I'm sure that the curd would  have a certain amount of air in it.  The hot water would make it expand and allow the curd to float.

 

Roger.

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4 hours ago, RogerH said:

Hi John,

I'm sure that the curd would  have a certain amount of air in it.  The hot water would make it expand and allow the curd to float.

 

Roger.

Sounds good to me. If so pressurising the mixture should make them sink again. 

===

Remember the cornflake submarines that sank and rose after dosing with baking powder ?

Peter

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Why would it have air in it?     The curds are composed of proteins that have coagulated.   The liquor was stirred not shaken (!) so no airation by agitation.

Could there have been some gas released from the coagulation?  Certainly the rise when heated and fall when they cooled off makes this a convincing theorum.

But we didn't compress them, Peter.  Just left them to cool.

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11 minutes ago, JohnD said:

Why would it have air in it?     The curds are composed of proteins that have coagulated.   The liquor was stirred not shaken (!) so no airation by agitation.

Could there have been some gas released from the coagulation?  Certainly the rise when heated and fall when they cooled off makes this a convincing theorum.

But we didn't compress them, Peter.  Just left them to cool.

John, compressing them would be the test for gas bubbles Peter

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