A new stupid science question

[Rat]

This is probably one that should end up on the back page of New Scientist, but I thought maybe someone here might have an idea. If I make instant mashed potato (I know, but I'm sometimes too lazy to do it properly), the make we normally have involves adding the granules to the water, unlike Smash, which I think does it the other way round. I use one of two containers to do this. Sometimes I use a glass jug, probably of around a pint and a half, so it just fits in. This always works. Sometimes, though, I use a larger glass mixing bowl, of the sort you'd use to make up cake mix, about a foot across at the top.

When I use the latter, the mash turns out too wet and sloppy. What changes? The only variable I could think of was the time, in that I pour the water from the kettle into the jug, to measure it, then into the bowl, so there's maybe an extra ten seconds from the water boiling to adding the potato mix. So I tried measuring the water out into the kettle, and even warming the bowl, but the same effect occurs. The mix is from a whole sachet, so that's a constant, so as far as I can tell, the only difference is the size of the container.

Any ideas? Evaporation rates occur to me, but seem unlikely to have that much of an effect. Anyone want to try this at home to see if the same occurs normally? Just post the mash to me if you have ethical objections to eating it.

[andyandy]

maybe the larger surface area of the second container brings the temperature down to a less than optimum mixing temp?

[Rat]

I don't really know, though, how the mixing process works. I suppose I need to waste a packet trying to make it up with cold water. It presumably is absorption (or adsorption; I never really grasped the difference properly), as I think the granules are mainly just dried potato.

[skeptigirl]

There are lots of quick fix foods (my cooking expertise is in this field ;) ) that look cooked but need a little more time to thicken. Microwave noodle dishes are like that, cream of wheat of course and from the sound of it, your potatoes.

Flour (wheat starch), corn starch, and potato starch are all thickening agents. That means temperature and time will affect the change in their molecular structure which results in thickening.

So either it is the cooler temperature from the extra step and/or the greater heat loss from the wide mouth bowl, or you are mixing and stirring faster in the bigger bowl and just don't realize it or both.

Simple physics. :)

[joobz]

Hot water will penetrate the starch particles faster, making them swell more easily and thereby achieve a thick consistency sooner.

My guess is that your glass mixing bowl has more glass, and represents a bigger heat sink than the pitcher. (presuming we can ignore heat loss arround it, stagnant air is a poor conductor of heat). To test this hypothesis, make a batch with your mixing bowl preheated with hot tap water. pour out this water, pour in your boiling water and try the mix.

[skeptigirl]

And skeptigirl wins the race, joobz comes in a decent second. :D

But is it a structural change or mere water penetration? I believe the molecules actually change and bind with the water molecules.

Yes, I was correct. (http://www.lsbu.ac.uk/water/hysta.html)

"Of the two components of starch, amylose has the most useful functions as a hydrocolloid."

Hydrocolloid defined (http://www.thefreedictionary.com/hydrocolloid)

"a substance that forms a gel with water"

[joobz]

There are lots of quick fix foods (my cooking expertise is in this field ;) ) that look cooked but need a little more time to thicken. Microwave noodle dishes are like that, cream of wheat of course and from the sound of it, your potatoes.

Flour (wheat starch), corn starch, and potato starch are all thickening agents. That means temperature and time will affect the change in their molecular structure which results in thickening.

So either it is the cooler temperature from the extra step and/or the greater heat loss from the wide mouth bowl, or you are mixing and stirring faster in the bigger bowl and just don't realize it or both.

Simple physics. :)
It'd actually be a fun problem for a heat transfer class.

assume some starch swelling kinetics (with some ahrenius dependant kinetic constant) and have the heat transfer coefficents for the glass bowl. Top it with the mixing rate for the convective heat transfer to the bowl and the convective heat transfer from the surrounding atmosphere. We can even add in comparisons of forced air vs. stagnant.

[joobz]

And skeptigirl wins the race, joobz comes in a decent second. :D

But is it a structural change or mere water penetration? I believe the molecules actually change and bind with the water molecules.

Yes, I was correct. (http://www.lsbu.ac.uk/water/hysta.html)

"Of the two components of starch, amylose has the most useful functions as a hydrocolloid."

Hydrocolloid defined (http://www.thefreedictionary.com/hydrocolloid)

"a substance that forms a gel with water"
I bow to your speed.:D

Structural change and water swelling are identical in this sense. It is the water that plasticizes the starch molecules, forming the thicker solution. Starch is a polymer. Polymers in solution act like a bowl of spegetti. The larger the spegetti chains, the thicker the solution. But the water molecules interdigitate the chains allowing them to expand and flex, adopting more relaxed/expanded structures.

[skeptigirl]

Did you mean Arrhenius equation (http://en.wikipedia.org/wiki/Arrhenius_equation)?

I bow to your superior knowledge in physics. Mine in this case is limited to the gourmet specialty of microwave cooking. ;)

[joobz]

Did you mean Arrhenius equation (http://en.wikipedia.org/wiki/Arrhenius_equation)?

I bow to your superior knowledge in physics. Mine in this case is limited to the gourmet specialty of microwave cooking. ;)
and I bow to your suprior spelling :)

all this bowing is giving me back problems..

[skeptigirl]

Here you go, try this.

:chores035:

In the meantime, I do believe :solved2

[Ivor the Engineer]

While my dad was in hospital he could not swallow properly (Dysphagia) so all his drinks had to be thickened with this (http://www.dysphagia-diet.com/t&e_thickener.htm) colourless, tasteless powder. Perhaps it could help some of you get that perfect instant mash potato:D

Well, I’m off to Spain for a week. See ya’ll soon:)

[Dancing David]

Did you mean Arrhenius equation (http://en.wikipedia.org/wiki/Arrhenius_equation)?

I bow to your superior knowledge in physics. Mine in this case is limited to the gourmet specialty of microwave cooking. ;)

As someone who often prepares food for the less that patient younger members of the family, I also find that the oven and boiled water are essential.

Probably a whole thread in here somewhere. Which forum?

[Soapy Sam]

To thicken watery instant spud, sprinkle in a spoonful of porridge oats while stirring.
Rat- if I mix anything in a measuring jug, I use a whisk, to avoid sloshing. In a bowl, I'm apt to use a spoon or a fork. At work, where I mix rather a lot of polymers, I use high shear blenders and 75HP centrifugal pumps.
(Don't try this at home). The viscosity yield of any polymer (we'll include potato starch for simplicity) is mostly a function of concentration, pH, water hardness, salinity and shear rate. In your case , only shear rate is likely to vary much. I wonder if you mix harder in the bowl, but use a tool which actually blends less effectively? To complicate matters- the same tool may work better in a small vessel with higher initial turbulent mixing than in a larger vessel where fewer vortices form.

I know a rig with a 9 tank mud mixing system. It's impossible to mix polymers effectively in the largest tank, because the mix pump provides insufficient shear and cavitates like a bagpiper on Nitrox. Damn nuisance, actually.

[Myriad]

The only variable I could think of was the time, in that I pour the water from the kettle into the jug, to measure it, then into the bowl, so there's maybe an extra ten seconds from the water boiling to adding the potato mix. So I tried measuring the water out into the kettle, and even warming the bowl, but the same effect occurs. The mix is from a whole sachet, so that's a constant, so as far as I can tell, the only difference is the size of the container.

Any ideas? Evaporation rates occur to me, but seem unlikely to have that much of an effect. Anyone want to try this at home to see if the same occurs normally? Just post the mash to me if you have ethical objections to eating it.

I can think of another possible variable: the amount of agitation in the mixing process. When you mix the ingredients in a jug, you have the option of stirring gently, stirring vigorously, or even capping the jug and shaking the bejeesus out of it. When you mix them in a wide bowl, you're pretty much limited to stirring gently, unless you make use or the electric mixer the bowl came from, or you don't care whether or not it stays in the bowl.

When mixing up starch (long strands of hydrophilic molecules) with water, the amount and type of agitation, whether too little or too much, whether reaching all parts of the mixture or leaving some volumes under-mixed, would almost certainly affect to consistency of the result! (The presence of bejeesus, in particular, tends to make starch mixtures runny; if you shake it out of there you'll get a firmer consistency.)

Respectfully,
Myriad

[articulett]

It's kind of off topic, but here's a handy hint I learned from the Naked Scientists...(and it's probably obvious if you have experience)--but cling wrap clings much better to plastic bowls that metal bowls because metal bowls conduct the "static electricity" (at least, I think that was the explanation).--In any case, I can verify that cling wrap does, indeed, stick to glass (and ceramic) bowls with greater clinginess. Should you want to hasten the thickening of your mash, put them in a glass or ceramic bowl with cling wrap in the fridge.

(And skepticgirl--I appreciate your culinary explanation--)

[skeptigirl]

I think he wants to eat the instant Mash, well, instantly, articulett, so the fridge wouldn't be the place.

But it's an interesting explanation about why cling wrap clings or not. For parents of those kids still in grade school, what a great simple project for the science fair -> test the clinginess of plastic wrap on various surfaces and investigate the mechanics of it. You could have a microscope to see the surface texture or photos off the net on a display board along with the samples.

I thought it had to do with surface imperfections that allowed air in. The glass surfaces are much smoother than metal. But the static charge sounds like a more specific reason behind the phenomena.

[pchams]

gourmet specialty of microwave cooking

Isn't that an oxymoron? ;)

[articulett]

http://www.newscientist.com/article/mg15621059.000.html

The last word on cling wrap according to new scientist:

Question: Why doesn't cling film cling to a metal bowl as well as it does to an equally smooth glass or ceramic one?

Answer: Cling film, known as cling wrap in the US, works because it acquires an electric charge as it is peeled from the roll. It can then stick to an insulating body by the same mechanism that an uncharged piece of paper sticks to the charged glass of your computer or television screen.

The mechanism relies upon the cling film and the object to which it is sticking being at a substantially different electrical potential. This works when the object is an insulator. When the object is metal, the charge on the film is dissipated throughout the object, so negating the effect.

Old cling film taken off the roll doesn't work either. After a while, the charge breaks away, and the clingyness is lost.

[tkingdoll]

But can you recharge it by wrapping it round a cylindrical object then unpeeling it again?

[Rat]

Must remember not to ask questions when I'm not going to understand the answers. Thanks for answers anyway, all; I have some reading to do, and then I might understand it.

[Schneibster]

I have a theory, and it may or may not stand up to the test. My proposal is that since heat leaves by conduction, radiation, and convection, there is more than one difference between the jug and the bowl (at least with respect to the rate at which heat leaves the system). The first difference is the surface area of the mixed water and potato; the larger this surface area, not only the larger the radiation that can escape from it, but also the larger the area for air convection to occur. The second difference is the larger surface area of the inside of the bowl with respect to the jug; this gives more opportunity for conduction. A third possibility has to do with radiation out through the bowl, but that gets into the differences between the transparency to infrared radiation of the jug and bowl, and if they are the same material, then this is unimportant. Finally, the surface area by which the bowl radiates the heat may also be important, since the flow of heat is proportional to the temperature difference, and if the bowl has greater surface area, it can lose heat faster and therefore maintain a higher temperature difference with the mash, thus robbing heat from it faster.

My theory, therefore, is essentially that the difference between the "good" mash from the jug and the "less good" mash from the bowl is that the heat leaves the mash before its work is done in the bowl, but the jug keeps it hotter longer.

You could test this by:
1. Adding insulation to the outside of the bowl, in addition to warming it as suggested previously; and
2. Adding a cover to the bowl to slow radiation and convection losses from the surface of the mash.
If these two suggestions yield "better" mash, then you have essentially proven my theory.

Whether I would eat such a concoction is highly doubtful to say the least.

[skeptigirl]

Must remember not to ask questions when I'm not going to understand the answers. Thanks for answers anyway, all; I have some reading to do, and then I might understand it.
What don't you understand?

Here's the summary of evidence supported posts (leaving out the speculation).

Time and temperature are different just enough to make the potatoes appear to have more fluid in the wide mouth bowl. In a short time, they should thicken up as well.

The potato starch needs heat and time to cause the reaction which in cooking is referred to as "thickening". What is really happening is the water molecules and the starch molecules are combining in such a way as to form larger molecules.

The water is only loosely bound and additional heat can displace it from the starch again, but that's another topic. Anyway the starch water compound becomes gelled making your potatoes thicker.

Bottom line, there is a heat and/or time difference you just aren't noticing.