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Author Topic: Why does porridge get thicker when you heat it?  (Read 9652 times)

Offline chris

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Why does porridge get thicker when you heat it?
« on: 02/04/2010 23:05:31 »
I was asked this on the radio the other day and I'm not sure I know a good quality answer, so I'd appreciate the opinion of everyone here.

Oats are starch, and the same thing happens with cornflour (also starch) when this is cooked, so this effect must be a manifestation of starch.

So what's going on when starch is cooked to make it become much more viscous?

Presumably the particles hydrate and increase in size, but why should this make them stickier?

Chris


 

Offline RD

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Why does porridge get thicker when you heat it?
« Reply #1 on: 03/04/2010 03:54:25 »
I was tempted to say Gluten ...

Quote
Glutenin is responsible for the firmness of dough in baking bread because it increases the stability through a 3-dimensional network that forms when sulfur cross-linkages develop between protein molecules during the kneading process
http://en.wikipedia.org/wiki/Glutenin


But oats (porridge) don't have gluten ...

Quote
Oat is the only cereal containing a globulin  or legume-like protein, avenalin, as the major (80%) storage protein.  Globulins are characterized by solubility in dilute saline. The more typical cereal proteins, such as gluten and zein, are prolamines (prolamins). The minor protein of oat is a prolamine; avenin.
http://en.wikipedia.org/wiki/Oat#Protein

But protein could still be the cause of sticky porridge rather than carbohydrate (starch).
« Last Edit: 03/04/2010 04:00:57 by RD »
 

Offline chris

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Why does porridge get thicker when you heat it?
« Reply #2 on: 10/04/2010 09:38:46 »
I've been poking about on the net and I actually cannot find a good answer to why starch thickens things when it cooks i.e. why adding cornflour to gravy makes it thicker.

Does anyone have any ideas about this?

Chris
 

Offline RD

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Why does porridge get thicker when you heat it?
« Reply #3 on: 10/04/2010 11:18:09 »
I've had another look ...

Quote
Starch gelatinization is a process that breaks down the intermolecular bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites (the hydroxyl hydrogen and oxygen) to engage more water. Penetration of water increases randomness in the general structure and decreases the number and size of crystalline  regions. Crystalline regions do not allow water entry. Heat causes such regions to be diffused, so that the chains begin to separate into an amorphous form. This process is used in cooking to make roux sauce, pastry, custard or popcorn.

Gelatinization is also known as the thickening of a liquid. The starch grains/flour granules absorb the liquid. When heated the grains/granules swelling and then burst, releasing starch into the liquid.
http://en.wikipedia.org/wiki/Starch_gelatinization

Somewhat confusing in that "Starch gelatinization" does not involve gelatin (which is a protein).
 

Offline hazel.rockbox

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Re: Why does porridge get thicker when you heat it?
« Reply #4 on: 04/03/2015 13:06:32 »
I've just come to this thread after trying to work out which bit of an oat makes porridge get thicker. This morning I put 1 teaspoon of my test subject into 3 tablespoons of water then microwaved them for 1 minute. I tested ground up whole porridge oats, oat bran and oat fibre made from oat husks. The whole porridge oats formed thick porridge, the oat bran went sticky and a bit thicker, and the oat fibre slightly darkened in colour but was otherwise unchanged by either adding to water or heating. Anyone know what oat husk is made from? Is it starch? Is it cellulose? And would that make it soluble or insoluble fibre (I'm assuming insoluble as it just sunk to the bottom of the glass).

Anyway, I also wondered why both cornflour and oats got thicker when heated in water and found this on Science of Cooking: "People often wonder what the difference is between cornstarch and flour. Both are cereal starches, but cornstarch is pure starch while flour contains gluten. The gluten reduces the thickening power of flour. One tablespoon of cornstarch thickens one cup (250 mL) of liquid to a medium consistency. It takes two tablespoons of flour—twice as much—to thicken the same amount of liquid."

This would suggest it is the starch that makes porridge thicker and that any proteins in it would actually inhibit the process. Any thoughts on this?
 

Offline Colin2B

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Re: Why does porridge get thicker when you heat it?
« Reply #5 on: 04/03/2015 16:36:48 »
Somewhat confusing in that "Starch gelatinization" does not involve gelatin (which is a protein).
Gluntinous just means  gluey, sticky, gummy.

I think the quote you give is the answer, the starch thickens as described.
 

Offline wolfekeeper

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Re: Why does porridge get thicker when you heat it?
« Reply #6 on: 04/03/2015 17:30:20 »
AFAIK both proteins and carbohydrates can gel; in eggs the proteins gel when the egg is cooked.

The basic process is polymerisation, a matrix forms that thickens the liquid and stops it moving as easily
 

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Re: Why does porridge get thicker when you heat it?
« Reply #6 on: 04/03/2015 17:30:20 »

 

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