Why does overcooking food usually harden it?

That, and why does the overcooked / hardened food become bonded or firmly stuck to the cookware?

syfry said:

What causes overcooked food to harden at the molecular level?

The loss of water and volatile plasticizers.

syfry said:

TL;DR Summary: What causes overcooked food to harden at the molecular level?

That, and why does the overcooked / hardened food become bonded or firmly stuck to the cookware?

I don’t know about every food, but proteins (like egg whites) will unfold and start cross linking.

There are foods that soften with overcooking - long boiling or braising makes vegetables mushy and otherwise tough cuts of meat more chewable. In these cases the heat and moisture is breaking things down.

A casserole, covered with lid or foil to mitigate water-loss, generally improves given some extra time as the fibres and starch progressively break down to more digestible format.

I'm reminded that traditional 'Irish Stew' / 'Scouse' tastes much better the second day, as much of the root-veg starch has further time to hydrolyse...
And, yes, budget cuts of meat cook from edible to eatable...

Against that, I'd a clan of kin-folk who firmly believed all 'greens' should be cooked unto 'spreadable'...
"But what about the Vitamins--"
"Eat Your Greens !!"

Nik_2213 said:

A casserole, covered with lid or foil to mitigate water-loss, generally improves given some extra time as the fibres and starch progressively break down to more digestible format.

This is true but there seems to be a bit pradoxical. Most seafood is best cooked with very short times and the same applies to offal but slow cooking at low temperature will render most meat very tender. Biology is a complicated business.

Most seafood but not salmon. The fat content is probably why it is so forgiving. It's one of the reasons why we BBQ it for Thanksgiving instead of suffering with a dried out turkey. Even when I burn it or forget that it's on the grill too long it's still good. You can't do that with most fish.

In general food does not harden when overcooked. British cuisine largely relies upon that not being true.

Too much, of a good thing, is bad for you.
Likewise, "overcooking", is a truism, when the food becomes hard and sticks to the pan.
If you boil it too much, it simply becomes a soup.

This needs a dose of biochemistry (and basic chemistry) of pectin. Pectin holds plant cells together --middle lamella -- , so it is primarily responsible for the toughness level of unripened or uncooked fruit or stems or roots. See:

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

Plant biochemistry texts often spends many pages on the synthesis and degradation (ripening or cooking mostly) of the many isomers. Water is required for controlled degradation.

Moist heat tenderizes meat:

Collagen, a connective tissue, helps hold the muscle fibers in meat together. When cooked in the presence of moisture, collagen dissolves into gelatin, which allows the meat fibers to separate more easily. This is the essence of tenderizing tough cuts of meat.

Per Veratasium

Ok. So when all the moisture evaporates during cooking Meat proteins oxidize and turn black, other less damaged proteins make wonderful glue (example hide glue for animal hides). In general liquids derived from overcooked collagen, when dried, are hard to remove with water and detergent.

Plant cells have small amounts of proteins, which when degraded by high temp as a result of water loss, make "glue" mixed into the oxidized charcoal-like ash.

Burned fats make some really interesting toxins, like aldehydes, not glue necessarily....

jim mcnamara said:

This needs a dose of biochemistry (and basic chemistry) of pectin. Pectin holds plant cells together --middle lamella -- , so it is primarily responsible for the toughness level of unripened or uncooked fruit or stems or roots. See:

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

Plant biochemistry texts often spends many pages on the synthesis and degradation (ripening or cooking mostly) of the many isomers. Water is required for controlled degradation.

Moist heat tenderizes meat:

Per Veratasium

Ok. So when all the moisture evaporates during cooking Meat proteins oxidize and turn black, other less damaged proteins make wonderful glue (example hide glue for animal hides). In general liquids derived from overcooked collagen, when dried, are hard to remove with water and detergent.

Plant cells have small amounts of proteins, which when degraded by high temp as a result of water loss, make "glue" mixed into the oxidized charcoal-like ash.

Burned fats make some really interesting toxins, like aldehydes, not glue necessarily....

Interesting, so pectin probably makes a raw carrot hard, cooking softens the carrot, then burning the carrot will harden it again (but I'm still unclear as to how, molecularly).

Also...

Sounds like the cooking makes protein and collagen unusable for constructing biology. So I'm guessing our body's digestive systems have ways to reassemble the root parts of 'ruined' proteins back into fully functional protein for our body to use and to build stuff with.

Think of cooking as pre-digestion.

For our size, humans have relatively tiny teeth, and a small digestive tract.

Humans who cooked had a huge advantage over other primates in terms of killing food pathogens and parasites like tapeworms. Cooking kills of most bacteria, for example.

I'm not sure what a ruined protein is. Proteins are long chains of amino acids - there are 20 different amino acids (AA) that humans can use to "string" (polymerize) into a protein. 9 of these are essential amino acids. That means humans must get all of those 9 amino acids from food. Proteins that provide all of these AA's are called 'complete' proteins.

Mother's milk is an example. It contains the protein casein - a long AA chain. 212 AA's strung together.

Infants suckle. In less than five minutes all of the casein in the milk is broken down into short AA chains - polypeptides. In another few minutes most of the polypeptides are now single AA's. Anabolic (tissue building) processes "decide" to build new replacement tissues - skin collagens, muscle fibers, connective tissue. This anabolic switch gets turned on ONLY when the body senses a large enough dose of AA's:

a special group of branch chain AA's -isoleucine or leucine for example. These are in the list essential AA's

So the milk proteins are torn down to basic protein building blocks - AA's - then put back together into all-new proteins. If humans do not get those essential AA's over a period of time, the unused AA's can undergo gluconeogenesis - turning AA's into glucose. Or get flushed down the toilet in urine.

This is as close to 'ruined' proteins as I can get.

jim mcnamara said:

Think of cooking as pre-digestion.

For our size, humans have relatively tiny teeth, and a small digestive tract.

Humans who cooked had a huge advantage over other primates in terms of killing food pathogens and parasites like tapeworms. Cooking kills of most bacteria, for example.

Mother's milk is an example. It contains the protein casein - a long AA chain. 212 AA's strung together.

Infants suckle. In less than five minutes all of the casein in the milk is broken down into short AA chains - polypeptides. In another few minutes most of the polypeptides are now single AA's. Anabolic (tissue building) processes "decide" to build new replacement tissues - skin collagens, muscle fibers, connective tissue. This anabolic switch gets turned on ONLY when the body senses a large enough dose of AA's:

a special group of branch chain AA's -isoleucine or leucine for example. These are in the list essential AA's

So the milk proteins are torn down to basic protein building blocks - AA's - then put back together into all-new proteins. If humans do not get those essential AA's over a period of time, the unused AA's can undergo gluconeogenesis - turning AA's into glucose. Or get flushed down the toilet in urine.

This is as close to 'ruined' proteins as I can get.

Ah, the parts that had seemed like ruining of proteins were about how in meat, the proteins oxidize and turn black, while the other less damaged proteins make glue, and how heat degrades the plant proteins, but now after you've clarified how cooking is more like an early start to digestion, I'm seeing that ruined is probably the wrong wording for that.

Had no idea the body is breaking all the proteins down into their individual components for reuse. That now makes more sense since parts are more useful in a wider range of places than their whole or completed bondings.

Following that line of reasoning it's probably the same with animal fats we eat: break the animal fats into whatever we'd use to create our own body's human fats with.

syfry said:

Had no idea the body is breaking all the proteins down into their individual components for reuse. That now makes more sense since parts are more useful in a wider range of places than their whole or completed bondings.

The amino acid - Lego analogy.
There are twenty differently shaped pieces, nine of which are essential to construction. To obtain the blocks required to build a new structure, you must dismantle (cook) the structures that were previously built by others. Damage to some blocks (overcooking) during the deconstruction, wastes resources, and makes a new construction more difficult or impossible.

To be clear - yes 9 AA are essential. What that means is 11 AA's can be synthesized and turned into proteins.
Usually they are synthesized from a mix other AA's, some essential some not essential.

There is a good summary of human amino acid requirements here.
https://en.wikipedia.org/wiki/Essential_amino_acid

Baluncore said:

Damage to some blocks (overcooking) during the deconstruction, wastes resources,

Let's hear it for the Crackling on a roast pork joint. Naughty but nice.