Ask A Scientist: Denaturing Stuff

unprofessional cookery

Question:  “Is ceviche just pickled fish?  Could you call a pickle ‘vegetable ceviche’?”  -Makala O.  Corvallis, OR

Answer:  Ceviche, a South American dish consisting of fish and vegetables “cooked” with an acid, most certainly looks like a pickle but it couldn’t be further from one.Although it may look pickle like, from a chemist’s standpoint comparing ceviche and pickles are like trying to find the relation between a cat and a Buick.  Ceviche is made by modifying a protein’s structure through a process called denaturing.  Pickling, on the other hand, would preserve the protein.

See?  Cat and a Buick.  It really just boils down to organic chemistry.  Lets see why!

When you denature a protein, you change its physical structure by putting an external stressor upon it.  The external stress may be a strong acid, a base, an inorganic salt, or heat.  Ceviche is a great pescatarian version of this- as when the acid marinades with the fish, the flesh becomes much firmer than in its natural state.  Cooked eggs are also a great example of denaturing for vegetarians.  As the eggs started off as a viscous liquid, they’re magically changed into a solid structure when they’re put into a hot pan (preferably with copious amounts of butter).

But, you may ask, why can you denature an egg or some fish with some heat or some acid but cooking a vegetable or coating it with that same stuff isn’t the same thing?

Simple.  Vegetables are mostly composed of carbohydrates, and carbohydrates don’t denature.  Of course this is a sweeping statement, but for the most part there isn’t a way to physically change a vegetable using lemon juice.  Instead, the transformation seen when pickling or cooking carbohydrates happens because it’s a chemical change.

Lets put it this way.  If you put a lime into a brine of salt and vinegar then walk away, what happens?   Nothing.  When you come back to it, you will still have that same lime- just with a longer shelf life and extra flavor.  It won’t be soup or another fruit entirely.  To get that lime to be something completely different, like a pie, you would have to squeeze it and cook it with something else to form new chemical bonds.  The end result isn’t a lime in a pie shell, it’s a beautiful key lime pie

I know. It seems vague as that ceviche probably looks pretty much the same as that hypothetical pie when I describe it as such, but trust me, it’s a chemical change rather than a physical one.

Lastly, as mentioned before, denaturing changes the structure of a protein but it doesn’t preserve it.  If you cook an egg, it won’t be shelf stable indefinitely.  Eventually you’ll have a moldy, mummified egg.  Likewise, if you coat that seafood in lime juice and then leave it out poolside all afternoon, it’s entirely possible that you will end up with an indelicate gastric situation if you eat it later on.  Pickles, on the other hand, can sit on a shelf until you are ready for them or out in the blazing sun all day without giving you the trots.  This is because the acids and salts in the pickling process help preserve the integrity of the food rather than just modify it.

Isn’t science deliciously confusing?  I thought so.

By Hannah Nordgren, Science Enthusiast

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