Proteins. pH. Electrical charges. And when acids make marinated meat leathery.
Marinating makes meat taste yummier when cooked. Many recipes call for the use of acidic elements such as lime and lemon, as these supposedly help to tenderize the meat.
According to Cook’s Illustrated at Harvard, we should be careful about not making the marinade too acidic. And if we do use an acidic marinade, minimize the time meat is exposed to it.
The simple explanation has to do with pH and electrical charges. Proteins have a coiled structure with a mix of the latter. When there are either more positive or negative charges, the protein molecules repel one another. Space is thus created between the molecules, and fluid fills this space.
When a marinade is too acidic, the acids denature the proteins, and the coiled structure unravels. Typically, this is because the acids’ H+ ions break the hydrogen bonds in the proteins. When proteins denature like this, there may no longer be an excess of positive or negative electrical charges. There may be an equal number of both, and positive and negative charges cancel each other out.
As a result, the protein molecules no longer repel one another but instead draw closer to one another. This squeezes out the fluid that was in between, and the meat becomes less juicy, turning tough and dry like a piece of leather.
The pH at which all this happens is 5.2. It is also called the isoelectric point. That is why Cook’s Illustrated at Harvard prefers marinades with salt, and when it comes to acid, they avoid exposing meat to too much of it or for too long.
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