Marinades were formerly used as a technique to preserve foods.
Any type of meat, whether it be beef, chicken, or fish would be submerged in a salty soup that was used to preserve the meat, due to the lack of a cooling system.
The last few hundred years, marinades are not only used to preserve meats but also to add flavor to them.
When we marinate, we think about saturating the meat in the rich tasting mixture of herbs, spices, salt,, vinegar, and oil (fat), with the purpose of infusing the meat with flavor.
This however is a MYTH.
Read More Here About Herbs and Spices
It is physically impossible for a marinade to penetrate deep into the meat. Most flavor molecules are to big to enter the muscle tissue cells of meat.
The tissue cells are about 75% water and tightly packed like a sodden sponge.
Oil molecules, which dispense most of the flavor molecules are also unable to enter the tissue cells.
This means, the the flavor of the marinade can infuse the meat no further than a few millimeters, leaving most it to pool on the surface.
Tender and Delicious Marinated Meat
The ingredients in marinades work together to enhance the flavor of meat and tenderize its outer layers.
While cooking the meat, sugars and proteins found in a marinade help to brown the meats surface, and creating a crisp, flavorful crust.
Keep in mind though, when adding an acidic ingredient like lemon juice, wine or vinegar, can slow the browning process.