In cooking, brining is a process similar to marination in which meat is soaked in a salt solution (the brine) before cooking.
Brining makes cooked meat moister by hydrating the cells of its muscle tissue before cooking, via the process of osmosis. The brine surrounding the cells has a higher concentration of salt than the fluid within the cells, but the cell fluid has a higher concentration of other solutes. This leads salt ions to enter the cell via diffusion. The increased salinity of the cell fluid causes the cell to absorb water from the brine via osmosis. The salt introduced into the cell also denatures its proteins. The proteins coagulate, forming a matrix which traps water molecules and holds them during cooking. This prevents the meat from drying out, or dehydrating.
In many foods the additional salt is also desirable as a preservative. Note that kosher meats are salted during the process of koshering so they should not be brined.
