Definition of substitution. 1  1a : the act, process, or result of substituting one thing for anotherb : replacement of one mathematical entity by another of equal value. 2  2 : one that is substituted for another.
Homogenized milk is any sort of milk that has been mechanically treated to ensure that it has a smooth, even consistency. The homogenization process typically involves high temperatures, agitation, and filtration, all aimed at breaking down milk's naturally occurring fat molecules.
Milk for dairy products and as human food is also obtained from camels, donkeys, sheep, yaks and goats. Milk is also sometimes homogenized to prevent the cream from separating from it and leaving a thinner residue. Buttermilk can also refer to fermented milk drinks particularly in countries with a warm climate. Whether buttermilk has been prepared by the traditional churning of milk or cultured, it has a tartness unlike milk due to the high lactic acid content produced by the bacteria during the fermenting process.