Soft cheese is unripened cheese, while hard cheese has had time to ripen. The more ripe the cheese, the harder it is. Soft cheese is made by coagulating milk proteins, called casein, with acid. Hard cheeses are made with casein as well but are combined with enzymes and culture acids, and they are ripened with mold or bacteria.
The aging, or ripening, process for cheese depletes it of moisture. The longer a cheese ages, the drier it becomes. Hard cheeses keep longer than soft cheese because it's harder for bacteria to grow in drier places like hard cheese than in wetter places like soft cheese.
Soft cheeses are done before curd processing begins and after curdling is done. Salt is added, then these soft cheeses are ready for consumption. Curd processing begins with heating the curd to draw out whey from the cut curd. Salt is added afterwards, not only to enhance flavor but also to draw out more moisture and preserve the cheese from spoiling.
Cheeses are also categorized as semisoft or semihard. Semisoft cheeses include havarti, Gouda and Jack. An example of a semihard cheese is cheddar. Brie, ricotta and Camembert are categorized as soft cheeses, while Asiago, Parmesan and Mimolette are known as hard cheeses. These are good for grating.