What exactly is cheese and what makes different cheeses so, well, different?
The American Cheese Society offers a good explanation of how cheese is made and the definitions of farmstead and artisan cheeses.
"Cheese is a rather general term describing curdled milk (or cream). To curdle milk means to separate the whey from the curds. Milk proteins (casein) are ostensibly broken in half. One half precipitates out of the milk, becoming a solid (the curds). The other half remains liquid (the whey), though it ceases to be white. Milk can be curdled either by acid and/or by rennet. To be considered a true cheese (e.g. cheddar, swiss, brie, et. al.), acid AND rennet coagulation (i.e. curdling) is required.
First, a culture is added to the milk (or is already present in the milk in the case of some raw milk cheeses). This culture "ferments" the milk. Then, rennet is added - this is an enzyme derived from the fourth stomach chamber of an unweaned ruminant animal (e.g. a calf, kid, or lamb). This enzyme literally breaks apart the proteins in the milk, an action facilitated by the presence of acid (and heat), and separates the milk into curds and whey. The whey is poured off. The curds are then cut, releasing more whey, drained, and molded. At this point, the curds have become cheese.
What is Artisan or Artisanal Cheese?
The word “artisan” or “artisanal” implies that a cheese is produced primarily by hand, in small batches, with particular attention paid to the tradition of the cheesemaker’s art, and thus using as little mechanization as possible in the production of the cheese. Artisan, or artisanal, cheeses may be made from all types of milk and may include various flavorings.
What is Farmstead Cheese?
In order for a cheese to be classified as “farmstead,” as defined by the American Cheese Society, the cheese must be made with milk from the farmer’s own herd, or flock, on the farm where the animals are raised. Milk used in the production of farmstead cheeses may not be obtained from any outside source. Farmstead cheeses may be made from all types of milk and may include various flavorings."
Source: American Cheese Society