permitted breeds of cow, pastures, location and method of making, period of maturation, as well as details of their food chemistry. Most global modern production is industrial, with little control of these. This is usually made in rectangular blocks, and by wrapping in plastic no rind is allowed to form. Historical production was all with "raw" milk, although the periods of high heat in making largely controlled unwelcome bacteria, but modern production may use thermized or pasteurized milk. Cheesemaking The cheesemaking process reflects the needs of Alpine transhumant makers. At the high summer slopes timber to "cook" the cheese was abundant, but salt had to be carried up, and was expensive, so little is used compared to many other cheese types. Cantal cheese in the Auvergne region of France, took a different approach, with much less heat, more salt, and more pressing. This became used for Cheddar cheese and other similar English varieties. Alpine cheeses are made to be aged, typically at least for a few months, but often much more. The cows reached the high slopes by about May, and remained until about October. Often they moved in stages as the snow retreated. The highest alpage suitable for grazing is at around . Cheese was made during this period, and mostly stored before bringing down in autumn. Often the same cows and herders made a different kind of cheese from winter milk, and protected varieties may require summer (or winter) milk. The Alpine process introduced three innovations. Firstly "the curd was cut into small particles to facilitate whey expulsion", now done by stirring the cheese with a "cheese harp", a set of metal wires (in French or ). Other types of cheese cut the curd, but not into such small particles. Then the curds were "cooked at high temperatures" and pressed, both reducing the moisture content. The low acidity and salt helps the growth of particular bacteria, especially Propionibacterium freudenreichii subspecies shermanii. It is this that produces the gases, including carbon dioxide, which produce the holes or "eyes" in the cheese. These were generally regarded as a fault if they were large, until 19th-century makers of Emmental began to encourage them, a brilliant stroke from the marketing point of view. On the other hand, Gruyère used to have larger holes than it does now. Traditional Alpine cheeses are made in copper (or at least copper-lined) vats or "kettles", which