Processed cheese is produced by first melting cheese and adding so called melting salts. Because of these melting salts the cheese will remain spreadable after cooling down. Depending on the substance added processed cheese can be made into blocks that can be cut or sliced or into melted cheese to be used on bread. By adding other ingredients the processed cheese can in fact be made usable for any means. For instance processed cheese for pizza's (the processed cheese has to melt fluenty, get a nice brownish color and make threads when cut). Processed cheese for cheeseburgers for instance may not drip, not make threads and may not burn mouth or lips when being eaten.
Processed cheese has many advantages. Processed cheese is for instance used in many frozen foods like pizza's, gordon bleu's etc because of the melting capacity of processed cheese and the nice layer of cheese that develops. Another advantage is food safety. By heating the cheese to at least 95 degrees Celsius processed cheese had very good microbiological qualities. A third important advantage of processed cheese is that it can be kept longer dan regular cheese. Especially in earlier times this was an important thing to consider.
With the introduction of refridgerators this advantage decreased for develloped countries but for instance in the less developed and more southern countries this advantage still is very important. The main advantage of processed cheese is however that it can be adjusted to the needs of the client maintaining the quality and taste of the product.
Just to make things clear, not all spreadable cheeses are processed cheese. Cheeses like Munster or Brie are for instance soft, almost spreadable cheeses but not processed cheeses. The same goes for Mascarpone and soft goatcheese. Cream cheese is also often called a speadable cheese because of the productproperties but in fact it is not a processed cheese at all.