Wall cheese
Wall cheese is a term used to refer to a variety of different edible substances that grow on certain walls of Thorgh. The various types of wall cheese vary in consistency; all are more or less solid, but some are soft and spongy, some sticky and pasty, some firm and gelatinous. Their flavors likewise vary, some sweet, some meaty, and some not much like any other common food.
Occurrence
Wall cheese grows naturally on many surfaces throughout Thorgh, the same surface usually generating consistently the same kind of cheese, though there are exceptions—areas that rotate through several different kinds of cheese on a periodic or irregular schedule. Despite the name, wall cheese grows on surfaces of any orientation, and is found as readily on floors and ceilings as on walls. Different types of cheese tend to grow to different thicknesses, although there is some variation even between areas that produce the same type. Some cheeses form films less than a millimeter thick; others grow to form thick mantles of a meter or more. Generally, both extremes of thickness pertain to the softer cheeses; those that form the thinnest films tend to be very soft and pasty in texture; those that form the thickest are firmer, but still soft enough to be easily scraped off or dug through. Harder cheeses usually tend to form in thicknesses of a few centimeters to perhaps a decimeter at most.
While common throughout most of Thorgh, wall cheese only grows in airy environments. No wall cheese forms in Thorgh's inner seas. Whether this is because something about the cheese's formation requires contact with air or simply because Thorgh or its creators arbitrarily decided not to put sources of cheese there is unclear.
Harvesting
Removal of the wall cheese from its source is not difficult. The soft cheeses can be easily scraped or scooped away; harder cheeses may need to be broken up or chipped off. The greatest difficulty with harvesting wall cheese, in fact, isn't to get it off the wall, but to make sure it's still pure. Unsurprisingly for an edible substance, wall cheese tends to attract bugs and worms, and old cheese in particular may grow putrid and wormy. This is truer of the soft cheeses than the hard; some organisms may still burrow into hard wall cheese, but to a lesser degree, and it tends to keep better. With soft cheese, regular harvesting of a particular spot generally keeps down the problems, as the cheese is removed from the wall before it becomes infested. Even in an area not subject to such regular harvesting, however, a hungry person is likely to find enough spots of uncontaminated cheese to eat if he looks hard enough, particularly if he digs down deeply in a thick encrustation.
If harvested from its source, wall cheese grows back relatively quickly, making it one of Thorgh's many convenient renewable resources. Completely depleted wall cheese will regenerate within an average of perhaps two days for the thin films, a week for the thickest accretions, or perhaps twelve to fifteen days for the hardest cheeses. Other thicknesses and hardnesses grow back in intermediate times.
Nutrition
Wall cheese is a very nutritious substance, high in protein and essential fatty acids. Some cheeses also have a high carbohydrate content, though this varies. They also contain considerable magnesium and potassium, as well as vitamins A, B7, D, and K. Other nutrients are also contained in wall cheese which are unnecessary to humans but important to other races. Most of the ellogous races of Thorgh, humans included, find most varieties of wall cheese edible and nutritious, though a few varieties are toxic to some species. The only common race of Thorgh not able to eat most types of wall cheese is the iridian, though even they find a few types edible.
In addition to these nutrients common in nearly all wall cheeses, different wall cheeses may have traces of other important vitamins and minerals as well. Indeed, it's been calculated that a human, or a member of almost any of Thorgh's other races, could live entirely on wall cheese, if he properly balanced his intake of different varieties of cheese to make sure all his dietary needs were accounted for. Few if any inhabitants of Thorgh have actually chosen to follow such a diet, however.
Varieties
Several thousand varieties of wall cheese have been catalogued, though in some cases the distinctions between varieties are superficial subtleties of color, texture, or flavor. Most varieties of wall cheese are confined to specific relatively small areas, though there are some widespread varieties found in scattered locations throughout the world. Among the most famous of these are a red, buttery cheese known as stao; a very filling hard black cheese called oederwalt; a yellow cheese called tammel with a texture and taste somewhat like cookie dough, albeit less sticky; and a peppery, meaty brown cheese called draud with a texture like peanut butter.
Trade
Wall cheese comprises a common trade good on Thorgh. Although it's found throughout the world (except the inner seas), it is more common in some areas than others, and there are many varieties that only occur in small localities that can therefore trade them elsewhere—this describes most varieties, in fact. Some rare types of wall cheese can command very high prices in certain markets. To provide the goods to be sold, some individuals or companies set up harvesting operations on large known cheese fields. The discovery of a new, highly productive cheese source, especially one of a rare or previously unknown cheese variety, can potentially make the finder a very wealthy man.
Some nations even trade wall cheese outside of Thorgh, with other planets with which the living world has commerce. Because even the common varieties are a novelty to these worlds, wall cheese can be sold for a significantly higher price to these foreign worlds than it can to other parts of Thorgh, more than compensating for the increased difficulty of transporting it to Thorgh's surface and getting it to these trading partners.