Pine nuts are the edible seeds of pines (family Pinaceae, genus Pinus). About 20 species of pine produce seeds large enough to be worth harvesting; in other pines the seeds are also edible, but are too small to be of value as a human food. Pine nuts contain (depending on species) between 10â€“34% protein, with Stone Pine having the highest content. They are also a source of dietary fiber. When first extracted from the pine cone, they are covered with a hard shell (seed coat), thin in some species, thick in others. The nutrition is stored in the large female gametophytic tissue that supports the developing embryo (sporophyte) in the centre. Although a nut in the culinary sense, in the botanical sense pine nuts are seeds; being a gymnosperm, they lack a carpel (fruit) outside. The shell must be removed before the pine nut can be eaten. Unshelled pine nuts have a long shelf life if kept dry and refrigerated (at â€“5 to +2 Â°C); shelled nuts (and unshelled nuts in warm conditions) deteriorate rapidly, becoming rancid within a few weeks or even days in warm humid conditions. Pine nuts are commercially available in shelled form, but due to poor storage, can have poor flavour and may be already rancid at the time of purchase.