Sago is a starch extracted from the pith inside stems of the sago palm Metroxylon sagu. Sago forms a major staple food for the lowland peoples of New Guinea and the Moluccas where it is called sagu and traditionally is cooked and eaten in the form of a pancake served with fish.
Sago looks like many other starches, and both sago and tapioca are produced commercially in the form of "pearls". These two kinds of pearls are similar in appearance and may be used interchangeably in some dishes. This similarity causes some confusion in the names of dishes made with the pearls.
Because sago flour made from Metroxylon is the most widely used form, this article discusses sago from Metroxylon unless otherwise specified.
Sago palms grow very quickly, up to 1.5m of vertical stem growth per year, in the fresh water swamps and lowlands in the tropics. The stems are thick and either self supporting or grow with a somewhat climbing habit. The leaves are pinnate, not palmate. The palms are harvested at the age of 7 to 15 years just before they flower. They only flower and fruit once before they die. When harvested the stems are full of the stored starch which would otherwise be used for flowering and fruiting. The trunks are cut into sections and into halves and the starch is beaten or otherwise extracted from the "heartwood", and in some traditional methods it is collected when it settles out of water. One palm yields 150 to 300kg of starch.
In addition to its use as a food source, the leaves and spathe of the sago palm are used for construction materials, for thatching roofs, and the fibre can be made into rope.
Sago (Metroxylon) is made through the following steps:
Sago flour (Metroxylon) is nearly pure carbohydrate and has very little protein, vitamins, or minerals. However, as sago palms are typically found in areas unsuited for other forms of agriculture, sago cultivation is often the most ecologically appropriate form of land-use, and the nutritional deficiencies of the food can often be compensated for with other readily available foods.
One hundred grams of dry sago yields 355 calories, including an average of 94 grams of carbohydrate, 0.2 grams of protein, 0.5 grams of dietary fiber, 10mg of calcium, 1.2mg of iron, and negligible amounts of fat, carotene, thiamine, and ascorbic acid.
Sago can be stored for weeks or months, although it is generally eaten soon after it is processed.
The sago starch is then either baked (resulting in a product analogous to bread or a pancake) or mixed with boiling water to form a kind of paste. Sago can be made into steamed puddings such as sago plum pudding, ground into a powder and used as a thickener for other dishes, or used as a dense glutinous flour.
The starch is also used to treat fibre to make it easier to machine. This process is called sizing and helps to bind the fibre, give it a predictable slip for running on metal, standardise the level of hydration of the fibre, and give the textile more body. Most cloth and clothing has been sized and this leaves a residue which is removed in the first wash.
Pearl sago, a commercial product, closely resembles pearl tapioca. Both typically are small (about 2 mm diameter) dry, opaque balls. Both may be white (if very pure) or colored naturally grey, brown or black, or artificially pink, yellow, green, etc. When soaked and cooked, both become much larger, translucent, soft and spongy. Both are widely used in South Asian cuisine, in a variety of dishes, and around the world, usually in puddings. In India, pearl sago is called sabudana ("whole grain") and is used in a variety of dishes.
Growing up to 30 meters in height, the sago palm, Metroxylon sagu, is found in tropical lowland forest and freshwater swamps, and can grow in a wide variety of soils. The palm genus Metroxylon has several species. The main source of sago flour is Metroxylon sagu, which is found in Southeast Asia and New Guinea; other species, including M. salomonense and M. amicarum are found in islands in Melanesia and Micronesia where it less important economically as a source of consumed sago.
Processed starch known as sago is made from this and other cycad plants, and is a less frequent food source for some peoples of the Pacific and Indian Oceans. There is a large difference both biologically and dietarily between the two types of sago. Sago as a major dietary food source comes mainly from a palm in the genus Metroxylon. Despite their common name, cycads are not palms (i.e. they are not members of the family Arecaceae but rather from Cycadaceae, a vastly different taxonomic order: cycads, sometimes called living fossils, are gymnosperms while palms are angiosperms).
Sago from the cycad is very different, because unlike Metroxylon, cycad seeds contain highly poisonous compounds. Consumption of cycad seeds has been implicated in the outbreak of Parkinson's Disease-like neurological disorder in various locations in the Pacific such as Guam. Highly toxic cycasin and BMAA compounds are found in most parts of the plant. These must be removed through extended processing before any part can be safely eaten. First, the pith made from the trunk, root, seeds is first ground to a coarse flour, washed carefully to leach out natural toxins, then dried and cooked to become a starch similar to tapioca and is used for many of the same purposes.