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close this bookAmaranth to Zai Holes, Ideas for Growing Food under Difficult Conditions (ECHO; 1996; 397 pages)
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View the documentAbout this book
View the documentAcknowledgements
Open this folder and view contents1: Basics of agricultural development
Open this folder and view contents2: Vegetables and small fruits in the tropics
Open this folder and view contents3: Staple crops
Open this folder and view contents4: Multipurpose trees
Open this folder and view contents5: Farming systems and gardening techniques
Open this folder and view contents6: Soil health and plant nutrition
Open this folder and view contents7: Water resources
Open this folder and view contents8: Plant protection and pest control
Open this folder and view contents9: Domestic animals
Open this folder and view contents10: Food science
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Open this folder and view contents12: Seeds and germplasm
Open this folder and view contents13: Energy and technologies
Open this folder and view contents14: From farm to market
Open this folder and view contents15: Training and missionary resources
Open this folder and view contents16: Oils
Open this folder and view contents17: Above-ground (urban) gardens
View the document18: What is ECHO?
View the documentAdditional ECHO publications
Open this folder and view contentsECHO development notes - issue 52
Open this folder and view contentsECHO development notes: issue 53
close this folder28 additional technical notes about tropical agriculture
View the documentA few alternate seed sources that we commonly use
View the documentAmaranth - grain and vegetable
Open this folder and view contentsArid region farming primer
View the documentCitrus propagation and rootstocks
Open this folder and view contentsCucurbit seeds
Open this folder and view contentsDry farming
View the documentMuscovy ducks for png villages
View the documentFruit crops
View the documentFruit vegetables
View the documentGrain crops
View the documentGround covers and green manures
View the documentGreen manure crops
View the documentIndustrial crops
View the documentThe lablab bean as green manure
View the documentLeafy vegetables
View the documentLeguminous vegetables
View the documentThe moringa tree
View the documentRecipes to learn to eat moringa
View the documentMiscellaneous vegetables
View the documentThe poor man's plow
View the documentPulses (grain legumes)
View the documentRabbit raising in the tropics
View the documentLetter from fremont regier, mennonite central committee, Botswana (and earlier in Zaire)
View the documentRoots and tubers
View the documentSunnhemp as a green manure
View the documentThe sweet potato
View the documentTropical pasture and feed crops
View the documentThe velvet bean as green manure
Open this folder and view contentsPrinciples of agroforestry
Open this folder and view contentsGood nutrition on the small farm
 

The sweet potato

by Franklin W. Martin

Why grow sweet potatoes?

Sweet potatoes are already the 6th or 7th most produced food crop in the world, surpassed only by wheat, rice, corn, potato, barley, and possibly cassava. Among the reasons that sweet potato is a great crop is that it is relatively easy to grow, relatively free of pests and diseases, has relatively high productivity, and is always good food, principally starch, some protein and vitamin C, and, in orange varieties, rich in vitamin A. In addition, the young leaves, rich in protein and most vitamins, are also good food. Furthermore, the sweet potato is an excellent animal food. Its ability to produce in poor soils makes the sweet potato an especially good crop for poor tropical soils where fertilizer is not available. If the leaves are also used as food, sweet potato will probably produce more nutrients per acre than almost any other crop under those conditions. (The other tropical crop which produces well on poor soils and also has both edible roots and leaves is cassava. It has an advantage over sweet potato in drought tolerance, but sweet potato has the advantage in nutrients. That is because substances called polyphenols in the cassava leaf combine with protein during cooking and reduce the amount of protein that is digestible.) Nevertheless, like all crops the sweet potato must be produced with understanding in order to obtain maximum yields. It should never be treated with neglect.

Principle uses of sweet potatoes, and techniques

Leaves. The sweet potato plant can be harvested for leaves during the 2nd and 3rd months of production. Only the tender stem and young, not fully developed leaves, which constitute the distal 2-4 inches of the growing stem, should be taken. The leaves and stems are boiled for 15-20 minutes, washed, seasoned, and served.

Boiled sweet potato. The sweet potato is washed, peeled and trimmed, cut into 1 inch thick slices or cubes, and boiled 18-20 minutes. The boiling water is then discarded. The sweet potato can then be served as is, mashed, or combined in many dishes (casseroles). The mashed pulp can be used as a partial substitute for wheat flour in baked products such as pancakes, cakes, flat breads, cookies, fritters, or even bread.

Baked sweet potato. The entire sweet potato is wrapped and then baked in a modern or primitive oven until soft (one hour at 350 degrees C). During baking of most sweet potatoes, part of the starch is converted to the reducing sugar, maltose, thus increasing sweetness.

Osmotically modified boiled sweet potato. The peeled and trimmed sweet potatoes can be cut into thin (1/8") slices, placed in water 2 hours (moved once in a while) and then boiled. The products will be clearer, less sweet, and milder than those made from untreated sweet potatoes. (What is happening chemically is that the enzymes and substrates responsible for polyphenolic oxidation are partially lost, as well as some of the sugars).

Sweet potato flour. The flour of sweet potato is much more difficult to make than that of potato because the reducing sugars readily released from the starch combine with free amino acids to produce disagreeable colors, odors, and flavors. To avoid this the peeled sweet potato can be shredded, and the shreds immersed in water 2 hours. This process works better if the water is changed 2-3 times. The shreds are drained and then dried, first in the shade (with air movement or wind) and later in the sun (in some cases, drying over the stove or in an oven will be necessary). The brittle shreds are easily crushed to flour, or this can be done rapidly in a household blender. The flour can be stored for 6 months or more in sealed containers. It can be used as a substitute for wheat flour in the following amounts: 100% in white sauces, 25-50% in cookies, cakes and flat breads, and 15-20% in breads. From the water, starch can be recovered (see below).

Starch production. The peeled sweet potato is ground in a mill or blender as finely as possible, and mixed with 5-10 times its weight in water. The starch settles out, and the water is carefully poured away (can be used as pig feed). The starch is then mixed with water 1-3 times more and the process is repeated. After the last settling the water is carefully drained and the starch is dried on a metal surface in the sun. It can be used as is any starch, such as corn or potato starch, and can be stored in sealed containers for a year or more.

Breakfast cereal. A breakfast food similar to "cereal" can be made from any sweet potato. The sweet potato is grated (not as finely ground as for starch), suspended in water, and filtered through a cloth. The liquid is saved for starch, the residue is suspended 1-3 times more in water, and filtering is repeated. The portion of the sweet potato that does not

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