Some of the Minor Oil Crops

Ernest B. Kester.

In ordinary times we could get along very well with an adequate supply of the oils and fats from soybeans, peanuts, cottonseed, corn, and milk, which we produce or import in huge amounts. But in times of emergency, when outside supplies are cut off, we must supplement our domestic production with every available pound from every available source. That, plus the fact that some oils have properties that adapt them to specific uses, is why we are interested in minor oil crops.

Furthermore, many of the minor crops can be exploited as small-business ventures and may yield a fair return to a few investors who care to go into the vegetable-oil industry with a moderate outlay for equipment.

The minor vegetable oils fall into four general classes:

1. Oils from oil-bearing agricultural wastes, such as fruit pits, tomato pomace, wine pomace, and olive mare, and the seeds of citrus fruits, apples, pears, pumpkin, squash, and pimento.

2. Oils from seeds and grains that mostly are raised as crops, including rice, safflower, sunflower, okra, castor, mustard, rape, and tobacco.

3. Oils of tree nuts almond, walnut, pecan, and filbert.

4. Fruit-flesh oils olive and avocado.

A few of the oils listed are second in importance only to our major bulk oils, but that is true only because of sizable importations. As recoverable oils from domestic crops, they are still in the class of minor oils.

It must be borne in mind that the existence of a potential supply of any given oil does not mean that a profit can be realized by recovering it, even at high market prices. Numerous economic factors have to be considered.

By oils and fats, we usually mean the nonvolatile oils that occur naturally as chemical combinations of glycerin and fatty acids. We shall not consider here the volatile or essential oils that are valued for their fragrance or flavor, such as peppermint, wintergreen, and citronella. Also excluded are certain vegetable waxes, which in many respects resemble oils and fats but do not have the glyceride structure.

Vegetable oils differ from one another mainly in the kind and amount of combined fatty acids, and the classes, kinds, and amounts of impurities present. Therefore, the properties of the various vegetable oils usually differ only in degree, except in a highly individual oil that contains a large percentage of some unique constituent. For example, castor oil contains a high percentage of combined ricinoleic acid, and tung oil a large amount of eleostearic acid, neither of which is ordinarily found in vegetable oils to any great degree.

Oils are characterized also by their iodine value. That term the oil technologists use to describe the drying power, or lack of it, in an oil. High-iodine oils (linseed, walnut, tung) are usable in paints and other surface coatings. Those with low iodine values (cottonseed, rice-bran, olive) do not form hard films when they are exposed to air.

THE PIT OILS of the apricot, peach, prune, and plum strikingly resemble one another in composition and, indeed, are not readily differentiated. Cherry-pit oil has a somewhat higher iodine value. These oils are like sweet-almond oil, for which they are sometimes substituted. If the pits are processed promptly after removal from the fruit, little or no "oil of bitter almonds" will be liberated into the fixed oil by chemical reaction. The pit oils command a premium price over the commoner vegetable oils and are usually handled by brokers in essential oils.

Our annual crop of apricots averages more than 240,000 tons, of which more than 80 percent is dried, canned, or otherwise processed. Many growers dry their fruit and sell the pits at attractive prices. Several plants in California shell apricot pits to recover kernels, for which there is a strong domestic market, particularly for making macaroon paste. The dry-pit equivalent for apricots processed each year in the United States is about 12,000 tons, which would yield about 3,000 tons of kernels. In the cracking process, many kernels are broken; they are used to recover oil. Our production of apricot-pit oil is about 100 tons a year. It is used largely for making cosmetics and pharmaceuticals.

Most of the peach crop in the East and Midwest is marketed as fresh fruit. Because California produces about 90 percent of the peaches processed in the entire country, only there could you consider peach pits as a source of oil and other byproducts. The pits from the peaches processed in California could yield about 1,400 tons of oil a year. At present, peach pits can be obtained from canneries and drying yards for little or nothing except cost of haulage. A comparatively small proportion of the available pits is converted into char for poultry feeds and fuel briquets. Very little peach-kernel oil is extracted, because most of the pits available for byproducts are from canners' clingstone peaches, which when wet yield less than 1 percent of oil, and because many modern canneries use a saw that cuts the entire peach, including pit, in two, crushing the kernel into fragments that are hard to recover. Where freestone pits are available, oil recovery is more practical. The kernels, from the whole pits obtained from drying yards, can be separated in the equipment used for apricot pits. Eleven tons of dry freestone pits yield about a ton of kernels, from which about 0.4 ton of oil can be pressed. Screw presses can be used, but the one plant that operated on peach pits in California employed hydraulic presses used in hot-pressing olive oil.

Processed cherries, both sweet and sour, are marketed pit-free as canned, frozen, and brined products. The oil represented by the total of pitted cherries amounts to about 1,100 tons a year, but no plant at present is recovering it. One company in Wisconsin produced a few tons of cherry-kernel oil a few years ago, and another used cherry pits as a source of the "oil of bitter almonds." The operations for recovering cherry-kernel oil are similar to those used for peach- and apricot-pit oils.

No fruit pits other than peach, apricot, and cherry are likely sources of oil. Only small amounts of prune pits are available for processing because most of the prune crop is marketed without removal of the pits. Volumes of plum and date pits from processing plants are comparatively small. In pressing olives for oil, the whole fruit, including pit, is crushed. In plants where pitted olives are canned, the pits are a waste product, but the oil content of 3.5 to 7 percent is probably too low for profitable recovery. Inclusion in animal feeds has been suggested, but such a material, unless well ground, would undoubtedly contain hard, sharp particles, which might injure the digestive tract.

The oil of citrus seeds resembles cottonseed oil in general properties. The approximate amounts obtainable from food-processing operations are: Grapefruit-seed oil, 2,600 tons; Valencia orange-seed oil, 1,200 tons; and lemon-seed oil, 500 tons.

Florida, Texas, Arizona, and California produce grapefruit in commercial quantities, but only Florida processes seeded varieties in tonnages large enough that the seeds might be considered a practical source of vegetable oil. One plant in Florida manufactures the oil in considerable amounts.

California, Arizona, and Florida produce Valencia oranges, the only major seed-bearing variety grown in this country. The seed content varies greatly. Orange seeds contain about 40 percent of oil, which can be readily expressed or extracted. The oil is easily refined to a pleasing, light-colored, bland product, useful for foods and other purposes.

Lemons, unlike oranges, are not a seasonal crop. Fruit in all stages of ripeness can be found on a tree. It is an interesting fact that a cold snap or freeze will be followed, after an interval of months, by a crop of lemons that have an unusually high seed content. The processing of lemons commercially is confined to southern California.

More than 90 percent of our grapes are grown in California; where the 500,000 acres in vineyards are more than double the acreage devoted to oranges. Here we find principally the Vinifera or Old World type of grape. The Great Lakes region is a center for the production of the Lubrusca or slipskin type, of which the Concord is representative.

Grape seeds are available in the wastes from the raisin and the wine industries, particularly the latter. In former years, raisins were made almost exclusively from seed-bearing grapes (principally of the Muscat variety) ; large quantities of seeds, rejected from drying plants, were used in making oil, brandy, tartrates, and stock feed. As the Thompson seedless grape has developed, the tonnage of Muscats converted to raisins has dwindled, and in 1948 less than 10,000 tons of that variety was dried. In terms of vegetable oil, it equals about 45 tons. One plant is producing raisin-seed oil by expression methods. This oil is used in oiling packaged raisins to make them free flowing.

The flourishing wine industry in California has made available large quantities of the grape pomace, from which seed can be readily separated by either dry or wet methods. At least three mills in California are now producing grape-seed oil by extraction from the seeds of wine pomace. On the basis of an annual crush of a million tons of grapes, the quantities of recoverable oil would be about 3,200 tons if all the pomace were processed. Only a fraction of the wine pomace is worked for oil and byproducts.

Grape-seed oil is excellent for culinary purposes. As it is semidrying, it can be used together with other oils in paint formulations.

SEVENTY PERCENT of domestic apples used in processing are raised in the Western States and North Atlantic States. The seed from the part of the annual apple harvest that is canned, dried, and frozen would yield about 385 tons of oil. Economical recovery, however, would be limited to the larger districts, in which case the maximum amount of oil would be reduced to 270 tons. Only large packing centers would be justified in separating seed from waste and would in most instances dispose of the seed to oil mills.

California and Washington, centers of production of pears for canning and drying, account for 90 percent of the national total. The output of processed pears in California is roughly double that of Washington. Not more than about 150 tons of oil could be realized from pear seeds as a total for both areas. Apple- and pear-seed oils are quite similar. Both can be refined to a pale, bland product entirely suitable for culinary purposes.

The principal cranberry-producing States are Massachusetts, New Jersey, and Wisconsin. Washington and Oregon account for 3 to 4 percent of the national total. About a third of the cranberries raised are made into seed-free manufactured products, principally sauce. The oil yield possible from the seed rejected in processing would not exceed 5() tons. More valuable than the seed oil is the ursolic acid in the skins. This chemical, in the form of its sodium salt, is a powerful agent for production of water-in-oil emulsions. Neither cranberry-seed oil or ursolic acid is now in commercial production.