Processing

Peanuts may be processed shelled or unshelled, depending on the desired end product. Those left unshelled are mainly of the Virginia and the Valencia types. They are separated according to pod size by screening; discolored or defective seeds are removed by electronic color sorting, and the stems and immature pods are removed by specific gravity (Cole and Dorner 1992). Peanuts that are to be salted and roasted in the shell are soaked in a brine solution under pressure, and then dried and roasted.

Peanuts to be shelled are passed between a series of rollers, after which the broken shells and any foreign materials are removed by screens and blowers. Next, the shelled peanuts are sorted by size. Any remaining foreign materials and defective or moldy seeds are removed by an electronic eye, which inspects individual seeds. Ultraviolet light is useful for detecting aflatoxin contamination.

Peanuts are frequently blanched to remove the skins and hearts. This can be done by roasting (259-293° F for 5 to 20 minutes), or by boiling, after which they are rubbed to remove the skins. Then the kernels are dried to 7 percent moisture and stored, or converted into various peanut products.

Another method - dry roasting - is popular because it develops a desirable color, texture, and flavor for peanut butter, candies, and bakery products. In this case, unblanched peanuts are heated to 399° F for 20 to 30 minutes, then cooled and blanched.

Shelled peanuts are usually dry roasted in a gas-fired rotary roaster at 399° F, then cooled to 86° F, after which they are cleaned and the skins removed for making peanut butter. Oil-roasted peanuts are placed in coconut oil or partially hydrogenated vegetable oil at 300° F for 15 to 18 minutes until the desired color is achieved, whereupon a fine salt is added. Roasting makes the tissue more crisp by drying and also enhances flavor because of the browning reaction. Relatively low temperatures are used to avoid scorching the outside before the inside is cooked through. The roasting of peanuts also reduces aflatoxin content. For example, roasting for a half hour at 302° F may reduce aflatoxin Bj content by as much as 80 percent (Scott 1969).

And finally, peanut oil is extracted by one of three different methods: hydraulic pressing, expeller pressing, or solvent extraction.