Peanut roasting

Dry roasting uses an oven temperature of around 430°C, and the temperature of the peanuts raised to around 160°C for 40 to 60 minutes.

However the actual temperature varies between the peanut's condition and the desired end characteristics. In some of the roasting conveyer oven, there are the uses of hot countercurrent hot air, whereby the air roast the peanut kernels individually giving an even roast.

The roasted peanut are then cooled and blanched. In the cooling process, it occurs in the cooling boxes or on the conveyer belt whereby air was used to blow over the peanuts immediately after the roasting it. This process is very important as so to stop the roasting process thus giving a uniform quality. The blanching method such dry, water, spin, air impact was used to remove the peanut's skin and also moulds, dust and other foreign material.

Dry blanching is more commonly used in peanut butter production.
This is because it removes the kernel hearts which would affect the peanut butter flavour.
In dry blanching, the peabuts are heated to around 138°C for 25 minutes, so to crack and loosen the skins. The heated peanuts are then cooled and passed through the brushes or ribbed rubber belting to rub off the skins. The hearts of the peanuts would be separated from the cotyledons (peanut halves) by screening.

Water blanching passes the peanuts on conveyors through stationary blades that slit the peanut
skins. Hot water sprayers would then be used to loosen the peanuts' skins and the oscillating canvas-covered pads on the knobbed conveyor belts would removed the skins as the peanuts passed through. Water blanching also requires the drying of the peanuts back to a moisture content of aound 6 to 12 percent.

Spin blanching uses steam to loosen the skins of the peanuts. Steaming is followed by
spinning the peanuts on revolving spindles as the peanuts move, single file, down a grooved conveyor. The spinning process would unwraps the peanut skins.

Air impact blanching uses a horizontal drum (cylinder) in which the peanuts are placed and
rotated. The inner surface of the drum has an abrasive surface that aids in the removal of the skins as the drum rotates. Inside the drum are air jets that blow the peanuts counter to the rotation of the drum creating air impact which loosens the skin. The combination of air impacts and the abrasive surface of the drum results in skin removal. Either batch or continuous air impact blanching can be conducted.

Taken from:
Jasper Guy Woodroof, Peanuts: Production, Processing, Products, 3rd Edition, Avi
Publishing Company, Westport, CT, 1983.
Peanut processing. Retrieved April 23, 2008 from epa.gov Website: http://www.epa.gov/ttn/chief/ap42/ch09/final/c9s10-2b.pdf