A Staff Report from the Straight Dope Science Advisory Board

How they salt peanuts in the shell, and other peanut facts

February 22, 2005

Dear Straight Dope:

How do they salt peanuts while they are still in the shell? This mystery has been plaguing me for years and I just have to know.

Dear Straight Dope:

This question puzzled my friend and me for almost the entirety of a three hour road trip: How are peanuts shelled on a mass production basis like at Planters?

Dear Straight Dope:

Having not found the answer elsewhere to this poser and willing to let you do all the research, we ask: How did peanuts, a South American domesticated crop, make their way to Southeast Asia to become an integral part of that area's cuisine?

Cecil sent all your questions to me, gang--seems I'm now the Straight Dope Science Advisory Board member in charge of dealing with nuts. 

The peanut is a South American groundnut with an ancient history. We can't be certain exactly when it was first used for food, but peanut shells have been found preserved at archeological sites dating as early as 2500 BC. I've seen the claim that "peanuts also have been found in pre-Columbian sites in Zhejiang province in China dating from between 2100 and 1811 BC" (reference 6), suggesting an early introduction to the Old World, but I didn't find enough to corroborate that claim for now. What we can be fairly sure of is that peanuts were used as food in Peruvian settlements as early as 700-800 BC (reference 1), due to the presence of pots with carved peanut shell motifs in burial sites of the Moche people of Peru.

The earliest European exposure to the peanut most likely occurred when the Spanish arrived at Hispaniola in 1502, where the Arawak peoples knew of the food and called it "mani" (reference 2). The first printed Spanish account, from 1535, says, "They sow and harvest it. It is a very common crop . . . about the size of a pine nut in the shell. They consider it a healthy food." It was also encountered by the Portuguese in Brazil, with records dating from the mid-16th century giving it the name "mandubi." Seeing its value as a food, both the Spanish and the Portuguese took it back to Europe with them.

There are four main varieties of peanut (Peruvian, Spanish, Valencia, and Virginia), each of which left South America by a different route. The Spanish variety is a climate-tolerant hybrid that came to Europe by way of Africa after the original transplant failed to thrive. According to reference 3, the variety we most commonly encounter in the United States (the Virginia variety) was taken by the Spanish to West Africa, and then soon traveled back to North America on both trade ships and slave ships. Peanuts of the Peruvian variety traveled to the Philippines on Spanish trade ships, then spread from there to China sometime prior to 1600. It's thought that the peanut spread through the rest of eastern Asia overland from China, not directly as a result of Spanish trade, although it's possible both routes were used. The peanut was probably introduced to the Indian subcontinent from Africa--in fact peanuts were once called the "Mozambique bean" (reference 4). Reputedly, the Portuguese brought the peanut to East Africa, so by extension the Portuguese are responsible for bringing it to parts of south and east Asia.

How are peanuts are salted in the shell? If you were expecting some fancy high-tech process involving nanobots or teleportation, I hope you won't be disappointed to learn that peanuts are salted in the shell simply by soaking them in brine (a mixture of salt and water), then drying them by roasting, leaving a salt residue behind on the nut in the shell. Sometimes a vacuum is used to remove air from the batch before the brine is introduced, but even so the process is fairly basic.

What if you want the peanuts out of the shell? In a typical peanut processing facility, you start by removing foreign material (such as leaves, twigs, dirt, bugs, squirrels, even pieces of metal) with a series of screens, blowers, and magnets. The peanuts are then divided into different batches based on their size by passing them over screens--peanuts that are smaller than the holes fall through, while larger ones are carried to the next set of screens. This sizing is important, because peanuts are shelled by rolling them between large metal drums having a certain gap between them. You want the peanut to be large enough that the shell cracks open when it passes between the drums but not so large that the nut is crushed. Depending on the size and complexity of the operation, several sets of drums with different-sized gaps between them may be used.

Another way to shell peanuts is to use a drum with the peanuts inside it. This type of drum has ridges on its inner surface plus a rotating "beater" that beats against the peanuts, pushing the shells and nuts through holes and out of the drum. In effect, the shells are cracked in the drum, and the act of forcing them through the holes in the drum breaks the cracked shells away. Air jets are used in both types of process to blast the relatively light fragments of shell away from the nuts. Sometimes the nuts are sent on through shakers, other screens, and still more air jets to eliminate any remaining bits of shell.

After this step more screens or even electric eye sorters may be used to pick out undersized or broken pieces. While this is a fairly automated process, some small scale operations use hand-sorting, which seems to me a thankless job that just screams "repetitive stress injury." Me, I think I'll stick to writing Staff Reports.

References

  1. McGee, Harold, On Food and Cooking: The Science and Lore of the Kitchen, 1984.
  2. Sauer, J.D., Historical Geography of Crop Plants--A Select Roster, 1993.
  3. Kaprovickas, A., "The Origin, Variability, and Spread of the Groundnut (Arachis hypogaea)," in The Domestication and Exploitation of Plants and Animals, P.J. Ucko and J.W. Dimbleby, eds., 1969.
  4. "World Geography of the Peanut" website, lanra.anthro.uga.edu/peanut/knowledgebase/ 
  5. US EPA, Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Stationary Point and Area Sources, Section 9.10.2.2., Peanut Processing
  6. Marx, Robert F., and Jenifer G. Marx, In Quest of the Great White Gods, 1992.
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