Now only the peanut kernels are left. They're poured into a grinder. Smooth peanut butter is what kids like best. Crunchy is what adults prefer. Usually salt is added, and sometimes sugar and vegetable oil. Then the peanut butter is packed into jars and sent to stores.
If it's "natural" peanut butter, you'll need to stir it up after you open the jar. That's because the peanut oil will float to the top. Hydrogenated peanut butter doesn't separate. Invented in the 1920s, it's the top-selling kind today.
Humans have been eating peanuts for thousands of years. Jars of peanuts have been discovered in Incan tombs dating to 1500 BC. But humans in North America were not as quick to catch on. By 1800, huge peanut crops were being grown in South Carolina as animal feed. Peanuts were pig food until the Civil War.
Food became scarce, and soldiers on both sides of the conflict turned to peanuts (known then as "goobers") as an alternative to meat. In 1890, a St. Louis physician, looking for an easily digestible form of protein for his patients without teeth, poured some peanuts into his meat grinder. He turned the crank and out came history's first batch of peanut butter. The unknown doctor never patented his invention. Cereal giant John Harvey Kellogg did, though, in 1895.
Around 1900, peanuts (and peanut butter) began to get popular. First, inventor George Washington Carver began promoting peanuts as a valuable crop. Second, new machinery was marketed that could harvest and clean peanuts faster and better than humans could.
The 1904 World's Fair in St. Louis showcased peanut butter as an ideal, nutritious food. It was a hit. But it took a war to spread peanut butter's appeal.
During World War II, meat and butter were scarce and expensive. Peanut butter was available, cheap, and nutritious. Soldiers in the war and people at home began to eat it more. After the war, the demand for peanut butter increased.