Horrifying, but not always for the reasons that you might think.
When you think about food safety in the early 20th century, the first thing that comes to mind is probably Upton Sinclair's The Jungle, the big expose of the meatpacking industry in Chicago. It was intended to be a pro-labor text, not a health-minded one, but it made a big impact as Americans became disgusted with the idea that they were consuming moldy, slimy sausage that had been returned to the factory to be mixed with fresh sausage (to name one example). Coming as it did right as the Pure Food and Drug Act was being debated, The Jungle was a big deal. But it wasn't the only deal.
By the end of the 19th century, food in the United States had become an industrialized, mass-produced commodity. At the start of the century, most people in the United States lived rural lives and ate locally. The state of transportation technology meant that it took a long time to ship cargo from place to place. Only the most hardy or simple food would last long enough when canals and sailing ships were the height of technology.
Steam transport changed that. With steamships and railroads, transportation sped up. It became possible to bring food from the railroad-spiked West to the cities of the East. The great cattle drives of Texas and the plains wouldn't have happened without the railroads to haul those animals east, the slaughterhouses of Chicago to turn them into edible steaks and sausage, or the buyers in New York, Philadelphia, Baltimore, and Boston.
Even with improved transportation, food companies still had problems. Refrigeration didn't start to become significant until after World War I, and so food preservation was a significant issue. Canning worked, but canning was expensive, and so companies began to experiment with alternatives.
Chemical alternatives.
During the Spanish-American War, the United States found itself not just needing to recruit and train fighting men — it also needed to feed and equip them. From this need came one of the great scandals of the first decade of the 20th century, the Embalmed Beef Scandal.
In Cuba and Puerto Rico, soldiers were fed canned and refrigerated beef that made many of them sick. Gen. Nelson A. Miles, commander of the U.S. Army, said the meat had an "odor like an embalmed dead body."
Nelson laid some series charges against the head of the Army's commissary corps and the companies that supplied it. The commissary general called Miles a liar and said he wished Miles would be "covered with the contents of a camp latrine." The investigations that followed Miles' accusations lasted longer than the Spanish-American War itself but ultimately found that the problems with the beef were due to mishandling in the field.
This wasn't the end of the story, however. Civilians were finding problems with their meat as well, and as was the case with the Army, it was thought that the preservatives were to blame. In 1902, Dr. Harvey Washington Wiley — chief chemist of the U.S. Agriculture Department — held the first meeting of what would eventually become known as The Poison Squad.
His goal was to test how much of (and if) the day's common preservatives — borax, various acids, etc. — were needed to make a person ill. He was deliberate in his work and meticulous in his measurements. Naturally, the newspapers ate up his story and his work. He became a national figure, famous and controversial.