It will not normally be present in any specification or declared substances due to accident or negligence rather than intent, and also for the introduction of unwanted substances after the product has been made. Adulteration therefore implies that the adulterant was introduced deliberately in the initial manufacturing process, or sometimes that it was present in the raw materials and should have been removed, but was not.
An adulterant is distinct from, for example, permitted food preservatives. There can be a fine line between adulterant and additive; chicory may be added to coffee to reduce the cost or achieve a desired flavor—this is adulteration if not declared, but may be stated on the label. Chalk was often added to bread flour; this reduces the cost and increases whiteness, but the calcium actually confers health benefits, and in modern bread a little chalk may be included as an additive for this reason.
In wartime adulterants have been added to make foodstuffs "go further" and prevent shortages. The German word ersatz is widely recognised from such practices during World War II. Such adulteration was sometimes deliberately hidden from the population to prevent loss of morale and propaganda reasons. Some goods considered luxurious in the Soviet Bloc such as coffee were adulterated to make them affordable to the general population.
Past and present examples of adulterated food, some dangerous, include:
Historically, the use of adulterants has been common; sometimes dangerous substances have been used. In the United Kingdom up to the Victorian era, adulterants were common; for example, cheeses were sometimes colored with lead. Similar adulteration issues were seen in industry in the United States, during the 19th century. There is dispute over whether these practices declined primarily due to government regulation or to increased public awareness and concern over the practices.
In the early 21st century, cases of dangerous adulteration occurred in the People's Republic of China.
In some African countries, it is not uncommon for thieves to break electric transformers to steal transformer oil, which is then sold to the operators of roadside food stalls to be used for deep frying. When used for frying, it is reported that transformer oil lasts much longer than regular cooking oil. The downside of this misuse of the transformer oil is the threat to the health of the consumers, due to the presence of PCBs.
Adulterant use was first investigated in 1820 by the German chemist Frederick Accum, who identified many toxic metal colorings in food and drink. His work antagonized food suppliers, and he was ultimately discredited by a scandal over his alleged mutilation of books of the Royal Institution library. The physician Arthur Hill Hassall conducted extensive studies in the early 1850s, which were published in The Lancet and led to the 1860 Food Adulteration Act and other legislation. John Postgate led a further campaign, leading to another Act of 1875, which forms the basis of the modern legislation and a system of public analysts who test for adulteration.
At the turn of the 20th century, industrialization in the United States led to a rise in adulteration which inspired some protest. Accounts of adulteration led the New York Evening Post to parody:
Mary had a little lamb,
And when she saw it sicken,
She shipped it off to Packingtown,
And now it's labeled chicken.
However, even in the 18th century, people complained about adulteration in food:
"The bread I eat in London is a deleterious paste, mixed up with chalk, alum and bone ashes, insipid to the taste and destructive to the constitution. The good people are not ignorant of this adulteration; but they prefer it to wholesome bread, because it is whiter than the meal of corn [wheat]. Thus they sacrifice their taste and their health. . . to a most absurd gratification of a misjudged eye; and the miller or the baker is obliged to poison them and their families, in order to live by his profession." – Tobias Smollett, The Expedition of Humphry Clinker (1771)