It seems it was common practice for flour sellers to mix horrible things (even poisons) in their product to bulk it up and make it whiter. Apparently tea was also subject to this type of fraud.
“Adulteration of Flour – At the Mansion-house on Saturday, a flour-factor appeared to a summons charging him with selling five sacks of adulterated flour, contrary to the provision of the Act 4th Geo. IV., commonly called the Bakers’ Act. The complainant, a baker residing in the Hackney-road, stated that on the 7th inst. he purchased the flour in question from the defendant. On tasting it he felt convinced that there was a quantity of plaster of Paris, beans, &c. mixed with it, and he therefore sent a sample of it to Mr. Clarke, of Apothecaries’-hall, to be analysed. – Mr. Clarke stated that he had been in the habit of analysing flour and other articles of food for Government for the last 25 years, and that he had analysed the sample of flour produced; the result of the experiment convinced him there was no plaster of Paris in it; but he found that on fifteenth part of in consisted of beans, and the remainder was flour of the coarsest dewscription. – The Lord Mayor asked Mr. Clarke if there was any thing in the flour unwholesome, or likely to prove injurious to the consumer, to which her replied in the negative. His Lordship said, that being the case, he could not convict under the Act, and the complainant must seek his remedy by and action at law, and he should therefore dismiss the complaint. – His Lordship then asked Mr. Clarke whether the flour was ever adulterated with plaster of Paris, to which Mr. Clarke replied, that a short time since he went down to Hull, by order of the Lords of the Treasury, to analyse samples of 1467 sacks of flour, then at the Custom-house there, to be shipped for Spain and Portugal; and on examination, found one-third of it was plaster of Paris, one-third burnt bones and beans, and the reminder of the flour of the coarsest description. Mr. Clarke also said that he was at present engaged by order of Government in analysing several chests of Caper Souchong Tea, and although he had only examined a few of them, yet he found that one-fourth of their contents was lead ore, or poison of the rankest description, and he knew from experience that a great quantity of tea was adulterated in a similar manner.”
The Stamford Mercury, 29th July, 1825.